Bird Biogeography

• the Palaeognathae, which includes the ratites & tinamous, and
• the Neognathae, which includes all other living birds.

Currently, taxonomists recognize 40 orders, 233 families, 2229 genera, and over 10,000 species of birds. Birds occupy all continents and habitats but, of course, some continents & some habitats have more species than others.

How are birds currently distributed throughout the planet and what factors have contributed to this distribution? In part, the current distribution of birds has been influenced by historical events. Birds belonging to various lineages have been found in Cretaceous deposits of Asia, Europe, and North and South America. Prominent and well-known Cretaceous bird taxa included the Enantiornithes, a fairly diverse group of birds, mostly flying forms; Hesperornithiformes, toothed birds (see drawing below) which were mostly flightless swimmers; and Ichthyornithiformes, toothed flying birds that probably fed on fish. These taxa are extinct today, but by the close of the Cretaceous, representatives of several modern bird taxa were sharing the skies with these extinct birds. A birdwatcher 65 million years ago could have seen relatives of today's loons, geese and ducks, albatrosses and petrels, and gulls and shorebirds, and possibly other familiar birds as well.

What does the fossil record reveal concerning the present-day distribution of birds? The study of historical bird geography is difficult because of the many variables involved: evolution, climatic change, shifting vegetation, weather disasters, epizootics, rapid dispersal, ecological adaptation, competition between species, and barriers (Welty & Baptista 1988). However, it is known that (Proctor and Lynch 1993):

• all modern orders of birds likely arose from a common (but as yet uncertain) ancestral stock during the Cretaceous (more than 65 million years ago).
• the Paleocene & Eocene (37 - 65 million years ago) may have been a time of great radiation ("Tertiary explosion"; Feduccia 1995, 2003), with as many as 16 new orders developing (but, see "Fossil Evidence for the Extant Avian Radiation in the Cretaceous" below) .

Fossil Evidence for the Extant Avian Radiation in the Cretaceous -- Clarke et al. (2005) provide apparent evidence that cousins of living birds coexisted with dinosaurs more than 65 million years ago. Information from a new species called Vegavis iaai indicates that these birds lived in the Cretaceous and must have survived the Cretaceous/Tertiary (K/T) mass extinction event that included the disappearance of all other dinosaurs. Analysis of the fossil, discovered in Antarctica in 1992, revealed  a new species in the group Anseriformes, which includes ducks and geese. The question of whether relatives of living birds co-existed with non-bird dinosaurs has evoked controversy. Some investigators, using  “molecular clock” models and DNA sequence data as well as the distribution of living birds, have concluded that relatives of living birds must have existed alongside non-avian dinosaurs and survived the mass extinction of dinosaurs at the K/T boundary. Others believe such data are unreliable, that the fossil record shows no evidence of living bird lineages in the Cretaceous, and that relatives of today’s birds evolved after the K/T boundary. “We have more data than ever to propose at least the beginnings of the radiation of all living birds in the Cretaceous,” Clarke says. “We now know that duck and chicken relatives coexisted with non-avian dinosaurs. This does not mean that today’s chicken and duck species lived with non-avian dinosaurs, but that the evolutionary lineages leading to today’s duck and chicken species did.”

A reconstruction by dinosaur artist Michael  Skrepnick shows Vegavis in the foreground  with a duckbill dinosaur in the background (Source: www.ncsu.edu).

 

Fossil record and phylogeny of ornithurine birds (ornithurine = bird-like, as opposed to sauriurine = reptile-like, e.g, Archaeopteryx).
Solid lines show geological ranges of taxa with first and last occurrences shown by squares.
Dashed lines show postulated phylogeny compiled from the literature (Slack et al. 2006).

Calibrating avian evolution -- Slack et al. (2006) described the earliest penguin fossils and analyzed complete mitochondrial genomes from an albatross, a petrel, and a loon. The penguin fossils were from a Paleocene (early Tertiary) formation just above a well-known Cretaceous/Tertiary boundary site. The fossils, in a new genus (Waimanu), provide a lower estimate of 61–62 Ma for the divergence between penguins and other birds and thus establish a reliable calibration point for avian evolution. Combining fossil calibration points, DNA sequences, maximum likelihood, and Bayesian analysis, the penguin calibrations imply a radiation of modern (crown group) birds in the Late Cretaceous. This includes a conservative estimate that modern sea and shorebird lineages diverged at least by the Late Cretaceous about 74 million years ago. It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Pterosaurs also coexisted with early birds. Additional fossils and molecular data are still required to help understand the role of biotic interactions in the evolution of Late Cretaceous birds and thus to test that the mechanisms of microevolution are sufficient to explain macroevolution.

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• most modern bird genera were present by the end of the Miocene (7 million years ago).
• the Pleistocene (beginning 1.5 million years ago) was a time of much climatic & biogeographic change:
• the Bering land bridge between Asia & North America & the rise of Central America linked continents
• vast areas of the Northern Hemisphere were covered with glaciers during several ice ages
• there may have been 21,000 bird species at the beginning of the Pleistocene, but perhaps as few as 10,000 remained at the end

• Penguins in the southern hemisphere
• Auks [family Alcidae] in the northern hemisphere (Darlington 1957).

The distribution of some groups of birds may have been influenced by continental drift (Cracraft 1974). Some examples of taxa where evidence indicates that intercontinental connections influenced present-day distribution include penguins and parrots:

Source: http://www.odsn.de/odsn/services/paleomap/animation.html

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• Penguins (Spheniscidae)
• distribution centered in the southernmost part of the southern hemisphere
• almost certainly had an extensive Cretaceous distribution within Gondwanaland (Cracraft 1974)
• early Tertiary fossil faunas suggest the influence of intercontinental connections

For many years, the consensus has been that the ancestors of the ratite (flightless) birds may have originated in the ancient super-continent of Gondwanaland, then became widely separated as South America, Africa, and Australia drifted off to their present locations during the Mesozoic.  There they evolved into their present-day forms: ostrich, rheas, emu, cassowaries, kiwis, and moas. However, recent evidence indicates that this scenario is likely incorrect:

The prevailing view has been that ratites are monophyletic, with the flighted tinamous as their sister group, suggesting a single loss of flight in the common ancestry of ratites. However, Harshman et al. (2008) conducted phylogenetic analyses of 20 unlinked nuclear genes and found a genome-wide signal that unequivocally places tinamous within ratites, making ratites polyphyletic and suggesting multiple losses of flight. Phenomena that can mislead phylogenetic analyses (e.g., long branch attraction, base compositional bias, discordance between gene trees and species trees, and sequence alignment errors) were eliminated as explanations for this result. The most plausible hypothesis requires at least three losses of flight and explains the many morphological and behavioral similarities among ratites by parallel or convergent evolution. Finally, this phylogeny demands fundamental reconsideration of proposals that relate ratite evolution to continental drift.

Present-day distribution of extant paleognaths. Dark blue = Rheidae (rheas), orange = Tinamidae (tinamous), green = Struthionidae (Common Ostrich), aqua = Casuariidae (cassowaries),
and pink = Apterygidae (kiwis) (Figure from Widrig and Field 2022).

Chronogram of penguin diversification. Nodes A and B indicate 104 and 90 myr. Credibility intervals (95%) are indicated by grey bars at numbered internal nodes. Vertical dashed line indicates the K/T boundary. Periods when Antarctica was ice-covered (black continuous bars) are indicated by shaded grey rectangles. Ocean temperature is based on high-resolution deep-sea oxygen isotope records. The MMCT is indicated by an arrow.

Origin and expansion of penguins -- Classic problems in historical biogeography are where did penguins originate, and why are such mobile birds restricted to the Southern Hemisphere? Competing hypotheses posit they arose in tropical-warm temperate waters, species-diverse cool temperate regions, or in Gondwanaland 100mya when it was further north. To test these hypotheses, Baker et al. (2006) constructed a phylogeny of extant penguins from 5851bp of mitochondrial and nuclear DNA. Their analysis suggests that an Antarctic origin of extant taxa is highly likely, and that more derived taxa occur in lower latitudes. Molecular dating indicates that penguins originated about 71 million years ago (i.e., penguins and albatrosses shared a common ancestor approximately 71 mya) in Gondwanaland when it was further south and cooler (and Antarctica was still attached to Australia and South America, and New Zealand was still relatively close to the supercontinent). Moreover, extant taxa are inferred to have originated about 40 mya (Eocene) when Aptenodytes diverged as the basal lineage, and coincident with the extinction of the larger-bodied fossil taxa as global climate cooled. Baker et al. (2006) hypothesized that, as Antarctica became ice-encrusted, modern penguins expanded via the circumpolar current to oceanic islands within the Antarctic Convergence, and later to the southern continents. Thus, global cooling has had a major impact on penguin evolution, as it has on vertebrates generally. Penguins only reached cooler tropical waters in the Galapagos about 4 mya, and have not crossed the equatorial thermal barrier.

The demise of the larger-bodied putative stem-group taxa near the end of the Eocene about 40 mya coincides roughly with the origin of Antarctic-breeding extant taxa (Aptenodytes and Pygoscelis) in the crown-group, and with the beginning of a general cooling in global climate. This was also approximately when the fish-eating cetaceans evolved, and it has been hypothesized they may have out-competed these larger penguins which probably relied on the same food source. Two abrupt cooling periods resulting in the formation of large ice sheets in Antarctica are associated with the diversification of penguin taxa. The first cooling occurred about 34-25 mya, when Spheniscus, Eudyptes and Eudyptula diverged from the older Antarctic genera. These latter ancestral lineages may have dispersed northward by the newly formed circumpolar current, judging from the occurrence of a Eudyptula fossil in New Zealand about 24 mya. As surface waters in the Southern Oceans continued to cool towards the middle Miocene, and the flow of the circumpolar current around Antarctica intensified, another rapid climate transition, the middle miocene climate transition (MMCT) and subsequent increase in Antarctic ice volume occurred between 14 and 12 mya. The MMCT was accompanied by a second bout of cladogenesis that gave rise to multiple species of extant penguins distributed at even lower latitudes, including tips of southern continents. If this scenario is run backwards in the future, continued global warming might be expected to drive temperate-adapted species out of lower latitudes towards their ancestral distribution, possibly causing multiple extinctions of existing species.

• Parrots (psittacids)

• predominantly pantropical
• relationships between South American and Australian groups likely due to the Gondwanaland fission.

Parrots (Psittaciformes), and other bird orders (e.g., Galliformes; represented by Gallus above), likely diverged about 100 million years ago.
South American parrots (e,g., Pyrrhura, Derptyus, Guaruba, Aratinga, Anodorhyncus, and Ara) diverged from Australian parrots (e.g., Melopsitacus)
about 76 million years ago (Cretaceous-Tertiary boundary) when South America and Australia were moving away from Antarctica (Gondwanaland fission)
(From: Miyaki et al. 1998). .

Geographic Ranges of Birds

The distribution of a species is a consequence of its:

• history
• ecological tolerances (which dictate where it can live),
• the geographical distribution of places satisfying these requirements, &
• how the matching of species to places is modified by factors such as
• barriers to dispersal,
• interactions with other species, or
• chance (Wiens 1991).

• northern limits of several passerines in North America are associated with mean January minimum temperature, duration of the frost-free period, or mean snow depth, e.g.:
• the northern winter range limit of Eastern Phoebes appears to be set by the isotherm at which average minimum January temperature is -4 degrees C

Eastern Phoebe's winter range in the U.S.

• Northern Cardinal - northern range of this ground-foraging seed eater may be set by the persistence of deep snow

Winter range of the Northern Cardinal in the U.S. & Canada

• range limits may be influenced by interspecific interactions, e.g.:
• Boreal Chickadees & Chestnut-backed Chickadees

• habitat requirements may limit ranges, e.g.:
• Kirtland's Warbler is limited to a small area of jackpine in northern Michigan
• and many, many other species of birds

 

• chance may play a role in a bird's distribution, e.g.:
• Cattle Egret

Given these various factors, how are the world's birds distributed across the six primary zoogeographical realms, the Nearctic, Neotropical, Palearctic, Ethiopian (or Afrotropical), Oriental (or Indomalayan), and Australasian?

Evaluating species limits in birds -- Watson (2005) examined sources of data used to diagnose new species and found variation among classes. New species of amphibians were typically diagnosed using external appearance, morphometrics, and external morphology, while reptiles were typically diagnosed using appearance and external morphology. Mammals were generally described using morphometrics, external morphology, and internal morphology, whereas new bird species diagnoses relied on external appearance, morphometrics, and behavior (see figure to the right). Birds were the only group described primarily using external appearance (98%; only one species description did not use plumage characteristics), compared with an overall frequency of 54% for the other three groups combined. Ecological data (distributional range, habitat, and behavior) were used for 62% of new bird descriptions, significantly more than the 14% for the other three classes combined. The use of molecular data was consistent across all four classes; by contrast, behavioral traits (typically vocalizations) were used for amphibians and birds but not for reptiles or mammals.

Sources of data used to diagnose new species of birds (1993 - 2002). Data types: 1, appearance; 2, morphometrics; 3, external morphology; 4, internal morphology; 5, range; 6, habitat; 7, behavior; 8, molecular data; 9, karyology; 10, reproduction. Photograph of the Green-crowned  Brilliant (Heliodaxa jacula) by David M. Watson. Of the 60 new bird species described, there were 7 owls, 7 tyrant flycatchers, 2  hummingbirds, and 1 parrot (see www.csu.edu.au/faculty/sciagr/eis/staff/watson.htm for details).

DNA barcode (base pair sequence) of a Green Heron
(Photo courtesy Biodiversity Institute of Ontario)

Birds and DNA barcodes -- The DNA barcodes (see below for an explanation of DNA barcoding) of 643 North American bird species from the Arctic tundra to the temperate woodlands to the Florida Keys (93% of 690 known breeding species in the U.S. and Canada) have now been evaluated (Kerr at al. 2007). According to Paul Hebert of the Biodiversity Institute of Ontario, analysis has revealed that "there are a number of cases of deep genetic divergences within what are currently called single species." These "cryptic species" are those with unique DNA barcodes but differences of song and plumage so subtle as to make them virtually indistinguishable from some other species. Even though birds may appear very similar to human observers, species with distinct DNA barcodes rarely interbreed. "Did we find concordance between barcode results and conventional taxonomy? The answer is, resoundingly, yes. In 95% of cases, entities recognized as species are barcode distinct," adds Dr. Hebert. Dr. Stoeckle of Rockefeller University says there are about 10,000 recognized bird species today and predicts that, at a global scale, DNA barcoding will distinguish at least 1,000 potential new species. The researchers hope to complete an all-bird DNA inventory by 2011. Given the continent's legions of bird specialists, he says he was surprised by the extent of "hidden diversity" revealed in North America, and by the clear DNA distinctions between species. Dr. Stoeckle cautions that "some pairs of listed species now shown to be DNA twins may be relatively young species and prove different over time." As well, he notes, there is no universal scientific agreement on what defines a species.

The importance of this work to conservation is particularly critical, adds Dr. Hebert. For example, the Solitary Sandpiper, its habitat increasingly under pressure from land development and climate change, was not known previously to have two forms, yet their DNA reveals two distinct groups split about 2.5 million years ago. "How can you develop strategies to preserve highly different genetic entities if you don't know they're there? Our work is providing the first molecular evidence of some of these splits." Perhaps the biggest surprise is that DNA barcoding works as well as it does, that a relatively short code of genes (base pairs) distinguishes species so clearly and there isn't more blurring between species, says Dr. Stoeckle. Barcoding has prompted speculation and theories about mechanisms that strip variation out of species and keep them sharply distinct -- periodic "selective sweeps" -- and the reasons behind them. "This work is raising questions about how evolution works and what species are," he says. So far, the Barcode of Life Data Systems ( www.barcodinglife.org ) has catalogued more than 25,000 species of all types, and over 200,000 individual records.

"New" bird species based on DNA barcode analysis (Kerr et al. 2007).
These 15 species each include two distinct barcode clusters.

DNA barcoding is a technique for characterizing species of organisms using a short DNA sequence from a standard and agreed-upon position in the genome.  DNA barcode sequences are very short relative to the entire genome and they can be obtained reasonably quickly and cheaply.  The cytochrome c oxidase subunit 1 mitochondrial region (COI) is emerging as the standard barcode region for higher animals. It is 648 nucleotide base pairs long in most groups, a very short sequence relative to 3 billion base pairs in the human genome, for example. The ‘barcode’ metaphor is useful though not correct in fine detail. That is, all the products of one type on a supermarket shelf share exactly the same 11-digit barcode that is distinct from all other barcodes. DNA barcodes vary among individuals of the same species, but only to a very minor degree. If the DNA barcode region is effective, the minor variation within species will be much smaller than the differences among species.

Alfred Russell Wallace (1876) studied the world-wide distribution of animals, including birds, and noted that different regions possessed biotas that were, to varying degrees, unique. Based on his analysis, he delineated six such regions, or zoogeographical realms: Nearctic, Palearctic, Neotropical, Ethiopian, Oriental, and Australian. With minor names changes (Figure below), these realms are still recognized as having distinctive assemblages of birds. Each realm has their characteristic birds; avifaunas that represent a mixture of species of various ages & origins. Of course, some birds are found beyond the borders of these realms on Oceanic islands and in Antarctica.

Here's a brief summary of the avifaunas of these realms:

• Palearctic (check this site: Birds of the Western Palearctic)
• Europe, Africa north of the Sahara, & almost all of Asia
• largest region & probably where birds originated
• ~1025 species; most are migratory
• ~69 families, just one endemic (Prunellidae)
• predominant group (numbers of species) is the family Sylviidae (old world warblers, e.g., Greater Whitethroat)
• shares many species with the Nearctic (~13%), Ethiopian (~15%), and Oriental (~22%) regions
• along with the Nearctic make up the Holarctic region
• families endemic to the Holarctic include the loons (Gaviidae), waxwings (Bombycillidae), & auks (Alcidae)

• Nearctic
• North America (north of the tropics) & Greenland
• including over 1 billion acres of boreal forest, the deciduous forests of the eastern U.S. and southeastern Canada, the grasslands of the midwestern U.S. and Canada, and the deserts of the southwestern U.S. and northern Mexico
• low diversity; ~ 750 species of breeding birds
• many species migratory
• predominant families include Parulidae (New World warblers) and Emberizidae
• no endemic families (although the turkey subfamily, Meleagridinae, is nearly endemic)
  

Explosive speciation in Setophaga warblers -- The 27 species of Setophaga wood-warblers represent North America's most spectacular avian adaptive radiation. Setophaga species exhibit high levels of local sympatry and differ in plumage and song, but the group contrasts with other well-known avian adaptive radiations such as the Hawaiian honeycreepers and Galapagos finches in that Setophaga species have differentiated modestly in morphometric traits related to foraging. Instead, sympatric Setophaga tend to partition resources behaviorally and have become a widely cited example of competitive exclusion. Lovette and Bermingham (1999) explored the temporal structure of Setophaga diversification via a phylogeny based on 3639 nucleotides of protein-coding mitochondrial DNA (mtDNA). Comparisons with a null model of random bifurcation-extinction demonstrated that cladogenesis in Setophaga has been clustered non-randomly with respect to time, with a significant burst of speciation occurring early in the history of the genus, possibly as long ago as the Late Miocene or Early Pliocene. In North America, an abrupt rise in temperature & aridity occurred near the Miocene - Pliocene boundary, resulting in a reduction and fragmentation of forest habitats. By the Middle Pliocene, however, the continent-wide distribution of forest habitats was similar to present-day conditions. This sequence of paleoenvironmental changes suggests that the many Setophaga lineages may have initially differentiated allopatrically in the forest refugia of the Early Pliocene, followed by ecological reinforcement of adaptive differentiation during secondary contact in the expanded forests of the Middle Pliocene.

Palm Warbler (Setophaga palmarum)

Phenotypic and genetic variation in the genus Junco. The eight different taxa included in the genetic analyses are shown. Colors indicate breeding ranges and dots represent sampling localities. From the south, clockwise, with sampling locality number in parentheses: Volcano (1), Yellow-eyed (2-11), Red-backed (12, 13), Grey-headed (14, 15), White-winged (16), Pink-sided (17), Oregon (18, 19) and Slate-colored Juncos (20-23). Site 23 corresponds to a wintering locality of the Slate-colored Junco in Alabama.

Postglacial range expansion drives the rapid diversification of the genus Junco -- Pleistocene glacial cycles are thought to have played a major role in the diversification of temperate and boreal species of North American birds. Given that coalescence times between sister taxa typically range from 0.1 to 2.0 Myr, it has been assumed that diversification occurred as populations were isolated in refugia over long periods of time, probably spanning one to several full glacial cycles. In contrast, the rapid postglacial range expansions and recolonization of northern latitudes following glacial maxima have received less attention as potential promoters of speciation. Milá et al. (2007) reported a case of extremely rapid diversification in the songbird genus Junco as a result of a single continent-wide range expansion within the last 10000 years. Molecular data from 264 juncos sampled throughout their range reveal that as the Yellow-eyed Junco (Junco phaeonotus) of Mesoamerica expanded northward following the last glacial maximum, it speciated into the Dark-eyed Junco (Junco hyemalis), which subsequently diversified itself into at least five markedly distinct and geographically structured morphotypes in the USA and Canada. Patterns of low genetic structure and diversity in mitochondrial DNA and amplified fragment length polymorphism loci found in Dark-eyed Juncos relative to Mesoamerican Yellow-eyed Juncos provide support for the hypothesis of an expansion from the south, followed by rapid diversification in the north. These results underscore the role of postglacial expansions in promoting diversification and speciation through a mechanism that represents an alternative to traditional modes of Pleistocene speciation. Recent divergence with fast plumage evolution (since the LGM) has been recently documented in Icterus orioles, redpolls, bluethroats, yellow wagtails, and Yellow-rumped Warblers. However, given the higher number and marked distinctiveness of plumage morphs and the short amount of time involved, the Dark-eyed Junco complex represents an exceptional case of fast plumage diversification. Given the marked differences in plumage characters, sexual selection may have acted as the mechanism of divergence.

Seminar - The ordinary extraordinary junco by Ellen Ketterson

Distribution of nearest congeneric neighbor distances in COI (i.e., cytochrome c oxidase I gene region) for bird species in three biogeographic regions. Distances tend to be higher in the southern Neotropics than in North America and the incidence of species pairs with very low divergence (less than 1% sequence distance) is much higher in North America. Divergence values in the Palearctic are closer to those of the Neotropics than to those in the Nearctic.

Continental patterns of avian diversification -- Causes for the higher biodiversity in the Neotropics as compared to the Nearctic and the factors promoting species diversification in each region have been much debated. The refuge hypothesis posits that high tropical diversity reflects high speciation rates during the Pleistocene, but this conclusion has been challenged. Lijtmaer et al. (2011) investigated this matter by examining continental patterns of avian diversification through the analysis of large-scale DNA barcode libraries. Datasets from the avifaunas of Argentina, the Nearctic, and the Palearctic were analyzed. Average genetic distances between closest congeners and sister species were higher in Argentina than in North America reflecting a much higher percentage of recently diverged species in North America (Nearctic). In the Palearctic, genetic distances between closely related species appeared to be more similar to those of the southern Neotropics. Average intraspecific variation was similar in Argentina and North America, while the Palearctic fauna had a higher value due to a higher percentage of variable species. Geographic patterning of intraspecific structure was more complex in the southern Neotropics than in the Nearctic, while the Palearctic showed an intermediate level of complexity. This analysis suggests that avian species are older in Argentina than in the Nearctic, supporting the idea that the greater diversity of the Neotropical avifauna is not caused by higher recent speciation rates. Species in the Palearctic also appear to be older than those in the Nearctic. These results, combined with the patterns of geographic structuring found in each region, suggest a major impact of Pleistocene glaciations in the Nearctic, a lesser effect in the Palearctic and a mild effect in the southern Neotropics.

In the Nearctic, almost all variable species showed eastern and western lineages hat is consistent with population expansions from glacial refugia in the margins of North America. The eastern and western portions of the Nearctic probably acted as refugia during the early and mid Pleistocene, but were later covered by ice. This is consistent with the fact that the eastern and western lineages within species typically show more than 1.5% divergence. In the Palearctic, three patterns were found and interpreted at least partially as evidence of range expansion from refugia after the retreat of the ice or permafrost that covered much of the northern portion of Eurasia. Finally, in the Neotropics several patterns were found and they appear to reflect various sources of diversification, including the Andes Mountains. These differences once again support the conclusion of a major effect of Pleistocene glaciations in the Nearctic, a less marked and more heterogeneous effect in the Palearctic, and an even milder effect in the southern Neotropics, where other diversification processes may have been as relevant in shaping current diversity.

• Neotropical
• South America (the 'bird continent'), Central America, lowlands of Mexico, & the West Indies
• about 70% of land mass is low, well-watered, & tropical
• easily the greatest bird diversity of all realms with ~ 3700 species (or more than 1/3 of all bird species) & about 31 endemic families (more than twice that of any other realm)
• dominant groups include Trochilidae (hummingbirds, e.g., Sword-billed Hummingbird), Furnariidae (ovenbirds), Formicariidae (related to antbirds; listen to a Short-tailed Antthrush, Chamaeza campanisona), Tyrannidae (tyrant flycatchers), &  Thraupidae (tanagers).

 
Black-faced Antthrush

To learn more about Neotropical birds (and, more broadly, the birds of the world), visit: Cornell Lab of Ornithology Birds of the World Online!

Suboscines and Oscines Of the more than 3,700 species of Neotropical birds, approximately 1,000 species are classified taxonomically as "suboscines." There are only about 50 suboscine species in all of the rest of the world, thus the Neotropics are unusual in harboring so many members of this group. The suboscines are part of the huge order of Passeriformes, or perching birds. Most passerines in the world are true oscines, which means that they have a complex musculature of the syrinx, the part of the trachea that produces elaborate sounds, such as the flutelike songs of various thrushes and solitaires or the warbling of a canary. Suboscines, however, have a considerably less complex syringeal musculature and typically have far more limited singing abilities than true oscines. Neotropical suboscines have undergone two major adaptive radiations, with the tyrant flycatchers, cotingas, and manakins representing one, and the woodcreepers, ovenbirds, true antbirds, ground antbirds, gnateaters, and tapaculos representing the other. No one knows why suboscines have fared so well in the Neotropics, but the reason may simply be historical. For more information about birds of the neotropics, check out John Kricher: A Neotropical Companion: Chapter 12. Neotropical Birds.

 

Summary of passerine bird distribution and basal relationships (Moyle et al. 2006)

Chesser (2004) studied the phylogenetic relationships among New World suboscine birds using nuclear and mitochondrial DNA sequences. New World suboscines were shown to constitute two distinct lineages, one apparently consisting of the single species Sapayoa aenigma (Broad-billed Sapayoa), the other made up of the remaining 1000+ species of New World suboscines. With the exception of Sapayoa, monophyly of New World suboscines was strongly corroborated.

Broad-billed Sapayoa

 

Moyle et al. (2006) used molecular and morphological data to derive a phylogenetic hypothesis for the Eurylaimides, an Old World bird group now known to be distributed pantropically, and to investigate the evolution and biogeography of the group. Phylogenetic results indicated that the Eurylaimides consist of two monophyletic groups, the pittas (Pittidae) and the broadbills (Eurylaimidae sensu lato), and that the broadbills consist of two highly divergent clades, one containing the sister genera Smithornis and Calyptomena, the other containing Pseudocalyptomena graueri, Sapayoa aenigma, the asity genera Philepitta and Neodrepanis, and five Asian genera. Their results indicate that over a ~10 million year time span in the early Tertiary, the Eurylaimides came to inhabit widely disjunct tropical regions and evolved disparate morphology, diet, and breeding behavior. Biogeographically, although a southern origin for the lineage is likely, time estimates for major lineage splitting do not correspond to Gondwanan vicariance events, and the biogeographic history of the crown clade is better explained by Laurasian climatic and geological processes. In particular, the timing and phylogenetic pattern suggest a likely Laurasian origin for the sole New World representative of the group, Sapayoa aenigma.

• Ethiopian (or Afrotropical)
• Africa south of the Sahara, southern Arabia, & Madagascar
• large proportion of desert, grassland, & savanna habitats

• home to ~1800 species of birds
• predominant groups include weaverbirds, shrikes, & larks
• shows strong affinities with the Oriental region at the generic level (~30% of Ethiopian genera also occur in the Oriental region), but not as much at the species level (~2%). This suggests a long period of independent evolution in the two areas (Moreau 1952).
• Over 70 families of land & fresh-water birds breed here, but few (~ 8 in Africa; 5 in Madagascar) are endemic (or nearly so), including: Ostrich (Struthionidae), Hammerhead (Scopidae), Secretary Bird (Sagittariidae) (shown below), Mousebirds (Coliidae), Touracos (Musophagidae), and Helmet Shrikes (Prionopidae).
• The Afrotropical realm also serves as a wintering area for many Palearctic species.

 

(A) Areas where 68 species of Palearctic migrant songbirds winter in sub-Sahara Africa, with darker green indicating a greater number of species.
(B) Areas with the most seasonal patterns of rainfall in sub-Sahara Africa (with darker red indicating greater seasonality), with rainfall peaking at the beginning of the
wintering period for Palearctic migrants (Figure A modified fom Walther and Pirsig 2017 and B modified from Feng et al. 2013).

 
Flock of Red-billed Quelea (one of Africa's most abundant birds)

Species richness of breeding birds endemic to Africa for species with large
(>100 1^o quadrats, 840 species, A) and small (100 1^o quadrats, 756 species, B) range size.
Values range from 2 (light) to 440 (dark) in A and from 0 (light) to 120 (dark) in B
(From: Jetz and Rahbek 2001).

• Broadly, areas with higher levels of energy-related variables such as primary productivity, potential evapotranspiration, solar radiation, temperature, and rainfall tend to have higher species richness. More specifically, birds are most speciose in the forest-dotted crescent around Lake Victoria. Other areas of particular richness run south through the mountains of Kenya, Tanzania, and Malawi and west through the forest–savanna ecotone north of the Congo Basin into the Guinea forests. Areas of lowest richness lie in the Sahel, the Horn of Africa, and the Kalahari, Namib, and Karoo drylands (Brooks et al. 2001).
• Fifty-eight percent of Africa’s resident birds are oscine songbirds (Fjeldså and Bowie 2008), and molecular analyses suggest that songbirds arrived in Africa in the Miocene (40 mya). Songbirds are thought to have originated in the Australasian realm and some investigators have suggested that songbirds reached Africa by way of Asia (Figure above). However, the discovery of several very old songbird lineages in Africa (Picathartidae, or rockfowl and rockjumpers; Beresford et al. 2005) indicate that dispersal of songbirds from Australia to Africa likely occurred earlier the thought possible by the ‘Asian-route’ hypothesis. An alternative hypothesis is that islands in the southern Indian Ocean could have served as ‘stepping-stones’ and provided a more direct route between Australia and Africa (Figure above; Fjeldså and Bowie 2008). In the Neotropical realm, there was a sharp increase in rates of speciation in the Pliocene/Pleistocene that was apparently driven by increasing habitat complexity and altitudinal gradients resulting from the development of the Andes Mountains. No such pronounced increase occurred in Africa. Rather, the widespread lowland rainforests mainly acted as ‘museums’, permitting survival of species, but not promoting speciation (Fjeldså 1994). The diversification and speciation that has occurred in Africa has largely happened at forest/savanna transition zones, with mosaics of savanna and forest generated by a gradual aridification of the continent, and in montane highlands in eastern Africa ( Fjeldså and Bowie 2008).

• Oriental (or Indomalayan)
• India, southeast Asia (Malay Archipelago), Java, Borneo, & the Phillipines
• ~ 2400 species of birds
• of 66 families of land & fresh-water birds resident in this region, only one, the Irenidae (Leafbirds & Fairy Bluebirds), is endemic
• characteristic birds include many pheasants & pigeons, owls, woodpeckers, pittas, hoopoes, barbets, honeyguides, & sunbirds.
• some Oriental groups, e.g., barbets, range as far east as Bali & no further, while the range of several Australian birds (e.g., honey-eaters & cockatoos) range as far west as Lombok (35 km from Bali) but not further. This area of rather abrupt changes in faunas is called Wallace's Line.

 

 
Common Hoopoe

Southeast Asia has numerous geographic islands. The Malay Archipelago, as southeast Asia is known to biogeographers, covers 2,894,0000 square kilometers -- only twice the size of Alaska. Yet the region comprises at least 20,000 islands, of which 13,000 make up Indonesia in a chain 5,000 kilometers long between Asia and Australia. The Indonesian archipelago has not always been so broken up. When the sea level has dropped, as it has several times during the relatively recent past, many of the islands have merged to form a single territory, allowing their wildlife communities to mingle. When the seas have receded again, splitting up the prehistoric forests into fragments once more, each separate sector would follow its evolutionary path in response to its own set of local environmental conditions and selection pressures. Greater diversity and complexity result. When the seas advance again, there will have been a repeated mingling of biotas and more creative tension between disparate communities of animals and plants, which often leads to some extinctions but eventually fosters more speciation. The overall result is an exceptional amount of biotic diversity. Among the endemic species of birds, 94% are confined to a single island or a small group of islands.

Asian Fairy-Bluebird

• Australasian
• Australia, New Zealand, Papua New Guinea, & several small islands in the area
• generally a dry region, only 4.5% rainforest
• about 70% of Australia is desert & in this area only 17 species of birds occur (3% of Australia's avifauna)
• ~ 1600 species in the Australian region (907 in Australia alone, including 642 breeding birds, 162 vagrants, 77 non-breeding birds, and 26 introduced by humans)
• ~64 families of terrestrial & freshwater birds represented, with several unique:
• Cassowaries (Casuariidae) (Learn more about Cassowaries: Part 1, Part 2, Part 3, Part 4).
• Emus (Drommiceidae)
• Kiwis (Apterygidae)
• Megapodes (Megapodiidae)
• Owlet-nightjars (Aegothelidae)
• New Zealand wrens (Acanthisittidae)
• Lyrebirds (Menuridae)
• Scrub-birds (Atrichornithidae)
• Birds of Paradise (Paradisaeidae)
• Bowerbirds (Ptilonorhynchidae)
• Honeyeaters (Meliphagidae)
• Corcoracidae (two species, the White-winged Chough and Apostlebird)

Spatial patterns of avian species richness in Australia across three levels of spatial resolution, from 0.25° grid cells to 1° grid cells (Hurlbert and Jetz 2007). The contemporary richness pattern is well explained statistically by actual evapotranspiration (a measure of water–energy balance), operating both directly and indirectly through plant production (Hawkins et al. 2005).

Australia's Eastern Whipbird on Vimeo 

• Oceanic Islands
• typically support fewer species of land & freshwater birds than equal areas of comparative mainland
• obvious influences on bird diversity on islands are age, topography, size, & distance from nearest source of immigrants
• importance of size & distance was first quantified by MacArthur & Wilson (1967)
• For example, New Zealand (Baker 1991):

• only 65 native species of land & freshwater birds (with an additional 47 species known from fossil remains and 34 species introduced by humans during the past 130 years)
• 2 endemic orders (Apterygiformes or kiwis & Dinornithiformes or moas [extinct]), 3 endemic families (Xenicidae or New Zealand wrens, Callaeatidae or Kokako, huia, & saddleback & Turnagridae or New Zealand thrushes [probably extinct]), and 37 endemic species (57% of native species; 70% if recently-extinct & fossil species are included) 

• avifauna composed largely of elements that dispersed to New Zealand long after the breakup of Gondwanaland
• Australian element, not surprisingly, is dominant - prevailing westerly winds regularly deposit Australian species in New Zealand (e.g., 8 species have successfully colonized New Zealand in the past 150 years)
• other biogeographical elements include Holarctic (just 3 species) & Archaic (endemic taxa with such a long evolutionary history in New Zealand that no close relatives can be identified elsewhere, e.g., kiwis and moas)
• routes of colonization:
• Tasman Sea has been the principle route
• direct route from the Holarctic (e.g., shorebirds & waterfowl)
• Other islands also have (or had) distinct avifaunas, e.g., see 'Hawaii's Honeycreepers'

 

New Zealand's Kiwis  

The avifauna of the islands of Wallacea includes elements of both Indomalayan and Australian origin (Michaux 2010). Of 513 species of breeding land birds in Wallacea, 300 (58%) are endemics and 213 (42%) are non-endemics that also breed outside of Wallacea. As also found in other island biogeography studies, island geography, especially island area, but also isolation and elevation, largely explain the variation in island species richness and endemism in Wallacea (Dalsgaard et al. 2014).

(A) Total species richness on islands in Wallacea. (B) Species richness of regional endemics (only found on islands in Wallacea) in Wallacea.
SUL, Sulawesi (Figure modified a bit from Dalsgaard et al. 2014).

The avifauna of the islands in the tropical Indian Ocean (excluding Madagascar) consists of about 139 species of resident birds (excluding pelagic and introduced species) representing 33 different families of birds. Of these species, 10 species are endemic to the Indian Ocean and 69 are endemic to a single archipelago or island. Most endemic species are in the families Columbidae (pigeons), Psittacidae (parrots), Muscicapidae (thrushes and Old World flycatchers), and Zostertopidae (white-eyes) (Adler 1994). Unfortunately, several of the 139 species of resident birds are now extinct.

The presence of relatively few endemic species of birds on the islands of the tropical Indian Ocean is due to the almost complete absence of any intra-archipelago speciation, likely because the Indian Ocean archipelagos have too few of the large islands needed for such speciation. In addition, some families of birds that are widespread in the Afrotropical and Indomalayan realms, such as Alcedinidae (kingfishers) and Sturnidae (starlings), are either absent or poorly represented on islands in the tropical Indian Ocean. For some families, e.g., kingfishers, this absence may be due the absence of suitable habitat (rivers, streams, or lakes). For other families, reasons for their absence is less clear (Adler 1994).

Avifaunas of islands in the Indian Ocean. The first number below each island’s and group of island’s name is the
number of species of resident breeding birds; the second number is the number of endemic species (Figure modified from Adler 1994).

The islands of the Pacific originated in a variety of ways, including as linear chains of volcanic islands, fragments of continental crust, and obducted portions of adjoining tectonic plates (Neall and Trewick 2008).

Avifaunas of islands in the Pacific Ocean. Numbers below the names of islands indicate, in order, the number of
breeding land birds, number of endemic species, and total number of species including seabirds (Figure modified from Steadman 1995).

The Hawaiian archipelago consists of 45 islands extending across 2450 km of the central Pacific Ocean and is the most remote archipelago on the planet (Juvik and Austring 1979). The Hawaiian Islands once had at least 111 native species of birds, almost all endemic, before humans (Polynesians) arrived about 1000 years ago. Of those 111 species, 55 became extinct after arrival of the Polynesians and are now known only as fossils, and 19 more extinctions occurred after arrival of Europeans (Scott et al. 2001). Of the remaining 37 extant endemic species, 33 are at some risk of extinction. In addition to these endemic species, at least 22 species of seabirds breed on the Hawaiian Islands, and another 54 species of landbirds have been introduced by humans and now breed in Hawaii.

All of Hawaii’s endemic species of birds are thought to have originated from just 20 colonization events, and the many species of honeycreepers (originally more than 50, just 17 remain) are thought to be derived from a single ancestor (Berger 1981, Olson and James 1982). Based on analyses of mitochondrial genomes, Lerner et al. (2011) suggested that Hawaiian honeycreepers are a sister taxon to Eurasian rosefinches (Carpodacus) and that the ancestor of the honeycreepers arrived in Hawaii about 6-7 million years ago. In addition to the honeycreepers, the endemic Hawaiian avifauna includes (or included) several waterfowl, two raptors, a crow (extinct in the wild, but some still live in captivity), and representatives of Old World flycatchers, honeyeaters, and thrushes (Jacobi and Atkinson 1995). The ancestors of these and other endemic species arrived in the Hawaiian Islands beginning about 5 million years ago.

Estimated arrival times (millions of years ago, Mya) of the ancestor of several species and taxa of birds in the Hawaiian Islands
(Price and Clague 2002; except Hawaiian honeycreepers from Lerner et al. 2011).

The islands in the Atlantic Ocean off the coasts of southern Europe and northern Africa are collectively referred to as Macaronesia. This region has 31 principal volcanic islands that are grouped into five archipelagos: Azores, Madeira, Selvagens, Canary Islands, and Cape Verde (Figure below). These archipelagos vary in their distance from the mainland (range = <100 km for the Canary Islands and 1365 km for the Azores), latitude, and age (range = 0.25 – 29 million years) (Hazevoet 1995, Geldmacher et al. 2001, Azevedo and Ferreira 2006). The taxonomic affinities of native bird species suggest that the origin of the extant terrestrial avifauna is largely from the western Palaearctic mainland, but the Cape Verde archipelago, because of its lower latitude and proximity to Africa, has species related to mainland Africa (Hazevoet 1995, Martín and Lorenzo 2001, Clarke et al. 2006). In addition, the avifaunas of the four largest archipelagos (excluding Selvagens) have all reached an equilibrium, with species richness reaching a plateau because rates of colonization and speciation are similar to extinction rates (Valente et al. 2017).

(A) Colonization times of Macaronesian species of landbirds and a map of Macaronesia. The vertical lines to the left indicate the maximum geological ages of the archipelagos.
Filled circles, non-endemic species; unfilled circles, endemic species; unfilled squares, Macaronesian endemic. The Selvagens Islands, although important breeding areas for several species of seabirds,
have only two resident landbirds: Berthelot’s Pipit (Anthus bertheloti) and Common Kestrel (Falco tinnunculus). (B) Estimated n umbers of species over time in each of the archipelagos.
Black lines are estimated median values and the colored areas show the 2.5th–97.5th percentiles. Gray dashed line, pre-human diversity; black dashed line, present diversity (excluding extinct species).
Time before present is in millions of years (Figures from Valente et al. 2017).

The West Indies consist of three groups of islands: (1) the Greater Antilles, including Cuba, Hispaniola, and Puerto Rico, are old fragments of continental crust that originally formed as islands closer to present-day Central America and carried to their present locations by plate movements, (2) the Bahama islands are low-elevation islands located north of the Greater Antilles and southeast of Florida, and (3) the Lesser Antilles were created by a series of volcanoes, some still active, where the South American Plate is being subducted under the Caribbean plate. Bird species richness of the West Indies is low compared to the nearby continents, likely because of the limited dispersal abilities of many avian taxa (Ricklefs and Bermingham 2001). Water barriers reduce the likelihood of colonization by birds that rarely move beyond forest borders like most tropical suboscine passerines and woodpeckers (Terborgh 1973, Terborgh et al. 1978).

Of the 243 breeding species in West Indies, 176 (72%) are endemics and 67 (28%) non-endemics (Dalsgaard et al. 2014). The main pathways of immigration into the islands have been from the south (the northern coast of South America and through the Lesser Antilles), from the west (Central America and into the Greater Antilles), and from the north (Florida). Although South America contains a larger species pool of potential immigrants and the Lesser Antilles are close to the coast of South America, more species of birds in the West Indies originated in North and Central America (Bond 1963). However, species that have invaded the West Indies from South America have tended to move further north than species that emigrated from North and Central America. As is typically the case, the larger islands in the West Indies have more landbird species and more endemic species of birds.

A) Total species richness on islands in the West Indies. (B) Species richness of regional endemics, i.e., only found on islands
in the West Indies. FL, Florida; PR, Puerto Rico; SA, South America (Figure modified from Dalsgaard et al. 2014).

Seminar - Challenges and opportunities for Caribbean endemic bird conservation

The islands of the Southern Ocean can be divided into older islands with a continental origin (e.g ., Falkland Islands, South Georgia, Auckland and Campbell Islands), and younger, volcanic islands (e.g., most islands in the southern Indian Ocean). Islands in the Southern Ocean have cool, wet, and windy climates. The islands are covered in tundra vegetation, ranging from scattered dwarf plants to grasslands, herbfields, and bogs. Vegetation in coastal areas includes tussock grasses, graminoids, and herbs; more upland areas are often covered with cushion-forming angiosperms and mosses. Vascular plant species richness ranges from zero (Bounty Islands) to 188 (Auckland Islands), and insect species richness varies from six (McDonald Island) to more than 200 (Auckland Islands) (Bergstrom and Chown 1999).

With the exception of the Falkland and Chatham islands, most islands in the Southern Ocean have few or no breeding landbirds. In addition, the Southern Ocean islands have few endemic species. The few breeding songs generally show affinities to the nearest mainland areas. In contrast to the few breeding landbirds, the Southern Ocean islands are the primary nesting areas for numerous species of seabirds. The productivity of the southern oceans provides abundant food for breeding seabirds.

Islands of the Southern Ocean. Numbers below the names of the islands indicate the number of breeding landbirds, number of endemic species,
and total number of breeding birds. Most birds breeding on these island are penguins, albatrosses, petrels and prions,
shearwaters, storm-petrels, skuas, and gulls and terns (Numbers from Shirihai 2007; Figure modified from Angel et al. 2009).

(A) An artist's impression of H. moorei attacking the extinct New Zealand moa. Evidence of eagle strikes are preserved on skeletons of moa weighing up to 200 kg. (Artwork: John Megahan.) (B) Comparison of the huge claws of H. moorei with those of its close relative  Hieraaetus morphnoides, the “little” eagle. The massive claws of H. moorei could pierce and crush bone up to 6 mm thick under 50 mm of skin and flesh.

Ancient DNA Tells Story of Giant Eagle Evolution -- For reasons not entirely clear, when animals make their way to isolated islands, they tend to evolve relatively quickly toward an outsized or pint-sized version of their mainland counterpart. One avian giant was found in New Zealand:  Haast's eagle (Harpagornis moorei), with a wingspan up to 3 meters. Though Haast's Eagle could fly,  its body mass (10–14 kilograms) pushed the limits for self-propelled flight. As extreme evolutionary examples, large island birds can offer insights into the forces and events shaping evolutionary change. Bunce et al. (2005) compared ancient mitochondrial DNA extracted from Haast's Eagle bones and found that the extinct raptor underwent a rapid evolutionary transformation that belies its kinship to some of the world's smallest eagle species. Their analysis places Haast's Eagle in the same evolutionary lineage as a group of small eagles in the genus Hieraaetus. Surprisingly, the genetic distance separating the giant eagle and its smaller cousins from their last common ancestor is relatively small.       Using  molecular dating techniques, Bunce et al. (2005) proposed a divergence date of  0.7–1.8 million years ago. The increase in body size—by at least an order of magnitude in less than 2 million years—is remarkable, Bunce et al. (2005) argue, because it occurred in a species still capable of flight. The absence of mammalian competitors may have precipitated the rapid morphological shift. Haast's eagle, the authors wrote, “represents an extreme example of how freedom from competition on island ecosystems can rapidly influence morphological adaptation and speciation.” -- Source: (2005) Ancient DNA Tells Story of Giant Eagle Evolution. PLoS Biol 3(1): e20.

Haast's Eagle - The King of All Eagles

Avifaunas of the various zoogeographic realms represent a mixture of species of various ages & origins. The mobility of many (but not all) birds, plus their proclivity to migrate, has allowed the movement of some groups between realms - some very long ago, others more recently. And, once a species arrives in a new area, adaptive radiation often generates new species. This combination of avian mobility (or lack thereof) and adaptive radiation has created avifaunas that represent complex mosaics (Gill 1995). Briefly, the avifaunas of the major zoogeographic realms can be described as follows:

• Palearctic
• many genera shared with the Nearctic, Ethiopian, & Oriental regions indicating much dispersal
• geographic 'barriers' between these regions include:
• the Sahara desert (Ethiopian)
• the Himalayas (Oriental) (viewed from space in photo to the right)
• the Bering Sea (Nearctic)
• relatively low species richness, probably due to cold climate & large areas of homogeneous habitat (taiga)

 

• Nearctic
• species richness, compared to most other realms, is relatively low. Contributing factors include:
• birds entering from Siberia must pass through areas of tundra & cold coniferous forest (with no access at all during periods of glaciation)
• tropic-adapted species from the south are faced with an adverse climatic gradient. For example, few South American birds have colonized the deciduous forests of the eastern United States (one hummingbird - the Ruby-throated Hummingbird - & two tanagers - Summer and Scarlet tanagers).
• low species richness in North American deciduous forests because:
  • they formed a continuous block (restricting opportunities for speciation)
  • they have been compressed during glacial maxima

Geographic variation in the richness of breeding terrestrial bird species in the Nearctic and northern Neotropics. The heavy dashed lines in southern Mexico distinguish cells classified as Nearctic and cells classified as Neotropical. Numbers represent the number of bird species in each cell (Hawkins et al. 2003).

Deciduous forest may have barely existed in the southern USA at the Last Glacial Maximum (LGM). Contrary to most of the earlier interpretations, it now seems inappropriate to show any significant area of deciduous forest in the eastern US for the LGM. Current work by S. Jackson (Northern Arizona University), Eric Grimm (Illinois State Museum), and Bill Watts suggests that even in the south there was very little broad-leaved forest at the LGM, with perhaps only isolated pockets of deciduous forest that were surrounded by coniferous vegetation. These deciduous forest pockets at the LGM may have been confined to moister microsites, such as stream gullies (Ritchie 1982). For example, spruce forest has been found to have been growing in Louisiana at the LGM. Tallis (1990) also maps a south-eastern pine forest that extending from about 33°N down to the Gulf coast and northern Florida, and suggests that it would generally have been fairly open in structure. Source: http://www.soton.ac.uk/~tjms/namerica.html

Eastern U.S. - 18,000 years ago Source: http://www.esd.ornl.gov/projects/qen/NAL2215.gif & http://www.esd.ornl.gov/projects/qen/nercNORTHAMERICA.html

• avifauna appears to be composed of six elements (Mayr 1946):
• 'Cosmopolitan' - 'mobile' groups with world-wide distributions, including hawks (Accipitridae), swifts (Apodidae), woodpeckers (Picidae), & nightjars (Caprimulgidae)
• 'Panboreal' (or Holarctic) - groups found throughout the Palearctic-Nearctic, including loons (Gaviidae) & some shorebirds
• 'Pan-American' (or Neotropical) - groups that originated in South America, including hummingbirds (Trochilidae), tyrant flycatchers (Tyrannidae), and tanagers (Thraupinae)

• 'Pantropical' - groups with undetermined origins in the southern continents, including parrots (Psittacidae)
• 'Old World'  (or Palearctic):
• early colonizers, including cranes, pigeons, cuckoos, owls, crows, & some thrushes
• later colonizers, including kingfishers, jays, titmice, & some cardueline finches
• recent colonizers, including the barn owl, some swallows, some thrushes, kinglets, & shrikes
• 'Nearctic' - groups that likely originated in North America, including grouse, turkey, wrens, waxwings, & warblers (Parulidae) 

• Pleistocene climatic cycles may have precipitated much speciation, particularly at mid- & high latitudes (Mengel 1964, Selander 1971). This paradigm was challenged based on a review of mtDNA sequence divergences (Klicka and Zink 1997). This review suggested that only 11 of 35 assayed pairs of sister species date to Quaternary separations. Subsequently, Avise and Walker (1998) suggested that divergence of many groups may have started prior to the Pleistocene, but divergence to the species level was promoted by the Pleistocene glaciation.

• a major effect of the southward extensions of the glaciers was to separate many wide-ranging forest/woodland species into eastern & western populations on either side of the prairie grassland belt. Examples of groups within which speciation may have occurred during this time are the:
• flickers (Colaptes spp.; Mayr 1942)
• juncos (Junco spp.; see 'Postglacial range expansion drives the rapid diversification of the genus Junco' above & bluebirds (Sialia spp.) (Rand 1948)
• warblers (Setophaga & Vermivora spp.; Mengel 1964 - but see 'Explosive speciation in Setophaga warblers' above)
• mtDNA evidence suggests that other species were likely confined to single small populations during the Pleistocene &, following retreat of the Wisconsin glacier, expanded rapidly throughout much larger ranges, e.g, Downy Woodpecker, Common Grackle, Red-winged Blackbird, Black-capped Chickadee, & Song Sparrow (Avise 2000).

(A) Male Downy Woodpecker (Picoides pubescens) (photograph by Peter de Wit; Wikimedia Commons).
(B) A possible scenario for dynamic range shifts at high latitudes responding to glaciations by contracting (t2) and
then expanding (t1) during more favorable times. (C) Variation in historical population size for Downy Woodpeckers
through time (From Toews 2015).

Few endemic species of birds are found in the Nearctic and the Palearctic. One important reason for this is that climates in
the northern hemisphere have changed dramatically since the Last Glacial Maximum (LGM; 21,000 years ago). (A) Climate-change velocity
(rate of movement of climatic conditions over the Earth’s surface) since the LGM. Velocity is highest in northeastern
North America (Nearctic) and north-central Eurasia (Palearctic), in and near the areas that were glaciated (delimited by black lines).
(B) Proportion of bird species that are endemic throughout the world. Areas where climate-change velocities have been highest are also the
areas with the fewest endemic species, likely due to species extinctions as well as incomplete range filling. Areas with greater
proportions of endemic species are also the areas where climates have exhibited little or no changes since the LGM. Note also
that many of the areas with high proportions of endemic species are islands (Figures from Sandel et al. 2011).

A, Summer pattern of species richness across North America on the basis of expected number of species over three randomly chosen Breeding Bird Survey routes per 20,000-km2 grid cell. B, Spatial pattern of normalized difference vegetation index (NDVI) in June at 1-km resolution. C, Winter pattern of species richness across North America on the basis of expected number of species over one randomly chosen Christmas Bird Count circle per 20,000-km2 grid cell. D, Spatial pattern of NDVI in December at 1-km resolution (From: Hurlbert and Haskell 2003).

• Ethiopian (Afrotropical)
• strong affinities with the Oriental realm; many Palearctic species winter south of the Sahara desert

Source: http://www.rbge.org.uk/research/russcis/rnpsiberia.htm

• similar latitude to Neotropical realm, but fewer than half as many species:
• less tropical forest & generally much drier than the Neotropics
• few mountain ranges
• endemic families generally contain relatively few species, e.g.:
• 1 ostrich (Struthionidae)
• 1 hamerkop (Scopidae)
• 1 shoe-billed stork (Balaenicipitidae)
• 1 secretarybird (Sagittariidae)
• 6 mousebirds (Coliidae)
• 8 woodhoopoes (Phoeniculidae)
• 44 helmet shrikes (Prionopidae)
• 23 turacos (Musophagidae)

 
Ancient African birds

Lake Nakuru's flamingoes
 

Turacos are uniquely African, with 23 species recognized by most authorities. The forest-living species are undoubtedly among the most spectacularly colorful of birds, while the savanna-dwellers (known as "go-away birds" because of a well-known call, a harsh "kay-waaay") are predominantly grey in plumage. In South Africa, these birds are better known as louries. All are frugivores, specializing in fruit (particularly figs) and sometimes feeding on leaves, buds and flowers. They are usually gregarious, and frequently associate with parrots, hornbills and barbets, with individuals and groups often returning day after day to the same fruiting tree, until the crop is exhausted.

White-bellied Go Away Bird

• Oriental (Indomalayan)
• closest affinities to tropical Africa, but linkages to Palearctic & Australian faunas as well. The Himalayas represent a boundary between Oriental & Palearctic regions; water separates the Oriental & Australian regions.
• only one endemic family (Irenidae), but another nearly so (Eurylaimidae); pheasants (Phasianidae) have undergone considerable radiation

• boundary between Oriental & Australasian realms is Wallace's Line; more recent work indicates that the 'line' runs roughly between Celebes & the Moluccas (~600 km east of Wallace's Line & known as Weber's Line

   

Birds & the Beetles -- Batrachotoxins are neurotoxic steroidal alkaloids first isolated from a Colombian poison-dart frog. In 1992, the toxic principle from feathers and skin of birds in the genus Pitohui, endemic to New Guinea, was isolated and, remarkably, proved to be mainly a batrachotoxin (BTX). BTXs were later found in New Guinea toxic birds of the genus Ifrita. On a weight basis, the batrachotoxins are among the most toxic natural substances known, being 250-fold more toxic than strychnine. It is believed that such toxins provide some protection against the birds' natural enemies, such as parasites and predators, including humans. Neither poison-dart frogs or birds are thought to produce the toxins de novo, but instead they likely sequester them from dietary sources. Dumbacher et al. (2004) described the presence of high levels of batrachotoxins in a little-studied group of beetles, genus Choresine (family Melyridae). These small beetles and their high toxin concentrations suggest that they might provide a toxin source for the New Guinea birds. Stomach content analyses of Pitohui birds revealed Choresine beetles in the diet, as well as numerous other small beetles and arthropods. The family Melyridae is cosmopolitan, and relatives in Colombian rain forests of South America could be the source of the batrachotoxins found in the highly toxic Phyllobates frogs of that region.      The Blue-capped Ifrita (Ifrita kowaldi; shown to the right) is called Nanisani by local villagers. Nanisani is also the word used to describe the tingling and numbing sensation of the lips and face that results from contacting both beetles and bird feathers (Photo Source: Smithsonian National Zoological Park).

A Choresine pulchra beetle with an insert showing  glandular vesicles.

 
Jack Dumbacher and Hooded Piohuis

• Australasian
• Long history of isolation from other land masses
• 16 families endemic (or nearly so); of 308 passerine species, 80% are 'old endemics' belonging to lineages that likely originated & radiated in Australia & New Guinea
• Some evidence that the parvorder Corvi began an evolutionary radiation in Australia about 55-60 million years ago (Sibley and Ahlquist 1985) & gave rise to:
• Superfamily Menuroidea
• Australian treecreepers (Climacteridae)
• lyrebirds (Menuridae)
• bowerbirds (Ptilonorhynchidae) (check this video about the Vogelkop Bowerbird)
• Superfamily Meliphagoidea
• fairywrens & grasswrens (Maluridae)
• honeyeaters & Australian chats (Meliphagidae)
• Thornbills and allies (Acanthizidae)
• Superfamily Corvoidea
• Australian robins (Petroicidae)
• logrunners (Orthonychidae)
• pseudo-babblers (Pomatostomidae)
• diverse set of other birds:
• crows & jays (Corvidae)
• birds of paradise (Paradisaeidae)
• wood-swallows, Australian magpies, butcherbirds, & currawongs (Artamidae)
• magpie larks (Grallinidae)
• bell magpies (Cracticidae)
• whistlers, shrike-tit, thick heads, & pitohuis (Pachycephalidae)
• This particular scenario is not universally accepted. However, it's apparent that many Australasian species evolved in Australia & nearby areas.

Vogelkop Bowerbirds  

 
Bowerbirds - David Attenborough

Formation of New Guinean avian diversity across barriers and along elevational gradients by Knud Andreas Jonsson

Seminar - Poisonous birds and other stories of New Guinea fieldwork by Jack Dumbacher

• Neotropical
• large number of endemics suggests an ancient & distinctive evolutionary history (Mayr 1964)
• some endemic families have undergone extensive evolutionary radiation & contain many species, e.g.:
• hummingbirds (Trochilidae) - 341 species
• ovenbirds (Furnariidae) - 242 species

• antbirds, antshrikes, antwrens, antvireos, bushbirds, fire-eyes, & bare-eyes (Thamnophilidae) - 208 species
• cotingas, bellbirds, becards, cocks-of-the-rock (Cotingidae) - 79 species
• antthrushes & antpittas (e.g., Masked Antpitta) (Formicariidae) - 56 species
• manakins (Pipridae) - 52 species
• woodcreepers (Dendrocolaptidae) - 52 species
• puffbirds (Bucconidae) - 33 species

• tapaculos (Rhinocryptidae) - 30 species
• jacamars (hear a Rufous-tailed Jacamar) (Galbulidae) - 17 species

Rufous-tailed Jacamar

Photograph courtesy Dr. Russell Barrow

 

Common Potoo  

• other endemic families have undergone little radiation, e.g.:
• potoos (Nyctibiidae) - 6 species
• seedsnipes (Thinocoridae) - 4 species
• trumpeters (Psophiidae) - 3 species
• plantcutters (Phytotomidae) - 3 species
• hoatzin (Opisthocomidae) - 1 species (shown to the right)
• oilbird (Steatornithidae) - 1 species
• in addition to these endemics, several groups are more recent arrivals from the Nearctic: vultures (Cathartidae), pigeons (Columbidae), jays (Corvidae), wrens (Troglodytidae), thrushes (Turdinae), blackbirds (Icterinae), & finches (Fringillidae)
• several other groups have pantropical distributions, including cuckoos (Cuculidae), parrots (Psittacidae), barbets (Capitonidae), & trogons (Trogonidae)
• Neotropical forests are home to nearly 700 genera of birds.

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