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.
Bird species richness in the Western Hemisphere (Hawkins et al. 2006).
Bird species diversity in New York state
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.
Loon-like toothed bird Hesperornis regalis swims through the Cretaceous sea
(Painting by Dan Varner; source: www.dmr.nd.gov/ndfossil/Education/trunks/Trunk%20030609.html)
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):
Evidence for the Extant Avian Radiation in the Cretaceous -- Clarke
et al. (2005) provide apparent evidence that cousins of living birds
with dinosaurs more than 65 million years ago. Information from a new
iaai indicates that these birds lived in the Cretaceous and
have survived the Cretaceous/Tertiary (K/T) mass extinction event that
included the disappearance of all other dinosaurs. Analysis of the
discovered in Antarctica in 1992, revealed a new species in the
Anseriformes, which includes ducks and geese. The question of whether
of living birds co-existed with non-bird dinosaurs has evoked
Some investigators, using “molecular clock” models and DNA
data as well as the distribution of living birds, have concluded that
of living birds must have existed alongside non-avian dinosaurs and
survived the mass extinction of dinosaurs at the K/T boundary. Others believe
data are unreliable, that the fossil record shows no evidence of living
bird lineages in the Cretaceous, and that relatives of today’s birds
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.”
Skrepnick shows Vegavis in the foreground
with a duckbill dinosaur in the background
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.
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:
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.
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 (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:
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),
|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.
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.
The 'original' zoogeographical realms (Wallace 1876).
Currently recognized zoogeographical realms and their approximate boundaries (Newton and Dale 2001).
Here's a brief summary of the avifaunas of these realms:
|Explosive speciation in Dendroica warblers -- The 27 species of Dendroica wood-warblers represent North America's most spectacular avian adaptive radiation. Dendroica 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 Dendroica species have differentiated modestly in morphometric traits related to foraging. Instead, sympatric Dendroica tend to partition resources behaviorally and have become a widely cited example of competitive exclusion. Lovette and Bermingham (1999) explored the temporal structure of Dendroica 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 Dendroica 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 Dendroica 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.||
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
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.
To learn more about Neotropical birds, visit: Cornell Lab of Ornithology Neotropical Birds Online!
Suboscines and Oscines
Of the more than 3,700 species of Neotropical
1,000 species are classified taxonomically as "suboscines." There are
about 50 suboscine species in all of the rest of the world, thus the
are unusual in harboring so many members of this group. The suboscines
are part of the huge order of Passeriformes, or perching birds. Most
in the world are true oscines, which means that they have a complex
of the syrinx, the part of the trachea that produces elaborate sounds,
such as the flutelike songs of various thrushes and solitaires or the
of a canary. Suboscines, however, have a considerably less complex
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
one, and the woodcreepers, ovenbirds, true antbirds, ground antbirds,
and tapaculos representing the other. No one knows why suboscines have
fared so well in the Neotropics, but the reason may simply be
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.
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.
Flock of Red-billed Quelea (one of Africa's most abundant birds)
Photo by Doug Jansen
Pied and Woodland kingfishers
African birds feeding on flying ants
Avian species richness in the Indomalayan realm -- Species richness map overlaid by the breeding ranges of 2406 bird species in east Asia. Bird species richness was highest at the base of the Indochina Peninsula and lowest in northern Siberia, the Gobi and Taklimakan deserts and the Tibetan Plateau. Islands had lower bird species richness than adjacent areas in mainland Asia (Ding et al. 2006).
Ding et al. (2006) suggested that primary productivity is the key factor underpinning patterns of bird species richness in east Asia. Primary productivity sets the upper limits of the capacity of habitats to support bird species. In isolated areas such as islands and peninsulas, however, BSR might not reach the richness limits set by primary productivity because the degree of isolation and area size also can affect species richness. Other factors, such as spatial heterogeneity, biotic interactions, and perturbations, may also affect species richness. However, their effects are secondary and are not as strong as primary productivity, isolation, and area size.
|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.||
|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
Common Koel, Bangkok, Thailand
New Zealand's Kiwi
Pacific birds rewrite evolutionary textbook-- Evolutionary biologists have long assumed that species in island-rich areas
such as the Pacific Rim
diverge and evolve in a series of 'stepping-stone' dispersals from one island to the next. But a new analysis of the family tree of tropical Pacific
birds suggests that this cherished assumption is not true. Filardi and Moyle (2005) analysed DNA from a host of bird species from the family
Monarchidae, commonly called Monarch flycatchers. They found that the species seem to have colonized the area not in a series of separate
stepping-stone excursions from continental land masses, but in a single, even spread across all Pacific archipelagos. The researchers support their
conclusion by pointing out that, of the six different species groups that are confined to a single island chain, all are embedded within a group, or
genus, called Monarcha. This genus is spread across the entire tropical Pacific, showing that all of these remote species arose from a single lineage.
What's more, the authors point out, some species show evidence of having recolonized continental areas such as Australia - contrary to the previous
idea that that species colonize island chains only by moving away from continents.
Bird drawings are roughly to scale and illustrate some of the marked morphological differentiation between island endemics that
has complicated the evolutionary interpretation of the group. Colored circles indicate three classes of node age. Branch lengths are
not to scale. Large hatching outlines the distribution of Clytorhynchus and small hatching outlines the range of Monarcha cinerascens.
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
version of their mainland counterpart. One avian giant was found in New
Zealand: Haast's eagle (Harpagornis moorei), with a
up to 3 meters. Though Haast's Eagle could fly, its body mass
kilograms) pushed the limits for self-propelled flight. As extreme
examples, large island birds can offer insights into the forces and
shaping evolutionary change. Bunce et al. (2005) compared ancient
DNA extracted from Haast's Eagle bones and found that the extinct
underwent a rapid evolutionary transformation that belies its kinship
some of the world's smallest eagle species. Their analysis places
Eagle in the same evolutionary lineage as a group of small eagles in
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. (Check the short video accessible at: http://tvnz.co.nz/view/news_technology_story_skin/467281)
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:
Map of species richness among equal area grid cells in the full data set (3,036 taxa) of Palearctic songbirds.
Maximum richness shown in deep rufous and minimum in dark blue. Scores grouped into 32 color-scale classes of
approximately equal frequency. Classes range from 1–3 species per grid cell (blue) to 128–307 (rufous); also a single grid cell
with maximum score (316 species, in northeast Myanmar [Burma]) in red (Roselaar et al. 2007). Most 'hotspot' regions are located
in mountainous regions.
Geographic variation in the richness of bird species in the former USSR. The hatched area in the upper left represents an area classified as the western Palearctic (Hawkins et al. 2003).
The Western Palearctic Avifauna (Blondel and Mourer-Chauviré 1998) -- Compared with that of the two other large forested regions of the Northern Hemisphere (eastern North America and eastern Asia), the bird fauna (and particularly forest avifauna) of the western Palearctic is relatively species poor. Controlling as much as possible for the size of areas, Mönkkönen and Viro (1997) have shown that the western Palaearctic (including North Africa) has 50% fewer forest-associated bird species than eastern Asia and 40% fewer than eastern North America. Europe is similar in size to China (9 500 000 km2, including Manchuria), but European species richness (about 500 bird spp.) is only about half that reported for China. In the western Palaearctic, less than half of the terrestrial avifauna is associated with forest compared with two-thirds in eastern North America and eastern Asia.
Large and repeated habitat changes during the Pleistocene have undoubtedly accelerated the extinction rates of birds of the western Palearctic, just as they did for plants and large mammals in North America. Comparative analyses using molecular phylogenies of 11 lineages of North American songbirds also indicate a general decrease in rates of species diversification during the Pleistocene. However, molecular evolutionary trees cannot distinguish between reduced speciation rates (e.g. as a consequence of progressive niche filling through evolutionary time) and higher extinction rates as the cause of net changes in diversification rates.
Assuming similar rates of speciation over the whole Northern Hemisphere during the Pleistocene, the relative impoverishment of the western Palearctic bird fauna (compared with the two other regions of the Northern Hemisphere) could be caused by higher extinction rates in the western Palearctic, because there was no connection with the tropical biomes further south. In contrast to those of the western Palearctic, the extant bird faunas of both northeastern North America and eastern Asia share many species in common with southern tropical regions. For example, 76% of passerine species breeding in North America have either conspecific populations or congeneric species that breed in the Neotropics. In eastern Asia, two orders and nine families are tropical, whereas Afro-tropical influence in the fauna of the western Palaearctic is negligible.
The most likely explanation for these differences is that the biota of both eastern North America and eastern Asia remained connected to the tropics over the whole Tertiary–Quaternary, making it possible for a continuous interchange between tropical and temperate avifaunas. In contrast, the massive east–west oriented barriers (mountain ranges, seas and large desert belts) ‘trapped' biota of the western Palaearctic in their southern refugia during glacial periods, preventing them from finding refuge in tropical regions further south, and preventing tropical species from colonizing northern regions. Since the Pliocene, the Sahara desert has never been sufficiently forested to provide a dispersal corridor for forest birds between the Afro-tropics and Eurasia.
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||
Source: http://www.esd.ornl.gov/projects/qen/NAL2215.gif &
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).
Hamerkop (Scopus umbretta)
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
|Birds & the Beetles --
neurotoxic steroidal alkaloids first isolated from a Colombian
frog. In 1992, the toxic principle from feathers and skin of birds in
genus Pitohui, endemic to New Guinea, was isolated and, remarkably,
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
against the birds' natural enemies, such as parasites and predators,
humans. Neither poison-dart frogs or birds are thought to produce the
de novo, but instead they likely sequester them from dietary sources.
et al. (2004) described the presence of high levels of batrachotoxins
a little-studied group of beetles, genus Choresine (family Melyridae).
These small beetles and their high toxin concentrations suggest that
might provide a toxin source for the New Guinea birds. Stomach content
analyses of Pitohui birds revealed Choresine beetles in the diet, as
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
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
Jack Dumbacher and Hooded Piohuis
Bowerbirds - David Attenborough
Escaped From Australasia, Conquered Rest of World - That
male cardinal singing his heart out in your backyard has ancestors that
left the neighborhood of Australia 45 million years ago. A
study of DNA from songbirds and their relatives by Barker et al. (2004)
shows that these birds, which account for almost half of all bird
did not originate in Eurasia, as previously thought. Instead, their
escaped from a relatively small area—Australasia (Australia, New
and nearby islands) and New Guinea—about 45 million years ago and went
on to populate every other continent save Antarctica.
The movement of
Guinea plate between 60 (a) and 20 (b) million years
(Mya). When New Zealand
The order Passeriformes, or perching birds, includes all songbirds, such as robins, cardinals, blackbirds, house sparrows, house finches and crows. The group is further divided into birds that must learn their songs “true songbirds” (oscines) and those with the innate ability to sing the “correct” song. True songbirds account for 4,580 of the 6,000 known Passeriformes species. The true songbirds are currently divided into two groups: Passerida (3,477 species, among them many familiar backyard species) and Corvida (1,103 species, including crows and ravens).
The two groups of true songbirds were thought to have separate origins, with Corvida originating in Australasia and the Passerida in Eurasia. The Passerida then supposedly spread from Eurasia to Africa, Australasia and the New World. But in examining the DNA sequences of two genes in all but one family (a closely related group, such as “crows and jays” or “warblers”) of passerine birds, Barker et al. (2004) made a startling discovery. “It was thought that the Passerida arose in Eurasia about 40 million years ago,” said Barker. “But we found that these birds fall into a group within the Corvida. That means all songbirds trace their origins to Australasia and New Guinea.”
The Passerida differ from the Corvida because the Passerida somehow made it out of Australasia and New Guinea and onto the Asian mainland long before the Corvida, Barker said. Asia and Australasia are carried on separate plates in the Earth’s crust, and for many millions of years those plates were far apart. Around 45 million years ago, the ancestors of the Passerida dispersed to Asia—over more than 600 miles of open ocean--long before these two plates approached one another (as shown on map with locations of the continents 45 mybp). For some reason, however, ancestors of the Corvida didn’t make it until about 25 million years later, or 20 million years before today. At that time, Asia and Australia were much closer to each other, and island chains that could have allowed the Corvida ancestors to “island hop” to the mainland appeared, Barker said.
“There are many endemic Corvida birds on the
island of Lombok but very few on Bali, the next island to the west,”
Barker. “And, sure enough, the line separating the Asian plate from the
Australasian plate runs between Bali and Lombok.
Photo © Arthur Grosset
Photograph courtesy Dr. Russell Barrow
Birds of Peru
Rainforest slide show
Bird Biogeography II
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Atlas of the Ice Age Earth
Geology: Plate Tectonics
Glaciers may not have driven modern bird evolution
and the Sea
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