An updated version of these notes can be accessed from a new "Avian Biology' page
The Class Aves includes two superorders:
Loon-like toothed bird Hesperornis regalis swims through the Cretaceous sea.
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 coexisted
with dinosaurs more than 65 million years ago. Information from a new species
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.”
Skrepnick shows Vegavis in the foreground
with a duckbill dinosaur in the background
The distribution of some groups of birds has likely been influenced by continental drift (Cracraft 1974). Some examples of taxa where evidence indicates that intercontinental connections influenced present-day distribution include:
Geographic Ranges of Birds
The distribution of a species is a consequence of its:
Given these various factors, where are the world's birds located?
There are now ~9700 species occupying the six zoogeographical
realms: Nearctic, Neotropical, Palearctic, Ethiopian (or African), Oriental,
|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).
Of course, some birds also occur beyond the borders of these realms on Oceanic islands and on Antarctica. Each realm & many islands have their characteristic birds; avifaunas that represent a mixture of species of various ages & origins.
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.||
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.
Photo by Doug Jansen
|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.||
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.
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:
|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 &
|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 -- 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
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 comprehensive
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 species,
did not originate in Eurasia, as previously thought. Instead, their ancestors
escaped from a relatively small area—Australasia (Australia, New Zealand
and nearby islands) and New Guinea—about 45 million years ago and went
on to populate every other continent save Antarctica.
The movement of the Australia/New
Guinea plate between 60 (a) and 20 (b) million years ago
(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 Indonesian
island of Lombok but very few on Bali, the next island to the west,” said
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
Bird Biogeography II
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Atlas of the Ice Age Earth
Birds sing rainforest history
Geography and Ecology of Species Distributions
Geology: Plate Tectonics
Glaciers may not have driven modern bird evolution
and the Sea
to BIO 554/754 Syllabus