When Charles Darwin created modern biology with his theory of evolution he used the term “tree of life.”
For many years after, scientists speculated on how species were related and evolved by looking for similarities in looks and lifestyle.
Now, however, guessing is over since we can now read and follow changes in the DNA uniting living things. This supported some past speculation but there were big surprises.
Botany once included algae and mushrooms with higher plants, but we now know from DNA that mushrooms share a common ancestor with animals and are unrelated to plants while “algae” lumped plant related photosynthesizers with others unrelated including some bacteria. DNA even showed a surprising relation between hippos, dolphins, and whales.
Complete trees of life for large groups are now possible and we finally have one. A new book, “The Largest Avian Radiation” by Fjeldsa, Christidis, and Ericson provides just that for the 6,200 perching bird species, which are 60% of all birds.
Perching birds are tiny dinosaur descendants that survived the catastrophe that killed off their larger relatives, and their tree of life tells how that happened.
The big dinos were wiped out 66 million years ago when an asteroid hit what’s now Yucatan in the northern hemisphere.
Consequently, the southern hemisphere was where its devastation was least intense and where much more good habitat was present than exists there today because we know from fossils that large parts of Antarctica were forested then, rather than covered by ice.
No perching birds live there today but the most ancestral ones are in a suborder now confined to New Zealand, where the kind of southern hemisphere forests once present in Antarctica survive today.
Such forests are also present at the southern tip of South America, and that’s where evolution of the next most advanced perching bird suborder exploded into 1,350 species. Its two largest groups clearly evolved in South America, and while one of these extends only north to tropical Mexico, the other reaches Alaska and includes our flycatchers and kingbirds.
The suborder’s third and smaller group is most diverse in southeast Asia, but its most ancestral species is confined to South America’s wettest rainforest, and some intermediate species in Africa suggest this group may have reached Asia through there by crossing a then narrower south Atlantic.
That suborder is known as the suboscines because it lacks anatomy for producing complex songs. All other perching birds are in a more advanced suborder called oscines or songbirds, and its most ancestral members are 322 species found in and near Australia, which can proudly call itself the “continent where song began.” Families of these basal oscines likely most familiar to non-Australians are lyrebirds, bowerbirds, and honeyeaters.
New Guinea, a land mass north of Australia created when that continent collided with volcanic islands as it drifted north from Antarctica, gave rise to the first group of songbirds that invaded the rest of the world.
It consisted of around 800 species and even included three families that reached the Americas: shrikes, vireos, and the crow and jay family, which includes ravens, the biggest perching birds. One family in this group remained in New Guinea, however, the spectacular birds of paradise.
By far the largest group of perching birds are the 3,900 species of higher oscines that also spread from New Guinea to first the Old World and then the Americas. Older groups among them are less diverse and widely scattered around the world but some are familiar here: kinglets, waxwings, and phainopeplas.
More recent higher oscines are in several superfamilies, the smallest of which has just 2 families. The larger of these consists of tits and chickadees, and the smaller has only one American species, the verdin of our deserts.
A much larger superfamily, the Old World warblers, has few families that reach the Americas but exceptions are larks, swallows, bushtits, and wrentits.
A smaller superfamily better developed in the Americas includes nuthatches, tree creepers, gnatcatchers, and wrens, but another large one, Old World warblers, includes starlings and 3 families that naturally reach the Americas: dippers, mockingbirds/thrashers, and thrushes.
The last of these superfamilies is the largest, with 1,500 species. It began in the Old World but achieved some of its greatest diversity in the Americas.
An innovation helping it reach this success was a conical bill enabling grass seeds to be cracked and eaten acquired 10 million years ago just when climate change caused grass to replace many forests. Its early members lacking this bill were all Old World except the olive warbler, a one species family living from Arizona to Nicaragua.
Early conical bill families began in the Old World and included our familiar introduced house sparrow, but two of them extended naturally to the Americas: pipits and finches.
Seven groups of the latter provide our finches, crossbills, and many of our grosbeaks and another that reached Hawaii provides its diverse honeycreepers.
That superfamily has an advanced group of 16 families that includes 5 families providing much of our perching bird diversity: 142 species are our American sparrows; 111 are our wood warblers, which switched back to insects from grass; 108 are our blackbirds, orioles, and meadowlarks; 52 are our cardinals; and, largest of all, 327 are our tanagers.
Reading DNA finally sorted out this complex pattern and provided some surprises: yellow-breasted chats are with orioles, not wood warblers, and our tanagers, like the western, are actually cardinals.
The huge tanager diversity is mostly in South America, and a surprise inclusion are the Galapagos finches made famous by Darwin. The only true tanager reaching the United States and just barely is the white-collared seedeater.
In addition to 10 chapters constructing the perching bird tree of life in detail, the book has range maps of their many families, beautiful accurately colored paintings of many, and ten other chapters and two appendices on subjects explaining these birds’ evolution and often useful for other species.
The first appendix, for example, summarizes ecological information quite relevant to California as well as the rest of the world.
This is by far the best and most useful one volume biology book I’ve ever come across.
Dr. Holstein is a retired consulting ecologist who worked in much of California, a long-time conservation activist with the California Native Plant Society, and a board member of Tuleyome, a Woodland, California-based nonprofit conservation organization.
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September 11, 2021 at 06:03PM
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