Birds are in danger of extinction

Birds that forage underwater — like penguins, loons and grebes — may be more likely to become extinct than their non-diving cousins, a new study finds.

Many waterfowl have developed very specific bodies and behaviors to facilitate this. Now, an analysis of the evolutionary history of more than 700 species of waterfowl shows that once a bird group acquires the ability to concentrate, the change is irreversible. That inflexibility may help explain why breeding birds have an elevated extinction rate compared to non-breeding birds, researchers report on Dec. 21. Proceedings of the Royal Society B..

“The morphological adaptations are substantial,” says Catherine Sheard, an evolutionary biologist at the University of Bristol in England, who was not involved in the study. Like birds that dive from the air into the water, such as gannets and some pelicans, they can have tweaks up to the muscles of the neck, and the bones in the chest.

It is possible that some bird taxa evolve under evolutionary scale, where adaptations to use a particular food source or habitat open up new opportunities, but also encourage more and more specialized evolutionary tailoring. These birds can be caught in their tracks, increasing the risk of extinction. That is especially true if their habitat is rapidly changing in some negative way, perhaps due to human-induced climate change.SN: 1/16/20).

Evolutionary biologists Josh Tyler and Jane Young studied the evolution of tribes in the Aequorlitornithe, a collection of 727 species of waterfowl across 11 bird groups. The team divided the species into birds that were either non-dive, or one of three types of taxa: foot-followers (such as loons and grebes), wing-followers (such as penguins and auks) and various divers.

Dividing has evolved at least 14 separate times in waterfowl, but there have been no instances where dividing birds have reverted to a nondividing form, the researchers found.

Scientists have also explored the connection between taxa and the evolution of new species, or the extinction of different generations of birds. Among the 236 taxonomic bird species, 75, or 32 percent, were part of the lineages that suffer 0.02 per million years more extinctions than the generation of new species. This elevated extinction was more frequent in oars and foot chases compared to divers divers. A bird that does not breed offspring, on the other hand, has generated 0.1 more new species per million years than there are species of dying species.

“The more specific you become, the more you are in a certain diet, feeding plan or environment,” says Tyler, of the University of Bath in England. “The field environment for foraging resources is much greater for non-commercial birds than for specialist divers, and this can play into their ability to adapt and thrive.”

Inside the group of birds, the less specific, the better. Take Aptenodytes, a group that has become the subject of a fair share of conservation concern (SN: 8/1/18). Researchers point out that penguins are gentoo (Pygoscelis papua) — which have a broad diet — have larger population sizes than the related chinstrap penguins (P. antarcticus) that eat mostly krill, and there are actually as many as four recently diverging species.

The International Union for Conservation of Nature considers both penguin species to be of “least concern” in terms of imminent danger of extinction. However, chinstrap numbers are declining in some areas, while large populations remain generally stable.

If some birds are trapped in their adaptations to their environment, that doesn’t bode well for long-term survival, say Tyler and Junior, who is at the University of Tasmania in Hobart.

According to the IUCN, 156 species, or about a fifth, of the 727 waterbird species are considered vulnerable, endangered or critically endangered. Researchers calculate that 75 species of birds are taxed by increased extinction rates, 24 species or nearly a third of those already listed as threatened.