Birds that dive underwater — such as penguins, loons and grebes — may be more likely to go extinct than their nondiving kin, a new study finds.
Many water birds have evolved highly specialized bodies and behaviors that facilitate diving. Now, an analysis of the evolutionary history of more than 700 water bird species shows that once a bird group gains the ability to dive, the change is irreversible. That inflexibility could help explain why diving birds have an elevated extinction rate compared with nondiving birds, researchers report in the Dec. 21 Proceedings of the Royal Society B.
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“There are substantial morphological adaptations for diving,” says Catherine Sheard, an evolutionary biologist at the University of Bristol in England, who was not involved with the study. For instance, birds that plunge into the water from the air, such as gannets and some pelicans, may have tweaks to the neck muscles and the bones in the chest.
It’s possible that some diving birds are evolving under an evolutionary “ratchet,” where adaptations to exploit a certain food source or habitat unlock some new opportunities, but also encourage ever more specialized evolutionary tailoring. These birds may become trapped in their ways, increasing their risk of extinction. That’s especially true if their habitat rapidly changes in some negative way, possibly because of human-caused climate change (SN: 1/16/20).
Evolutionary biologists Josh Tyler and Jane Younger investigated the evolution of diving in Aequorlitornithes, a collection of 727 water bird species across 11 bird groups. The team divided species into either nondiving birds, or one of three diving types: foot-propelled pursuit (such as loons and…
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