Biologists at the University of Utah conducted an analysis to identify traits that correlate with the 216 bird extinctions since 1500. The goal was to inform conservation efforts for critically endangered species.
The study found that birds most likely to go extinct sooner tended to have certain characteristics: they were often endemic to islands, lacked the ability to fly, had larger bodies and sharply angled wings, and occupied ecologically specific niches.
While some of these findings align with previous research, this study is the first to directly correlate these traits with the timing of extinctions.
Lead author Kyle Kittelberger, a graduate student at the School of Biological Sciences, emphasized the importance of understanding past extinctions to better guide present and future conservation efforts.
Kyle Kittelberger and his team used BirdBase, a comprehensive dataset of ecological traits for over 11,600 bird species compiled by University of Utah professor Çağan Şekercioğlu, to analyze the characteristics associated with bird extinctions. Their research examined a wide range of biogeographical, ecological, and life history traits linked to extinction risk for species that have gone extinct and those that are no longer confirmed in recent sightings.
A key aspect of the study was its focus on when birds went extinct. This provided a novel perspective on extinction timing that helps explain why certain bird species with specific traits disappeared at particular times.
Kittelberger emphasized that one of the study’s strengths was its simultaneous analysis of multiple traits, in contrast to previous research that often looked at traits in isolation. The team’s findings can guide conservation efforts for many at-risk bird species by identifying the traits most strongly linked to extinction.
While only around 2% of the world’s bird species have gone extinct since 1500, the year Kittelberger’s analysis begins, even more had already disappeared. Before 1500, however, a record of the extinct birds and data on their traits and characteristics is less reliable.
The timing of bird extinctions aligns with the rise of scientific observation and systematic documentation of plant and animal life, which coincided with the expansion of European exploration. This period saw significant disruptions to ecosystems globally due to colonization and the introduction of non-native species.
Currently, 1,314 bird species are at risk of extinction, according to the IUCN Red List of Threatened Species, representing about 12% of all bird species. Some species, like the ‘Akikiki (Oreomystis bairdi), endemic to the Hawaiian island of Kauai, are so rare that they are functionally extinct. Kittelberger photographed the ‘Akikiki in 2022 in the Alaka’i Wilderness Preserve, where it was believed that around 70 individuals remained in the wild. Tragically, today, only one individual of this species is still alive.
As reported by Hawaii’s Division of Forestry and Wildlife, introduced species, such as malaria-carrying mosquitoes and habitat-damaging livestock, are the primary threats to survival for many Hawaiian bird species.
One of the most critical factors associated with extinction risk is ‘insularity’ —species endemic to islands are particularly vulnerable. Traits like large body size, specialized wing shapes, and ecological specialization, which also increase extinction risk, are often linked to island-dwelling species.
Pacific islands, known for their high levels of endemic species, have suffered severe biodiversity loss, with Hawaii being the most affected. The Hawaiian archipelago has experienced the greatest avian biodiversity loss, accounting for 34 bird extinctions since 1500.
The bird family Rallidae (rails) experienced the most extinction, losing 26 species. In contrast, the Mohoidae family, consisting of Hawaiian honeyeaters, is completely extinct, with its last member, the Kauai O’o, disappearing in 1987. A surprising discovery by Kittelberger’s team was the link between wing shape and extinction.
Birds with more pointed wings, indicating stronger flight and dispersal abilities, were found to be more likely to have gone extinct earlier, contrary to expectations that these birds would be better able to adapt to environmental changes.
Birds with rounder wings and smaller hand-wing ratios were found to be more resilient to extinction, likely because they were better adapted to their environments. Kittelberger explained that many extinct birds were island species that needed pointed wings for long-distance flight, similar to swifts, swallows, and albatrosses.
These birds could travel vast open distances, whereas birds in dense habitats like rainforests have rounder wings suited for shorter, local movements. Ecological specialists, who are more adapted to specific niches, struggle when these niches are disrupted by factors like invasive species or food source loss, making them less adaptable to environmental changes.
The study found that over 87% of the extinct bird species were endemic to islands, with nearly two-thirds living in forests. About 45% of these species primarily feed on insects and other invertebrates, while 20% are either fully or partially flightless. Additionally, larger-bodied species were disproportionately represented on the extinction list, suggesting that bigger birds were more vulnerable to extinction.
Scientists noted, “Heavier birds have been more likely to be targeted for hunting, with several well-known examples of birds being hunted to extinction in part for food, including the Dodo, Great Auk (Pinguinus impennis), and Spectacled Cormorant (Urile perspicillatus).”
“Body mass has also been linked with a species’ inhabitance of islands, as island birds tend to be larger than mainland species. Of the 43 species whose average body weight exceeded 500 grams, or 1.1 pounds, three-quarters were endemic to an island.”
The 1890s saw the highest number of bird extinctions, with 21 species lost. The 1980s also marked a significant period of bird loss, with 20 species, including the Kauai O’o, going extinct. Despite ongoing global conservation efforts during this time, the study noted that while the extinction rate has declined in recent decades, the number of globally threatened bird species has continued to rise.
Journal Reference:
- Colby J. Tanner, Amy N. Buxton, Amira Prewett and Çağan Şekercioğlu. Correlates of avian extinction timing around the world since 1500 CE. Avian Research. DOI: 10.1016/j.avrs.2024.100213