Analysis of 216 extinct bird species conducted by biologists indicated that those species endemic to islands, that occupied specific ecological roles, were often large-bodied, had sharply angled wings, and could not fly were among the most vulnerable to extinction after the year 1500.
To aid in the preservation of critically endangered bird species, researchers at the University of Utah carried out a study to identify characteristics linked to the extinction of all 216 bird species observed since 1500.
The species most at risk of early extinction were found predominantly on islands, unable to fly, had larger physical appearances, and exhibited sharply angled wings, all while occupying specific ecological niches, as noted in recent research.
While some of these results align with earlier studies on extinct birds, this analysis is unique in connecting bird characteristics directly with the timing of their extinctions, according to lead author Kyle Kittelberger, a graduate student from the School of Biological Sciences.
“I am deeply interested in extinctions, wanting to comprehend the species that we have lost and how we can learn from past extinctions to influence our present and future actions,” stated Kittelberger, who is also focusing his dissertation on the adaptations of migratory songbirds in relation to climate change impacts.
The research team utilized BirdBase, a comprehensive database of ecological traits belonging to over 11,600 bird species, created by U biology professor Ça?an ?ekercio?lu along with the Biodiversity and Conservation Ecology Lab at the U. They performed a simultaneous analysis of a wide variety of biogeographical, ecological, and life history traits previously associated with extinction risks in bird species, whether they were confirmed extinct or considered lost due to lack of sightings.
“Crucially, we explore the biological factors linked to bird extinctions with a focus on the timing of these events, which provides a fresh perspective to understand why birds with certain characteristics went extinct at specific times,” Kittelberger communicated via a series of X posts. By pinpointing traits that predispose certain birds to extinction, their findings aim to better inform conservation strategies for numerous threatened species.
“A key advantage of our methodology is that we assessed all these traits in relation to one another, unlike many previous research studies that examined traits in isolation.”
Since 1500, only about 2% of the world’s bird species have faced extinction as confirmed by Kittelberger’s analysis, but a greater number had already been lost by that time. There is not a reliable record of the birds that vanished before 1500, nor adequate data about their traits and characteristics.
This period correlates with the advancement of scientific observation that began systematically documenting flora and fauna. It was also when European exploration surged, disrupting ecosystems worldwide due to colonization and the introduction of new species.
Currently, 1,314 bird species are classified as at risk of extinction according to the IUCN Red List of Threatened Species, making up about 12% of all bird species.
Many species, like the ‘Akikiki (Oreomystis bairdi), native to Kauai in Hawaii, have dwindled to such numbers that they are functionally extinct. Kittelberger captured an image of the ‘Akikiki, also referred to as Kauai’s creeper, in the Alaka’i Wilderness Preserve in 2022 when it was estimated that only around 70 individuals remained in the wild; today, that number has dropped to just one.
The study highlighted that a significant portion of the 216 bird species that went extinct or are thought to be lost since 1500 were endemic, mainly found on islands, and either flightless or partially flightless. It also detailed species distribution by their primary habitat or dietary preferences.
For the ‘Akikiki, the principal threat arises from introduced species, especially mosquitoes that carry diseases and livestock that destroy habitats, as noted by Hawaii’s Division of Forestry and Wildlife.
Insularity, or being endemic to islands, emerged as the most critical factor linked to extinction risk. Other risk-enhancing traits, such as size, wing shape, and ecological specialization, are also tied to this insularity.
Pacific islands host a variety of endemic species, many now listed by the IUCN. Hawaii stands out as an archipelago with the most significant decline in avian biodiversity, suffering 34 extinctions since 1500, as noted in the study.
The family of birds that faced the most extinctions is Rallidae, known as rails, which are medium-sized, semi-aquatic birds distributed worldwide. This family has lost 26 species, while the entire Mohoidae family, small nectar-feeding birds known as Hawaiian honeyeaters, has become entirely extinct (the only bird family to completely vanish in modern history). The last member of this family, the Kauai O’o (Moho braccatus), was last spotted in 1987.
One surprising discovery from Kittelberger’s team was the link between wing shape and extinction risk. They observed that bird species with more pronounced wing shapes (higher hand-wing index) tended to disappear earlier. Since pointier wings suggest superior flight and dispersal capabilities, it was expected that these birds would adapt better to environmental changes than their rounder-winged counterparts.
Conversely, birds with rounder wings, indicating smaller hand-wing ratios, appeared to demonstrate greater resilience.
“This is likely related to the fact that many of the birds that went extinct were island dwellers. For these species or their ancestors to have arrived on these islands, they would have needed the ability to fly long distances. Thus, many island birds possess pointy wings, not necessarily longer but more streamlined,” Kittelberger explained. “Consider birds like swifts, swallows, or albatrosses that traverse oceans. Their pointed wings facilitate efficient flight, while birds inhabiting dense tropical forests have rounded wings due to their movement being restricted to their local environment.”
Ecological specialists, who thrive in specific niches, find it exceedingly difficult to adapt when those niches are altered, making them less capable of coping with disturbances like invasive species or the disruption of their food sources.
Further findings revealed that over 87% of the studied species were island endemics; nearly two-thirds lived in forests; 45% primarily consumed insects and other invertebrates, and 20% were entirely or partially incapable of flight. Additionally, larger-bodied species were disproportionately represented among the extinct list.
“Larger birds are often more vulnerable to hunting, with several well-known instances where birds were driven to extinction partly due to hunting for food, including the Dodo, Great Auk (Pinguinus impennis), and Spectacled Cormorant (Urile perspicillatus),” the study indicated. “Larger body mass has also been associated with species’ occurrences on islands, as island birds generally tend to be larger than those on the mainland.” Of the 43 species weighing over 500 grams or 1.1 pounds on average, around 75% were found exclusively on islands.
The 1890s recorded the highest number of avian extinctions, with 21 documented. The 1980s also witnessed significant losses, with 20 species disappearing, including the Kauai O’o. This decade stands out as conservation efforts had already begun increasing globally both prior to and during this time,” the study reported. “While the rate of extinction has slowed in subsequent decades, the number of globally threatened species continues to rise.”
The study titled “Correlates of avian extinction timing around the world since 1500 CE” was published on November 7 in the journal Avian Research. The research team comprised Colby J. Tanner, Amy N. Buxton, Amira Prewett, and Ça?an ?ekercio?lu. The University of Utah’s Graduate Research Fellowship provided support for this research.
