To assist in the conservation of endangered bird species, biologists from the University of Utah have conducted an analysis that pinpoints characteristics linked to all 216 bird extinctions since the year 1500.
The species that are most likely to go extinct quickly were found to be those that are endemic to islands, incapable of flight, have larger bodies and sharply angled wings, while also occupying very specific ecological roles, as revealed in research published this month.
Although some of these observations align with earlier studies concerning extinct birds, this is the first study that connects bird traits to the timing of their extinctions, according to lead author Kyle Kittelberger, a graduate student in the School of Biological Sciences.
“My interest lies in understanding extinctions and the species we’ve lost, as well as how we can leverage historical data to better inform current and future conservation efforts,” stated Kittelberger, who is working on his dissertation regarding how migratory songbirds’ bodies and wings have evolved due to climate change.
The analysis utilized BirdBase, a comprehensive dataset of ecological traits for over 11,600 bird species, assembled by University biology professor Ça?an ?ekercio?lu along with the Biodiversity and Conservation Ecology Lab at the University. The research team simultaneously examined a wide range of biogeographical, ecological, and life history traits previously associated with extinction risk for both species that have become extinct and those that lack recent confirmed sightings and are considered functionally extinct.
“Importantly, we analyze biological factors related to bird extinctions by examining when the extinctions occurred, adding a unique timing aspect that helps clarify why birds with specific characteristics disappeared when they did,” Kittelberger shared in a series of posts on X. By pinpointing the traits that predispose birds to extinction, the findings aim to aid conservation initiatives for hundreds of species that face threats.
“One of the advantages of our methodology is the simultaneous comparison of all these traits, whereas many previous studies have focused on traits in isolation.”
Since 1500, approximately 2% of the world’s bird species have disappeared, which marks the starting point of Kittelberger’s analysis. However, even more species had vanished prior to that date. The extinction records before 1500 are less reliable, and there is limited data on the traits and characteristics of those species.
This timing aligns with the advent of scientific observation, leading to the systematic recording of plant and animal species. It also coincides with the surge of European exploration, resulting in ecological disturbances around the world due to colonization and the introduction of invasive species.
Currently, 1,314 bird species are at risk of extinction, representing about 12% of the total bird population, according to the IUCN Red List of Threatened Species.
Many of these species, such as the ‘Akikiki (Oreomystis bairdi), native to the Hawaiian island of Kauai, are so rare that they are functionally extinct. Kittelberger photographed an ‘Akikiki, also known as Kauai’s creeper, in the Alaka’i Wilderness Preserve in 2022, when it was estimated that around 70 individuals remained in the wild; today, there is only one known individual left.
This research outlines the percentage of the 216 bird species that have become extinct or are likely lost since 1500, specifically highlighting those that are endemic to certain regions and exist solely on islands, either being flightless or partially capable of flight, as well as analyzing the categories of species based on their primary habitats or diets.
As with many other Hawaiian bird species, the greatest threat to the ‘Akikiki is posed by introduced species, particularly mosquitoes that carry malaria and livestock that damage their habitats, as reported by Hawaii’s Division of Forestry and Wildlife.
The crucial factor most associated with extinction is being endemic to islands. Additional traits that appear to enhance extinction risk include body size, wing shape, and ecological specialization—traits that are also linked with island endemism.
The Pacific islands harbor a diverse array of endemic species, many of which are listed by the IUCN. Hawaii has suffered the greatest loss of avian biodiversity, with 34 extinctions recorded post-1500, as noted in this study.
The bird family that faced the highest number of extinctions is Rallidae, or rails, which are medium-sized, semi-aquatic birds found globally. This family has lost 26 members, while the Mohoidae family, small nectar-feeding songbirds known as Hawaiian honeyeaters, has completely vanished (this is the only bird family to have gone extinct in modern times). The last known member of this family, the Kauai O’o (Moho braccatus), was last seen in 1987.
A surprising finding from Kittelberger’s team was the link between wing shape and extinction risk. They discovered that bird species with a greater hand-wing index (more pointed wings) were more likely to have become extinct sooner. Since pointed wings are indicative of better flight capabilities, the researchers initially assumed these birds would be more adaptable to environmental challenges compared to those with rounder wings.
However, the analysis revealed that birds with rounder wings and smaller hand-wing ratios displayed greater resilience.
“This is probably tied to the fact that many of the extinct species were island dwellers. Those species or their ancestors needed strong flying abilities to reach these islands in the first place, leading to longer, more pointed wings,” Kittelberger explained. “Consider species like swifts, swallows, or albatrosses, which possess pointed wings suited for long-distance flight, in contrast to birds in dense tropical rainforests that move around their local habitat, leading them to have rounder wings.”
Ecological specialists—those that thrive in specific ecological niches—struggle to adapt when their environments change, making them more vulnerable to threats like invasive species or food source disruptions.
In other findings, the study revealed that over 87% of the extinct or likely extinct species were island endemics; nearly two-thirds lived in forested habitats; 45% primarily fed on insects and other invertebrates; and 20% were completely or partially flightless. Additionally, larger-bodied species were disproportionately represented in the list of extinct birds.
“Larger birds are often more susceptible to hunting, evidenced by notable examples like the Dodo, Great Auk (Pinguinus impennis), and Spectacled Cormorant (Urile perspicillatus), which faced extinction partly due to hunting for food,” the study observed. “Body mass is also correlated with island residency, as birds on islands tend to be larger than those on the mainland.” Of the 43 species with an average body weight over 500 grams (1.1 pounds), three-quarters were island endemics.
The decade of the 1890s recorded the highest number of extinctions, totaling 21. The 1980s was another challenging decade, with 20 species lost, including the Kauai O’o. This decade is notable as various targeted conservation efforts were already underway globally. Although subsequent decades saw a decline in extinction rates, the number of threatened species has only increased.
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 included Colby J. Tanner, Amy N. Buxton, Amira Prewett, and Ça?an ?ekercio?lu. The study received support from the University of Utah’s Graduate Research Fellowship.
