What links all the birds that have gone extinct in the last 500 years?

Biologists have analysed the traits of all 216 bird species that have become extinct since 1500 in a bid to inform the conservation of endangered birds.

They found that species more likely to go extinct sooner were endemic to islands; unable to fly; had larger bodies; had sharply angled wings and were highly specialised in their ecological niches. The research is published in the journal Avian Research.

The study found more than 87% of the lost species were endemic to islands; nearly two-thirds inhabited forests; 45% ate primarily insects and other invertebrates; and 20% were completely or partially flightless.

Other research has looked at the traits of extinct birds. But this is the first study to correlate the species’ characteristics with the timing of extinctions.

“I’ve been very interested in extinctions and understanding the species that we’ve lost and trying to get a sense of how we can use the past to better inform the present and future,” says lead author Kyle Kittelberger, a graduate student at the University of Utah in the US.

About 2% of the world’s birds have gone extinct since 1500. But many species went extinct before then – the issue is that there isn’t a reliable record of the birds that went extinct, their traits and when they disappeared.

“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),” the authors write.

The decade of the 1890s saw the highest number of extinctions, with 21 recorded. The 1980s was another bad decade for bird loss with 20 species.

This latter decade “is noteworthy since focused and targeted conservation efforts were already underway globally before and during this period”, the authors say. “Though the rate of extinction declined in the subsequent decades, the number of globally threatened species has only increased.”

Across the board, the trait which most put bird species at risk was insularity – species endemic to islands.

Pacific islands have many endemic species. Hawai‘i has seen the highest loss of bird species with 34 disappearing since 1500 according to the study.

The bird family which saw the greatest number of extinctions is Rallidae, or rails. Since 1500, 26 of these medium-sized, semi-aquatic birds went extinct. The entire Mohoidae family – small nectar-sipping songbirds known as Hawai‘ian honeyeaters – have disappeared.

The team was surprised to find that birds with pointier wings vanished earlier. More pointed wings are associated with stronger flying and dispersal. It was predicted these traits might make the birds better equipped to respond to environmental pressures than those with rounder wings.

“It likely ties with the fact that a lot of these birds that went extinct were on islands,” Kittelberger says. “For these species or their ancestors to have arrived at these islands to begin with, they would’ve needed the ability to fly across large, open distances. So a lot of these birds on islands have, not necessarily longer, but more pointed wings.”

Today, 1,314 birds are on the IUCN Red List of Threatened Species – about 12% of total bird species.

Some, like the Akikiki (Oreomystis bairdi) endemic to Hawai‘ian island Kauai, are functionally extinct in the wild.