The birds with the most unique characteristics, including wing length and beak shape, are also the most endangered, according to researchers at Imperial College London who analysed the extinction risks and physical attributes of almost all living bird species in the most comprehensive study of its kind.

The scientists examined a dataset of various measurements from beak to tail collected from living birds and museum specimens belonging to nearlt 10,000 avian species. They combined these morphological data with extinction risks based on each species’ threat status on the IUCN Red List.

The scientists also ran computer simulations to see what would happen if the most threatened birds went extinct. In these simulated scenarios there was a much greater reduction in the morphological diversity among birds than in scenarios where extinction stayed random.

The results showed that morphologically unique birds facing the threat of extinction in the wild include the Christmas Frigatebird (Fregata andrewsi), which nests only on Christmas Island, and the Bristle-thighed Curlew (Numenius tahitiensis), which migrates annually from Alaska to South Pacific islands.

“Our study shows that extinctions will most likely prune a large proportion of unique species from the avian tree. Losing these unique species will mean a loss of the specialised roles that they play in ecosystems,” such as seed dispersal, pollination and predation, according to Jarome Ali, a PhD candidate at Princeton University who completed the research at Imperial College London and was the lead author of the study.

“If we do not take action to protect threatened species and avert extinctions, the functioning of ecosystems will be dramatically disrupted,” the scientist warns.

The reason for why birds with more unique traits are facing increased hardships has several reasons, the scientists say.

“One possibility is that highly specialised organisms are less able to adapt to a changing environment, in which case human impacts may directly threaten species with the most unusual ecological roles. More research is needed to delve deeper into the connection between unique traits and extinction risk,” Ali says.