Le highly pathogenic avian influenza (HPAI) virus in 2022 led to a high mortality rate among gannets of the Rouzic colony (France), with a decline of 38 % of the breeding population. Among the survivors, 22,3 % had blackened eyes (figure c above), a sign of previous infection.
This article from Aurore Ponchon and colleagues, published in Biological Conservation, shows that these individuals do not show any notable differences in their foraging behaviour. On the other hand, the reduction in the number of birds is accompanied by a reduced foraging effort and increased reproductive success, in line with the Ashmole halo hypothesis: when colonies are less dense, competition for food around the breeding site decreases, allowing the birds to feed closer and more efficiently.
These results underline the importance of density-dependent mechanisms after mass mortalities, while warning of the long-term risks for populations that are already weakened.