Understanding the factors influencing mortality from HPAI in UK seabird colonies: integrating mortality data and an individual-based modelling approach.

In the UK, outbreaks of highly pathogenic avian influenza (HPAI) resulted in wide-scale mortality in colonies of breeding seabirds in 2022 and 2023, however the severity of impacts varied substantially between species and sites. Understanding why some colonies were affected more severely than others has the potential to inform future management actions to mitigate impacts. To address this question, 40 colonies identified as being high priority sites were monitored within the UK across the 2022 and 2023 breeding seasons, with counts of carcasses collated as well as site-specific data on the colony and any management approaches to HPAI taken. We fitted generalised linear models to test for factors influencing whether colonies were impacted by HPAI and the extent of mortality in ground-nesting tern and small gull species. In addition, data from these sites, together with information from the literature, was used to calibrate an individual-based simulation model for the spread of HPAI through a ground-nesting seabird colony, parameterised to represent Sandwich Tern and Black-headed Gull colonies. We use this model to further explore the potential effectiveness of carcass removal as a mitigation measure to reduce the resulting mortality within colonies.

Dr Susannah Gold, RSPB Dr Viv Booth, RSPB Nik Ward, Natural England Rebecca Jones, Natural England Bart Donato, Natural England

Mortality estimations, impacts on harvest, conservation considerations, and potential mitigation strategies in wild birds