Avian flu impacts breeding of birds of prey
White-tailed eagles were most severely impacted in coastal areas.
The breeding success of many bird of prey species may have been impacted by avian flu, according to a report published by NatureScot.
The report identifies that eagles may have been particularly affected.
Analysis from the British Trust of Ornithology (BTO), using data from the Scottish Raptor Monitoring Scheme, has found that the proportion of golden eagles successfully breeding declined from 48 per cent in 2021 to 28 per cent. During the same period, breeding success for white-tailed eagle pairs dropped from 67 per cent to 45 per cent.
The research found that white-tailed eagles were most severely impacted in coastal areas, which has led to a possible link between infected seabirds and waterfowl that eagles may have preyed on or scavenged.
The largest declines recorded for both eagle species were in Lewis and Harris, where breeding success of golden eagles declined from 55 per cent to 16 per cent, and breeding success in white-tailed eagles dropped from 66 per cent to 24 per cent.
Avian flu was first detected in birds of prey in November 2021, then being identified in a range of species in April 2022. The impacts on breeding seem to be regional for some species, however they appear to be less localised for eagles.
While other factors can affect the breeding success of birds of prey, the 2022 data showed that complete nest failures with no surviving young were frequent. This is consistent with the effect of a highly contagious and pathogenic disease such as avian flu.
John Allan, NatureScot ornithology advisor, said: “Scotland still has strong eagle populations but these findings are very concerning. So far we have had fewer positive test results among birds of prey this year than last year, but it is early in the season and we can’t be complacent. We intend to repeat this analysis in 2023 to see if breeding success begins to improve.
“All partners in Scotland’s Avian Flu Task Force are continuing to work hard to understand this virus and take action to make our wild bird populations more resilient.”
With Strangles Awareness Week just around the corner (5-11 May), vets are being encouraged to share a survey about the disease with their horse-owning clients.
