Significant helminthiasis, ocular defects and other disorders in an endangered population of red-billed choughs (Pyrrhocorax pyrrhocorax): A descriptive observational study.

Abstract

Background: The breeding population of the red-billed chough (Pyrrhocorax pyrrhocorax) in Scotland has fallen in recent years, with all breeding pairs now confined to the Hebridean islands of Islay and Colonsay. Demographic studies have shown that a significant factor in the population decline on Islay has been reduced survival from fledging to 1 year of age (juveniles). Understanding the significance of infectious and non-infectious diseases in chough mortality is crucial to the development of successful management strategies aimed at conserving breeding populations of choughs in Scotland and elsewhere.

Methods: Postmortem examinations were carried out on 72 choughs found dead or euthanased on welfare grounds on Islay between 2004 and 2024.

Results: Significant burdens of helminths, some not previously recorded in choughs, were found in 18 juvenile choughs (78.3% of all juveniles examined). Genetic eye abnormalities analogous to Peters' anomaly in people were present in 16 nestling/fledgling choughs. Several other infectious and non-infectious causes of death were also found.

Limitations: The number of carcases examined was only a small sub-sample of all choughs dying on Islay.

Conclusion: Future strategies to conserve choughs on Islay will need to address the underlying causes of the increased losses from helminthiasis in juvenile choughs and assess the implications of inbreeding as demonstrated by the genetic eye disorders.