Epidemiology of protozoan and helminthic parasites in wild passerine birds of Britain and Ireland

Avian endoparasites play important roles in conservation, biodiversity, and host evolution. Currently, little is known about the epidemiology of intestinal helminths and protozoans infecting wild birds of Britain and Ireland. This study aimed to determine the rates of parasite prevalence, abundance, and infection intensity in wild passerines. Faecal samples (n = 755) from 18 bird families were collected from thirteen sites across England, Wales, and Ireland from March 2020 – June 2021. A conventional sodium nitrate flotation method allowed morphological identification and abundance estimation of eggs/oocysts. Associations with host family and age were examined alongside spatiotemporal and ecological factors using Bayesian phylogenetically-controlled models. Parasites were detected in 20.0% of samples, with corvids and finches having the highest prevalences and intensities respectively. Syngamus (33%) and Isospora (32%) were the most prevalent genera observed. Parasite prevalence and abundance differed amongst avian families and seasons, while infection intensity varied between families and regions. Prevalence was affected by diet diversity, while abundance differed by host age and habitat diversity. Infection intensity was higher in birds using a wider range of habitats, and doubled in areas with feeders present. The elucidation of these patterns will increase the understanding of parasite fauna in British and Irish birds.