Birds groom more in regions with higher parasite pressure: a comparison of temperate and subtropical American kestrels

Grooming behaviour, which maintains and cleans the integument, is a widespread behaviour of birds, mammals and arthropods. The extent to which grooming is influenced by large-scale environmental differences, such as geographical and seasonal variation, remains largely unexplored. We investigated spatial and temporal variation in the grooming behaviour of a common species of bird, the American kestrel, Falco sparverius. Specifically, we compared the self-grooming behaviour (preening and scratch-ing) of kestrels in the subtropical Bahamas to kestrels in temperate northern Utah, U.S.A., in both summer and winter. We also compared differences in parasite 'pressure' by quantifying the prevalence and abundance of ectoparasitic lice (Insecta: Phthiraptera) on kestrels in both locations. Bahama kestrels had significantly more lice than Utah kestrels, which is typical of birds in humid regions, compared to arid regions. Bahama kestrels groomed significantly more than Utah kestrels, which may constrain the time-activity budgets of Bahama kestrels. Within each region, however, birds with more lice did not groom more. This pattern is consistent with geographical differences in programmed grooming, rather than stimulus-driven grooming. Kestrels in both locations groomed significantly more in summer than in winter, presumably because feather moult occurs in summer. To our knowledge, this study provides the first demonstration of geographical variation in the grooming behaviour of any animal. Experimental studies are needed to confirm the causes and consequences of this variation. Spatial and temporal comparisons of grooming in other birds, as well as mammals and arthropods, would be informative.& COPY; 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.