Abstract
Feather mites are obligatory ectosymbionts of birds that primarily feed on the oily secretions from the uropygial gland. Feather mite abundance varies within and among host species and has various effects on host condition and fitness, but there is little consensus on factors that drive variation of this symbiotic system. We tested hypotheses regarding how within‐species and among‐species traits explain variation in both (1) mite abundance and (2) relationships between mite abundance and host body condition and components of host fitness (reproductive performance and apparent annual survival). We focused on two closely related (Parulidae), but ecologically distinct, species: Setophaga cerulea (Cerulean Warbler), a canopy dwelling open‐cup nester, and Protonotaria citrea (Prothonotary Warbler), an understory dwelling, cavity nester. We predicted that feather mites would be more abundant on and have a more parasitic relationship with P. citrea, and within P. citrea, females and older individuals would harbor greater mite abundances. We captured, took body measurements, quantified feather mite abundance on individuals’ primaries and rectrices, and monitored individuals and their nests to estimate fitness. Feather mite abundance differed by species, but in the opposite direction of our prediction. There was no relationship between mite abundance and any measure of body condition or fitness for either species or sex (also contrary to our predictions). Our results suggest that species biology and ecological context may influence mite abundance on hosts. However, this pattern does not extend to differential effects of mites on measures of host body condition or fitness.
Highlights
Many organisms engage in intimate relationships with other species, and these symbiotic relationships are commonly categorized as parasitic, commensal, or mutualistic
Feather mites are obligatory ectosymbiotic arthropods that inhabit the small spaces between feather barbs and are thought to primarily feed on oily secretions from the uropygial gland, which are distributed across feathers by preening (Proctor, 2003)
Generalized linear models (GLMs) were built for each species and sex to evaluate the relationship between feather mite abundance and apparent annual survival status, and the potentially confounding variables of geolocator status and age were included as fixed effects in models
Summary
Many organisms engage in intimate relationships (symbioses) with other species, and these symbiotic relationships are commonly categorized as parasitic, commensal, or mutualistic. We predicted that relationships between mite abundance and (a) body condition and (b) host fitness will be more strongly negative (i.e., mites will have a more parasitic effect) for understory dwelling, cavity-nesting species than for canopy dwelling, open-cup nesters, and even more so for female cavity nesters than for conspecific males. We evaluated both reproduction and annual survival of individuals and we quantified feather mite abundance using a novel, objective system that included all primary and rectrix feathers
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