Microclimate and Host Body Condition Influence Mite Population Size in a Bird-Ectoparasite System

Parasite populations are not evenly distributed among the hosts they infect. Nest ectoparasites, such as mites, are no exception as their distribution is highly aggregated with considerable variability between and within sites. Here, I examine the influence of microclimate, nest characteristics, and host condition on ectoparasite population size in a bird-ectoparasite system. I experimentally infested Barn Swallow (Hirundo rusitca erythrogaster) nests with Northern Fowl Mites (Ornithonyssus sylvarium) and analyzed both biotic (nestling mass, wing length, and brood size) and abiotic (temperature, humidity, nest lining, nest dimensions, and substrate upon which the nest was built) predictors of mite population size. Temperature and humidity measurements were collected every ten minutes for 14 days using iButtons (Maxim Integrated), which are small data loggers that collect and store temperature and humidity measurements until retrieved from the field. My results suggest that mite populations are largest in nests that have hosts in good condition, with higher temperatures, lower humidity, and low prevalence of other arthropods. I also found that nests built on wood substrates support larger populations of mites than those constructed on metal or concrete. These findings lend insight into where one may expect to find higher prevalence of mites, when considering microclimate and host condition