No effects of a feather mite on life-history components and grooming behaviour in the Seychelles warbler, Acrocephalus sechellensis

A common assumption of studies examining host-symbiont interactions is that all symbiotic organisms are parasitic. Feather mites are widespread symbionts of birds that do not appear to deplete the host of any vital resources. Instead they feed on the oily secretions that cover the feathers and the detritus caught in these secretions. Therefore, a more logical assumption might be that feather mites are non-parasitic. We investigated whether infestation by a feather mite, Trouessartia sp. (Trouessartiidae), has any detrimental effects on the Seychelles warbler, Acrocephalus sechellensis. Feather mite load was not correlated with body condition. Survivorship of birds per territory was lower for birds with lower mite loads, but this result is explained by these birds also living in low-quality territories with low food availability. The amount of time birds spent grooming was not related to feather mite load and grooming did not decrease following the experimental removal of mites. Additionally, although males groom more than females, they do not have larger mite loads than females. Although this study is largely non-experimental, the combined results indicate that the relationship between these feather mites and the Seychelles warbler is probably benign.