Knemidokoptic mite infestation of island populations of Red-winged Blackbirds (Agelaius phoeniceus)

Knemidokoptic mites infest many bird species around the world and may lead to decreased survival, although relatively few studies have documented long-term effects on populations. We present 9 years of data monitoring the survival of Red-winged Blackbirds (Agelaius phoeniceus) in islands of Lake Erie, Ohio, USA. Blackbirds in our study first appeared with mite infestation in 2012. Percentage of the total number of blackbirds infested with mites peaked at 7.3% in 2013 and persisted at 5-6% through the summer of 2018. We saw no differences in infestation rates based on blackbird sex or age. Unlike most other studies, in subsequent years we did recapture birds that had previously had infestations, and we detected no decline in recapture rate due to mite infestation. While that does not mean that blackbirds do not experience negative consequences of infestation, our evidence does suggest that low-level infestation may be persistent in a population without dramatic declines in survivorship.