Avoidance, tolerance, and resistance to ectoparasites in nestling and adult tree swallows

Abstract

We examined avoidance, tolerance, and resistance strategies of nestling and adult tree swallows Tachycineta bicolor in response to ectoparasitic blowflies Protocalliphora sialia. Tree swallows avoided settling in north-facing nest boxes early in the breeding season. These boxes were more likely to be parasitized later in the season, suggesting that box selection may facilitate blowfly avoidance. After experimentally manipulating blowfly intensity, we found that nestlings were generally tolerant of parasitism. Parasites significantly reduced nestling blood hemoglobin but had no effect on nestling body mass, primary feather growth, age at fledging, or fledging success. Parents of parasitized nestlings did not increase their food provisioning rate to promote nestling tolerance. Adult female tree swallows demonstrated both tolerance and resistance: blowfly parasitism had no effect on adult hemoglobin and body mass, and those with higher P. sialia-binding antibody levels had fewer blowfly larvae in their nests. Nestling antibodies were unrelated to blowfly intensity. Despite considerable variation among years, our results suggest that the costs of blowfly parasitism to nestling and adult tree swallows are modest, and limited to blood loss in nestlings. Future work should examine the effects of reduced blood hemoglobin on fledgling survival and the importance of parasite-specific antibodies.

Host tolerance and resistance to parasitic nest flies differs between two wild bird species

“…Once eggs appeared, nests were checked every other day until nestlings hatched. At hatching, the nestlings and top liner of the nest cup (i.e., just enough material to provide a barrier between the insecticide and nestlings) were removed in order to treat the nest with either water (parasitized treatment) to allow for natural parasitism or a 1% permethrin solution to remove all parasites (nonparasitized treatment) (DeSimone et al, ; Knutie et al, ). The treatment for each species was initially determined by a coin flip, and the following nests were assigned by alternating treatment for each nest.…”

“…One potential model system to study how host defense mechanisms differ between species in response to the same parasite is the box‐nesting bird‐parasite system of eastern bluebirds ( Sialia sialis ) and tree swallows ( Tachycineta bicolor ) and their parasitic nest flies Protocalliphora sialia (DeSimone, Clotfelter, Black, & Knutie, ; Hannam, ; Roby, Brink, & Wittmann, ). While adult flies are nonparasitic, the larvae live in the nest and feed nonsubcutaneously on the blood of nestlings (Boyd, ).…”

“…For a potential mechanism of resistance, we quantified IgY antibody levels as a proxy of the immune response and then determined whether parasite abundance was related negatively to antibody levels (Owen et al, ). After the host is bitten, a series of immune pathways are activated by the host to induce the inflammatory response, leading to the production of IgY antibodies, which can bind to larval parasitic nest flies (DeSimone et al, ; Koop, Owen, Knutie, Aguilar, & Clayton, ; Owen et al, ). These immune molecules can negatively affect ectoparasites by causing edema (tissue swelling), which prevents the parasites from feeding from the capillaries, and damage to the parasite's tissue (e.g., via the release of proteolytic molecules from granulocytes).…”

“…These immune molecules can negatively affect ectoparasites by causing edema (tissue swelling), which prevents the parasites from feeding from the capillaries, and damage to the parasite's tissue (e.g., via the release of proteolytic molecules from granulocytes). If swallows are more resistant to P. sialia than bluebirds, then we predicted that nestling tree swallows would mount a higher immune response compared to bluebirds and the immune response will be negatively correlated with parasite abundance (DeSimone et al, ). For mechanisms of tolerance, we quantified hemoglobin levels as a potential proxy for oxygenated red blood cells recovery (i.e., tissue repair), and parental provisioning rates to determine whether parents of parasitized nestlings were compensating for energy lost to the parasite.…”

Food supplementation affects gut microbiota and immunological resistance to parasites in a wild bird species

“…Nests were also assigned to the parasitized or non‐parasitized treatment when eggs hatched. The nestlings and top liner of the nest were removed to treat the nest with either water to allow for natural parasitism or a 1% permethrin solution (Permacap) to remove all parasites (DeSimone, Clotfelter, Black, & Knutie, ; Knutie et al, ). Nestlings never contacted the parasite treatment since the liquid was sprayed under the nest liner.…”