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

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.

本研究针对外寄生性丽蝇（Protocalliphora sialia）的侵染，探究了雏鸟与成体树燕（Tachycineta bicolor）的规避、耐受与抗性策略。繁殖季早期，树燕会避开在朝北的巢箱中筑巢；此类巢箱在繁殖季后期更易被丽蝇侵染，这表明巢箱选择或可助力树燕实现丽蝇规避。本研究通过实验操控丽蝇侵染强度后发现，雏鸟整体上对丽蝇侵染表现出耐受：丽蝇侵染会显著降低雏鸟的血液血红蛋白水平，但对雏鸟体重、初级飞羽生长、离巢日龄以及离巢成功率均无显著影响。受侵染雏鸟的亲鸟并未提高食物投喂速率以增强雏鸟的耐受能力。成体雌性树燕同时表现出耐受与抗性：丽蝇侵染对成体的血红蛋白水平与体重无显著影响，且体内抗P. sialia结合抗体水平更高的个体，其巢内的丽蝇幼虫数量更少。雏鸟的抗体水平与丽蝇侵染强度并无关联。尽管各年份间存在较大差异，本研究结果表明，丽蝇侵染对树燕雏鸟与成体的生存代价较为有限，仅会造成雏鸟的血液流失。未来的研究可探究血红蛋白水平降低对雏鸟存活的影响，以及寄生特异性抗体的重要性。