Tick infestation of chicks in a seabird colony varies with local breeding synchrony, local nest density and habitat structure

Parasites are a major risk for group-living animals and seabirds are notoriously susceptible to ectoparasite infestations because they commonly nest in dense colonies. Ticks parasitize seabirds across all biogeographical regions and they can be particularly harmful to nestlings, but the ecological factors that affect their transmission to chicks are little studied and poorly understood. Here we show that abundance of tick larvae in blue-footed booby (Sula nebouxii) broods varies with local nest synchrony and density, and also with habitat structure: abundance increased with local breeding synchrony, was linearly and quadratically related to local nest density, and was highest toward the southern end of the study area which has suitable (boulder-rich) habitat for ticks. Also, with increasing chick age infestation first increased and then declined. The results of this study highlight how local physical and social environmental factors influence infestation of seabird nestlings by ticks.

寄生虫对群居动物构成重大威胁。海鸟素来极易遭受体外寄生虫侵染，这一点广为人知，原因在于它们通常营密集集群巢穴。蜱虫可在所有生物地理区域寄生海鸟，且对雏鸟的危害尤为显著，但目前学界对影响蜱虫向雏鸟传播的生态因子的研究仍较为匮乏、认知不足。本研究显示，蓝脚鲣鸟（Sula nebouxii）育雏群中的蜱幼虫丰度，会随当地巢群同步性、巢群密度以及生境结构发生变化：其丰度随当地繁殖同步性升高而增加，与当地巢群密度呈线性及二次相关关系，且在研究区域的南端——该区域拥有适合蜱虫生存的多砾石生境——达到峰值。此外，随着雏鸟日龄增长，蜱虫侵染程度先升后降。本研究结果揭示了当地物理与社会环境因子如何影响蜱虫对海鸟雏鸟的侵染情况。