Upcycling in the Hawaiian Islands: Native Forest Birds Commonly Engage in Nest Material Kleptoparasitism

AbstractNest material kleptoparasitism, the theft of nesting materials by birds from other nests, is likely more widespread in passerines than currently documented. Yet no studies examine the hypotheses underlying when nest material theft will likely occur. Here we investigate nest material kleptoparasitism during the monitoring of 216 nests of passerines on the island of Hawai'i. Native Hawaiian forest birds were victims of nest material theft at a frequency correlated to their relative nesting abundance in the landscape. We provide the first evidence consistent with the height overlap hypothesis, demonstrating that Hawaiian forest birds stole material from nests in the same strata where they foraged for prey. Because 2 out of 39 (5%) of these events shortly preceded nest failure, we suggest that nest material theft, albeit small and previously overlooked, may be a contributing factor to nest failure. Future research should quantify key factors influencing this behavior, including types and relative abundance of materials stolen, timing, nest height, and impact on nest success.