Nest Success, Behavior, and Disturbance of Two Nightjar Species in Western Montana (Poster)

Abstract

The Common Poorwill (Phalaenoptilus nutallii) and Common Nighthawk (Chordeiles minor) are two nocturnal species breeding in western Montana. These ground-nesting insectivores deploy similar reproductive strategies, but have unique behavioral adaptations for nest success. From 2015-2018, we used cameras and monitoring to document phenology, disturbance, and success at 20 Common Poorwill and 14 Common Nighthawk nests. Poorwills arrived from mid-April to May, and laid their first eggs in May to early June. Nighthawks arrived a full month later, and initiated nests soon after arrival. Both sexes of poorwills incubate, brood and feed chicks. Poorwills often had two nests per breeding season. In contrast, just female nighthawks performed nesting duties, and their late arrival allowed for only one nest in a season. We documented disturbances from six different intruder types, from insects like grasshoppers, to rodents like chipmunks. We observed nine behavioral responses to intruders, including flushing off the nest, defensive posturing, and standing over or beside the nest. Poorwill and nighthawk nests were disturbed most by humans, unknown intruders, and rodents. Poorwills were most likely to flush off of nests upon disturbance, while nighthawks often defended the nest with aggressive posturing. Of the nests that we could determine fate, we confirmed failure at eight poorwill (40%) and two nighthawk (12.5%) nests. Most poorwill nests failed when nestlings were left unattended by adults. We don’t know what caused nighthawk nest failure. Future monitoring may give more understanding of how nest disturbances impact nesting success in both poorwills and nighthawks.