Will the intrusion of an avian nest predator elicit a change in the behavior of a canopy-nesting passerine?

Abstract

Based on Breeding Bird Surveys during the last several decades, the Cerulean Warbler (Setophaga cerulea) has shown severe population declines throughout its range and it is listed as endangered in the state of Indiana, and a species of special concern by the United States Fish and Wildlife Service. This study aimed at identifying aspects of Cerulean Warbler behavior that were previously unknown. Predators have the ability to influence behaviors of their prey directly through predation, and indirectly through short-term behavior modifications aimed at reducing detection opportunities. I simulated the intrusion of a nest predator (Blue Jay) in the territory of nesting Cerulean Warblers, using a combination of vocalizations and a stuffed specimen, and recorded 8 different behavioral variables to identify if there is a difference in their behavior, to avoid nest detection. The results of this study provide evidence that female Cerulean Warblers recognize Blue Jays as a potential nest predator by increasing their vigilance while on the nest. Females exposed to a nest predator increased the duration of their incubation bouts by 87% and brooding bouts by 63%. My data also suggests that male Cerulean Warblers reduce their provisioning rate during the early nestling stage (-2 feedings/hour) and late nestling stage (-5 feedings/hour). The Cerulean Warbler is a species that uses a wide range of tree species for nesting locations, but previously only deciduous tree species have been selected. In this study, we identified two separate Cerulean Warbler pairs building their nest in a coniferous tree (White Pine; Pinus strobus), suggesting that Cerulean Warblers likely do not select nest sites based on the tree species, but rather based on the microhabitat characteristics within the tree itself. Site fidelity is one aspect of Cerulean Warbler behavior that is relatively unknown. Since 2013, we have color banded 130 Cerulean Warblers, 10.8% of which have returned the following year. Age, sex, and nest success did not affect return rates. In a different study, we used light-level geolocation to identify migratory behavior of adult male Cerulean Warblers in southern Indiana. Since 2016, we have deployed 30 geolocators, 4 of which were recovered in the year following deployment. Cerulean Warblers occurred broadly throughout northern South America. Autumn migration lasted 44-71 days (n = 4), whereas spring migration lasted 37-41 days (n = 3). The average migration distance traveled was 5268 km. During autumn migration, Cerulean Warblers made 1-4 stopovers (i.e., ≥2 days; n = 4) and 1-2 stopovers during spring migration (n = 3). When crossing the Gulf of Mexico during autumn migration, two birds stopped over after crossing, but not beforehand. Two others navigated through the Caribbean rather than crossing the Gulf of Mexico. During spring migration, one individual stopped after crossing, one individual stopped before crossing, and one individual stopped before and after crossing the Gulf of Mexico.