PUB - Publikationen an der Universität Bielefeld

Plovers (subfamily: Charadriinae) are visual foragers that rely on ambient light for detection of invertebrates, as demonstrated by their foot-stirring behaviour used to stimulate a flight response in prey. At night, although ambient light is minimal, predation pressure from diurnal raptors is reduced and invertebrate prey availability increases, thus creating fitness benefits to nocturnal foraging by invertivores. The Killdeer (Charadrius vociferus) is a widespread yet understudied Plover that primarily inhabits agricultural fields throughout North America during the winter. Because nocturnal ambient light is directly dependent upon the lunar cycle, I hypothesized that Killdeer exploit nights with greater lunar illumination to be able to forage when predation risk is low and prey availability is enhanced. I predicted that nocturnal activities by Killdeer would be reflected in their diurnal behaviour the subsequent day, with decreased diurnal foraging following lighter nights. I also considered the additive effect of lower ambient temperatures and precipitation. I used an information-theoretic framework to compare these hypotheses and found the model with greatest support revealed a clear negative relationship between diurnal foraging and the amount of lunar illumination the preceding night. Interestingly, I found the opposite trend in diurnal roosting behaviour, suggesting that if nocturnal light levels suffice, Killdeer forage at night and roost during the day. I propose that this behaviour is driven by differential predation risk and food availability perceived by Killdeer at night vs. day. I also discuss the potential functional importance of energetic demands. Taken together, these results highlight the potential for avian diurnal behaviour to be closely tied to natural variation in nocturnal light availability, a finding with potential relevance to the increasing threat of artificial light pollution in our era of industrialization.