Yasukawa Recent Projects
Do Nestling Red-winged Blackbirds "Blackmail" Their Parents into Feeding Them?
Emily Dorjath ('15), Steph Morgan ('15) and I have been testing predictions of the "blackmail" hypothesis for nestling begging calls. According to this hypothesis, because loud vocal begging attracts nest predators, parents are coerced into providing more food than is optimal for them to prevent their nestlings from being eaten by predators. We have been testing predictions of this hypothesis, but have found no evidence for this hypothesis. On the contrary, parents seem reluctant to feed their nestlings when they are at risk of predation and vocal begging does not increase the risk of nest predation.
Nestling begging in red-winged blackbirds
In conjunction with students Catie Anderson (’11) and Nicole Krauss (’11), I have been studying the begging behavior of nestling red-winged blackbirds and the feeding behavior of their female parents. We use HD video cameras to record interactions among nestlings and their mothers in the field at Newark Road Prairie. Nestling begging is likely to be an indication of need, so parents should respond to accurate signals of need by feeding needy offspring. Nestlings are also competing with their siblings, so their begging might also be an attempt to manipulate their parents into feeding them at the expense of their siblings.
Alarm calling and nestling begging in red-winged blackbirds
Jacy Bernath-Plaisted (’11) and I have studied communication between red-winged blackbird parents and their offspring by observing nestling begging behavior using video recording and performing a playback experiment using recorded alarm calls of males. Nestling begging includes both visual and vocal components, but loud begging calls might attract predators, which are the most common reason that redwing nests fail. Our observations and experiments were an attempt to see if alarm calling in response to the presence of a predator is a way to silence nestlings and thus reduce the chances that predators will find them.
Will Werner (‘08), Anthony Johannes (’09), Hazel Berrios (’11) and I have studied interactions between brood parasitic brown-headed cowbirds and their host red-winged blackbirds. Female cowbirds do not build nests and do not raise their own young. Instead they lay their eggs in nest of “host” species, which then raise the cowbirds. This arrangement is advantageous for the cowbirds, but not for the hosts, so cases of brood parasitism beg the question, why do hosts accept cowbird eggs and raise cowbird nestlings. We used video recordings and experimental additions of cowbird or redwing eggs to investigate brown-headed cowbird egg and nestling acceptance by red-winged blackbirds.
"Floating" versus territory defense in red-winged blackbirds
Male red-winged blackbirds are known for their vigorous defense of breeding territories, but despite their best efforts, territorial males do not maintain completely exclusive access to their defended areas and they father only a portion of the young on their territories. Trespassing by other males is common and most of these trespassers are "floaters" that wander widely in search of opportunities to secure their own territories. In addition, about a third of all red-winged blackbirds are fathered by males other than the territory owners ("extra-pair young"). I compared the responses of territory owners and floaters to a stuffed female red-winged blackbird mounted in the posture used to solicit mating from males ("copulation solicitation display"). Territory owners and males from neighboring territories readily courted and copulated with the stuffed female, although males with prior breeding experience were more likely to be "successful" than inexperienced males. Floaters also attempted to copulate, but young floaters (1-year-old) did not court and were mostly "unsuccessful," whereas older floaters (at least 2 years old) did court and were about as successful as inexperienced territory owners. Neighboring males are responsible for most extra-pair young, but floaters probably father young at least occasionally.