Female Black-capped Chickadees eavesdrop on male song contests to make extra-pair mating decisions
Daniel J. Mennill
In many different animal species, males engage each other in elaborate signalling interactions. Songbird males interact with each other through song contests, which are common during the reproductive season. Other individuals may eavesdrop on male-male singing contests in order to assess the relative quality of the interacting parties. In particular, females may benefit by eavesdropping on males' interactions because eavesdropping provides a low-cost method of assessing male quality and comparisons between singing males may be made easily. My research focuses on female eavesdropping on male song contests in black-capped chickadees, and the consequences of female eavesdropping for female mating decisions.
Black-capped chickadees are monogamous songbirds. However, some females engage in a mixed mating strategy by having copulations with neighbouring males. When choosing copulation partners, females prefer males who have a high-ranking position in the previous winter's flock. As such, it is common to find nestlings that are not related to their social father in the nests of low-ranking males, but uncommon to find these extra-pair offspring in the nests of high-ranking males. I monitored a population of chickadees at Queen's University Biological Station, near of Kingston, Ontario, Canada, for three consecutive years. Throughout the non-breeding season I monitored chickadee interactions at feeding stations in order to establish which birds were low-ranking males and which males were high-ranking males. I used rank information to predict which males were likely to lose paternity within their nests (low-ranking males) and which males were not likely to lose paternity (high-ranking males).
During the chickadee breeding season I performed an interactive playback experiment. Using a library of songs stored on a laptop computer connected to a microphone and loudspeaker, I simulated a singing male intruding into breeding males' territories. I engaged some males in singing contests by mimicking a very aggressive territorial intruder, to create the impression that these males "lost" a song contest. I engaged other males in singing contests by mimicking a very submissive territorial intruder, to create the impression that these males "won" a song contest. In the weeks following playback experiments, I collected blood samples from the playback subjects' offspring. I found that high-ranking males who lost song contests also lost paternity in their nests. My results suggest that female black-capped chickadees eavesdrop on male-male singing contests and that the information females gain through eavesdropping plays an important role in shaping female
reproductive decisions.
I conducted this research under the guidance of Dr. Laurene M. Ratcliffe in the Biology Department at Queen's University. I conducted paternity analysis under the guidance of Dr. Peter T. Boag in Queen's University Molecular Ecology Lab. You can read more about this research at:
