Singing on the nest: The occurrence of a paradoxical behavior

Background/Question/Methods

Bird song serves numerous functions, including attracting mates, obtaining and maintaining territories, and retaining mates, all of which contribute to reproductive success.  A potential cost of singing is the risk that vocalizations may give away an individual’s location to predators.  Bird nests are not mobile and so any attention drawn to a nest can increase the likelihood of the nest being discovered by predators.  Nest predation has been hypothesized to be a major force structuring bird communities and thus anything that increases nest predation should be strongly selected against.  A bird that is sitting on a nest therefore should not sing.  The phenomenon of singing on the nest should be extremely rare, but it is not well studied.  In this study, we investigated the frequency of singing on the nest by the Northern Mockingbird (Mimus polyglottos).  We obtained video footage of 128 nests to quantify the occurrence of this behavior.  Videos were randomly sampled for singing on the nest; in addition a custom Python program was written to comprehensively sample these video files by automating the process of reading large sound files and detecting potential singing times.

Results/Conclusions

Random sampling revealed seven nests in which the female mockingbird was singing while incubating.  The average song duration was 80.19 +/- 15.1 seconds.  Five of these seven nests were in the incubation stage at the time of singing and two were in the nestling stage.  Three of the seven nests were depredated, three survived and fledged, and one was abandoned.  Songs are currently being processed with the custom program to detect more instances of this rare behavior.   As sample size improves we can document how frequently this behavior occurs, the occurrence of factors that correlate with the frequency of this behavior, and if predation rate is higher for nests where singing has occurred.