PS 46-113 - Predictors of reproductive success in Dark-eyed Juncos (Junco hyemalis)

Background/Question/Methods

Bird song is a male sexual trait that can communicate aspects of the signaler's quality to prospective mates and potential rivals. Song traits that are physically challenging to produce and thus subject to performance constraints can enforce signal honestly, and these, together with nest habitat characteristics and weather variables, can influence the reproductive success of birds. We tested whether any of these predictors are associated with reproductive success in male Dark-eyed Juncos (Junco hyemalis). We recorded the songs of previously banded males, located their nests, and counted the number of eggs hatched and the number of nestlings fledged from each nest during the 2018 and 2019 breeding seasons. After the nestlings left the nest, we compared the temperature inside the nest to the ambient temperature to determine whether nests provide a thermal advantage. We also measured the surrounding stem density, canopy cover, average foliage cover, average nest exposure, and the distance of the nest to the closest trail. We obtained temperature measurements for the nesting period and then calculated average temperature and average minimum temperature during the nesting period.

Results/Conclusions

Individual Dark-eyed Juncos have a small repertoire of trilled songs, but among members of the same population, song diversity is high, and song type sharing is low. We did not find evidence of a performance constraint on song traits, and average reproductive success per nesting attempt was not related to any measure of song structure (frequency bandwidth, trill rate, song duration) or body size. Preliminary data suggest that egg hatching success and nestling survival are associated with nest habitat characteristics and the minimum temperature experienced during the nesting attempt. We, therefore, suggest that the reproductive success of these ground-nesting songbirds depends more on nest habitat characteristics and temperature during the nesting period than on male phenotypic traits.