Colourful males hold high quality territories but exhibit reduced paternal care in barn swallows

Abstract

The European barn swallow, Hirundo rustica rustica, is a model system of female mate choice for indirect benefits. Its long tail, which is the target of female mate choice, is positively related to the genetic quality of males, whereas direct benefits in terms of territory quality and paternal care are unimportant in the choice of long-tailed males. However, the situation may differ in other subspecies where male ornaments other than tail length are elaborate and appear to be the main target of female choice. Here we studied whether throat colouration, a sexually selected trait, provides direct benefits in terms of territory quality and parental care in a population of Japanese barn swallows, H. r. gutturalis, which have short tails and large throat patches. We compared dyads of males occupying neighbouring territories to study the relationship between male ornamentation and territory quality in our sparse population. Males with higher quality territories had more colourful throat patches than males with lower quality territories, indicating a positive relationship between male throat colouration and the quality of their territory. In contrast, male feeding rate decreased with increasing colourfulness of male throat patch without confounding with female feeding rate. These results are consistent with previous studies showing a positive association between plumage colouration and testosterone levels. The trade-off between the two direct benefits of mate choice, i.e., territory quality and paternal care, can explain sexual selection for colourful throat patches rather than long tails in our sparse outdoor population, a typical breeding habitat in Japan, whereas it predicts a reverse pattern in dense indoor populations as found in Europe.