Early Rearing Conditions Affect the Development of Body Size and Song in Bengalese Finches

Abstract

Birdsong is an acoustic ornament. According to indicator models, a trait must be costly to act as an honest signal, but the potential costs of elaborate songs are still poorly understood. The developmental stress hypothesis suggests that learned song characteristics could be an honest indicator of early developmental conditions because the brain structures associated with learning songs are susceptible to early developmental stress, which could thus affect song development. Unlike previous studies of developmental stress that examined the effect of a stress hormone or restricted nutrition, we observed Bengalese finches under semi‐natural breeding conditions in captivity to investigate the relationship between early rearing conditions (e.g., brood size and sex ratio) and the subsequent variation in body size and song among individuals. Our results suggest that the early rearing environment directly affects body size and song complexity, whereas song output is determined mainly by body size. These results support the developmental stress hypothesis. Moreover, our findings are the first to show that developmental condition affects not only the number of note types but also the syntactical complexity of the song.

Differential allocation in relation to mate song quality in the Bengalese finch

“…domestica, belongs to the same family (Estrildidae) as the zebra finch, but shows opposite sex-specific vulnerability. We found that male chicks were more likely to suffer from sibling competition in larger broods than females (Soma et al, 2006), because of the relatively higher growth rate of males (Soma et al, 2007). Thus, in Bengalese finches, having sons is more expensive for parents, but might lead to a higher fitness return in exchange for considerable reproductive investment.…”

“…It has been shown in Bengalese finches that these song features reflect early developmental conditions when song learning takes place, but are not related to body conditions in adulthood (Soma et al, 2006). By contrast, song duration is more plastic within individuals, and is known to reflect the body size of individuals (Soma et al, 2006).…”

“…Observed moderate biases in hatchling sex ratio could be caused either by biases in egg sex ratio, or by sex-specific embryo mortality (Pike & Petrie, 2003). Considering that male chicks are more vulnerable than females in this species (Soma et al, 2006), it is possible that male embryos are also subject to sex-specific mortality under particular reproductive conditions (cf., Love et al, 2005).…”

“…The acoustic features of songs have been shown to reflect various properties of potential mates, such as early developmental conditions (Nowicki et al, 1998;Buchanan et al, 2003;Spencer et al, 2003;Soma et al, 2006;Zann & Cash, 2007), body condition (Lampe & Espmark, 1994;Hoi-Leitner et al, 1995;Kipper et al, 2006), genetic quality (Hasselquist et al, 1996), and parental care (Welling et al, 1997;Buchanan & Catchpole, 2000). Because these qualities and conditions of individuals are likely to affect their offspring either directly (e.g., through resource provisioning) or indirectly (i.e., genetically), the song quality of the father can be used as a factor to predict offspring fitness.…”

“…In addition, female zebra finches have been shown to prefer males that sing longer songs (Clayton & Pröve, 1989;Neubauer, 1999), suggesting that similar preferences for song bout length could also exist in our subject species. It has been demonstrated that song duration in the Bengalese finch reflects body condition (Soma et al, 2006).…”