Abstract:
Physiological stress responses are essential to vertebrate survival. However, the strength of stress responses differs among individuals, even within the same species, population and sex. Differential stress reactivity can provide selective advantages depending on ecological context. In songbirds, individual quality can be honestly reflected through song quality, as factors like long-term stress and reduced energy reserves can reduce individual song quality. Variation in song is well-studied in males and likely shows similar patterns in females, but female song is poorly researched. My research examines how individual stress reactivities and sex interact with short-term stress to alter song complexity in adult songbirds.
I investigated these relationships using wild-caught common mynas (Acridotheres tristis), scoring individual stress reactivity, measuring physiological stress and recording vocalisations at baseline stress. Then the birds were fed corticosterone (CORT) to simulate a short-term stress response, and I measured changes in stress, behaviour and vocalisations. Stress was measured using faecal CORT and eye temperature with a thermal imaging camera, a new non-invasive stress measurement method. To quantify stress reactivity, I conducted three neophobia tests and rated behavioural stress during handling. I created a stress reactivity score using a principal component analysis of those measures. Eye temperature significantly increased after CORT ingestion, measured through a thermal camera, and was correlated with faecal CORT concentrations, indicating it is an effective estimate of stress response.
Simulated short-term stress significantly increased singing activity and song complexity, potentially indicating an adaptive response to CORT activation. Individuals that were more stress reactive (behaviour and handling) had smaller physiological responses to CORT treatment but more complex songs and higher singing activity. Males had higher song complexity during baseline conditions, but female songs became similarly complex when CORT was elevated. The effects of stress reactivity on singing were sex-specific in many parameters, raising many interesting questions for future research.
My research findings illustrate that individual differences in responses to stressors, such as ecological disturbances, can have substantial consequences for other, seemingly unrelated but ecologically relevant traits (singing) and also identifies new avenues for research on sex-specific relationships between stress and song. These findings are essential as stress-inducing disturbances increase in frequency under a changing climate.