Effect of acute stressor on reproductive behavior differs between urban and rural birds

The life-history trade-off between self-maintenance and reproduction posits that investment in one function decreases investment in the other. Manipulating the costs and benefits of functions involved in a trade-off may alter this interaction. Here we ask whether investment in self-maintenance during a stress response alters territorial behavior in wild Dark-eyed Juncos and whether rural and urban birds, which are known to differ in the magnitude of the stress response (greater in rural), also differ in the degree to which stress reduces territorial behavior. In rural and urban habitats, we measured territorial behavior using song playback, followed by either an acute stressor (capture and collection of a blood sample) or a nonstressful control situation. The following day, we again measured territorial behavior, predicting greater reduction in territorial behavior in individuals exposed to the stressor but a lesser reduction in territorial behavior in the urban as compared to the rural environment. We further assessed individual and population differences in response to stressors by measuring flight initiation distance, breath rate, and corticosterone levels in the blood. The rural population had a higher physiological and behavioral stress response than the urban population, and acute capture stress had a lasting (24 h) negative effect on territorial behavior, but only in the rural habitat. However, individual-level differences in measures of the stress response did not explain variation in the impact of stress on territorial behavior. Our findings show that stressors can have a negative effect on territorial behavior, but that this effect may differ between populations that vary in their stress ecology.

自我维持与繁殖之间的生活史权衡理论认为，对某一项功能的投入会降低对另一项功能的投入。操控权衡所涉功能的成本与收益，或可改变这一互动关系。本研究旨在探究两个问题：其一，野生暗眼灯草鹀（Dark-eyed Juncos）在应激反应中对自我维持的投入，是否会改变其领域行为；其二，已知应激反应强度存在差异（农村种群应激反应更强）的城乡鸟类，在应激降低领域行为的程度上是否也存在差异。我们在城乡生境中，通过鸣放鸣唱回放录音来测定领域行为，随后分别施加急性应激刺激（捕捉个体并采集血液样本）或非应激对照处理。次日再次测定其领域行为，我们预设：接受应激刺激的个体，其领域行为下降幅度更大；且相较于农村种群，城市种群的领域行为下降幅度更小。此外，我们通过测定飞行起始距离、呼吸频率与血液皮质酮水平，评估了个体与种群间的应激反应差异。结果显示，农村种群的生理与行为应激反应均强于城市种群；急性捕捉应激会对领域行为产生持续24小时的负面影响，但该效应仅存在于农村生境中。不过，应激反应各项指标的个体间差异，无法解释应激对领域行为影响的变异程度。本研究结果表明，应激刺激可对领域行为产生负面影响，但该效应会因应激生态学特征存在差异的种群而有所不同。