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

Abstract

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.

Keywords: Aggression; behavioral plasticity; flexibility; global change; reproduction; stress.

Figure 1

Male Oregon Junco (Junco hyemalis).Photograph by Joseph Higbee.

Figure 2

Exposure to an acute stressor affects territorial behavior differently in rural and urban birds. Circles and error bars denote means and standard errors of territorial behaviors during the pretreatment and the post‐treatment STI in control (black) and acute stressor (gray) treatments. An acute stressor did not affect singing in either population (A, B), although rural birds sang more in general. Treatment did not have a significant effect on median approach distance in urban birds (C), whereas in rural bids, stress treatment led to an increase in median approach distance while control birds did not change their behavior (D). Stress treatment had a similar effect on approach time in both urban (E) and rural (F) populations – in both cases, birds exposed to the stressor approached the lure more slowly, whereas control birds approached the lure more rapidly. The stressor had a different effect on number of flights in urban (G) and rural (H) birds: in the urban population, birds from both treatments reduced number of flights, whereas in the rural population, control birds increased while birds exposed to the stressor decreased number of flights.

Figure 3

Stressor‐induced CORT is higher in the rural population than in the urban population. CORT values are corrected for the effect of date (both populations show decrease in stressor‐induced CORT (ng/ml) across the breeding season).

Figure 4

Breath rate after handling was higher in the rural than urban population. Graph shows means ± SEs. Points are jittered to aid interpretation.

Figure 5

FIDs were lower in the urban population compared to rural population in both adult (black) as well as juvenile (gray) birds. Graph shows individual data points and means ± SEs.