EARLY ARRIVAL, INITIATION OF NESTING, AND SOCIAL-STATUS - AN EXPERIMENTAL-STUDY OF BREEDING FEMALE RED-WINGED BLACKBIRDS

Red-winged blackbirds (Agelaius phoeniceus) arrive at breeding sites several months before nests are constructed. Males in this highly polygynous species presumably return early to defend desirable territories. Females, however, also begin to arrive almost two months before nesting is attempted. Early return to breeding sites could enhance reproductive success by increasing a female's social status and thereby allowing earlier nesting. I measured the effect of experimentally delayed arrival on the timing of nesting, reproductive success, and social status of females. Birds were captured as they arrived in early spring and detained in an aviary. These experimental females were later released at their capture sites before control females began construction of nests; controls had arrived during the same period as experimentals but were not detained. Experimental females nested, on average, more than a week later than controls, although I could detect no effect of timing on reproductive success during this study. By manipulating arrival date, but not covariates of arrival time such as age or experience, this result indicates that timing of arrival directly influenced laying date. Delayed females were subordinate to control females with the same mate. This decline in social status may have been responsible for the delay in nesting and could have fitness consequences for females in some years, because the offspring of earlier nesting, dominant birds are more likely to receive male parental care in this population.