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 s everal months before nests are constructed. Males in this highly polyg ynous species presumably return early to defend desirable territories. Females, however, also begin to arrive almost two months before nesti ng is attempted. Early return to breeding sites could enhance reproduc tive success by increasing a female's social status and thereby allowi ng earlier nesting. I measured the effect of experimentally delayed ar rival on the timing of nesting, reproductive success, and social statu s 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 ne sts; 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 timin g on reproductive success during this study. By manipulating arrival d ate, but not covariates of arrival time such as age or experience, thi s result indicates that timing of arrival directly influenced laying d ate. 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 s ome years, because the offspring of earlier nesting, dominant birds ar e more likely to receive male parental care in this population.