LEVIN, R.N.*; CORREA, S.M.; WILL, M.C.; JANG, S.C.; Pomona College, Claremont, CA: Effects of Latitude and Altitude on House Wren Reproductive Biology

We are exploiting the broad distribution of the house wren to test hypotheses addressing environmental influences on mate fidelity and the hormonal control of reproductive behavior. Here, we present breeding data from two populations of northern house wrens (Troglodytes aedon) in the Sierra Nevada mountains (38° N, 2164m and 2521m), and two populations of southern house wrens (T. musculus) in Costa Rica (10° N, 35m and 1342m). Most studies of house wrens have been conducted on north temperate populations at relatively low elevations (e.g. 225m). In comparison, house wrens in the Sierras had a shorter breeding season, longer incubation and nestling periods, and lower rates of polygyny and double-clutching. Clutch size was similar to that reported elsewhere, although birds at our higher site showed a tendency to have smaller clutches in cold, wet years. The length of incubation and nestling periods did not differ between the two sites, suggesting that birds may reduce clutch size only after the period of parental care is increased in response to severe environments. Compared to northern house wrens, southern house wrens had longer breeding seasons, higher predation rates and smaller clutches. Incubation was longer in the tropical populations than it was in the Sierras, but the nestling period did not differ among the four populations. The two tropical sites did not differ in clutch size or duration of the nestling period, but incubation was longer at the higher site. Thus, in contrast to previously studied populations, parental care was prolonged for both tropical and high altitude north temperate house wrens. Because of the close genetic relationship between northern and southern house wrens, these data provide unique insights into hypotheses on life history variation.