Factors Affecting the Survival of Ovenbirds Wintering in the Northeast

The northern limit of the usual winter range of the Ovenbird (Seiurus aurocapillus) is coastal North Carolina (ca 36 degree N latitude; Root 1988a), with casual winter occurrences as far north as the Great Lakes region and New England (AOU. 1983). In general, the Ovenbird does not winter in areas where the average minimum January temperature is less than about 0 degree C and it is most abundant where this temperature is about 10 degree C (i.e., southern Florida). On 4 Jan. 1983 an Ovenbird appeared outside the bird banding laboratory at Powdermill Nature Reserve, Carnegie Museum of Natural History's field research station, three miles south of Rector, Westmoreland County, Pennsylvania (40 degree 10'N, 79 degree 16'W). In the mountain valley in which Powdermill is situated, minimum January temperatures average < -5 degree C and regularly drop below -17 degree C. We used our observations of foraging behavior and body mass variation in this bird, correlated to local weather data, to assess possible factors affecting the survival of individuals that attempt to winter north of the usual winter range of this species.