Relative breeding timing and reproductive success of a resident montane bird species

The phenological match-mismatch hypothesis predicts that animals that better synchronize critical life history events with the peak availability of their primary food source should have higher fitness. If phenological match-mismatch determines breeding success, most individuals in a population may be expected to breed simultaneously within a given year because selection has favored mechanisms that allow for the tracking of optimal food abundance. Therefore, individuals that breed too early or too late relative to the bulk of the population ("peak" of breeding) should experience decreased fitness. Using 11 years of data, we investigated the effect of relative breeding timing on breeding success in resident mountain chickadees (Poecile gambeli) across two elevations in the Sierra Nevada mountains, USA. Chickadees that bred during the peak of nesting did not have the highest breeding success; instead, birds that bred earliest performed best at high elevation, while at low elevation early and peak nests performed similarly. Breeding success decreased linearly with relative timing at both high and low elevations, and the relationship between breeding success and timing differed among years. Our results suggest that phenological match-mismatch may not be the main driver of within-year variation in breeding success in animals residing in montane environments.