Impacts of Supplemental Feeding on Survival Rates of Black‐Capped Chickadees

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Abstract
The availability of winter food may strongly influence overwinter survival and, hence, limit certain bird populations in northern regions. Using the Jolly—Seber method of estimating survival rates from recapture and reobservation data, we compared the survival rates of 418 individually marked Black—capped Chickadees, Parus atricapillus, having access to supplemental food with those of 158 chickadees without access to supplemental food. During three winters (October through April, 1982—1985) chickadees with access to supplemental food had higher average monthly survival rates (95 vs. 87%), higher overwinter survival rates (69 vs. 37%), and higher standardized body masses (an additional 0.13 g) than birds on control sites. Differential survival occurred primarily during months with severe weather (> 5 d below —18°C). During these months, high energy demands probably made it difficult for birds without access to supplemental food to obtain sufficient energy from dispersed natural sources. In addition, during periods of extreme weather when foraging may be difficult, the extra fat carried by individuals that are supplementally fed may increase the probability of survival.