Seasonal Changes in the Survival of the Black-Capped Chickadee

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Abstract
A population of black-capped chickadees living in a favorable environment was color-banded, and its survival on the study area was followed over a 2-year period. A weekly census of the population was made throughout the study. All nests were found, and the young were banded before they flew. Every 2 weeks throughout both winters checks were also made on an unbanded population in a "control" area one and one-quarter miles from the mam population. Nesting success was high in both years, with 5.00 young/pair being fledged in 1964 and 4.99 young/pair in 1965. Juvenile survival until family break-up was almost 100% in each year; juvenile survival until Sept. seemed to be high. Adult losses did not occur steadily throughout the year; rather there was a sharply defined period of high mortality, emigration, or both, at the time of the change from flocking to territorial behavior in the spring. With the exception of one unmated female in each year, every bird that remained after this critical period bred or attempted to breed; hence this change in behavior in the spring evidently removed surplus birds from the area, and thus prevented continual increase in the population. Breeding populations of other spp. with similar ecology, e.g. other members of the same genus, may also be limited by similar behavior patterns.