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Demography of White‐Crowned Sparrows (Zonotrichia Leucophrys Nuttalli)
Author(s) -
Baker Myron Charles,
Mewaldt L. Richard,
Stewart Robert M.
Publication year - 1981
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1937731
Subject(s) - longevity , biology , avian clutch size , demography , juvenile , population , seasonal breeder , reproduction , zoology , ecology , genetics , sociology
Analysis of a White—crowned Sparrow population in coastal California resulted in estimates of the magnitude of variation in longevity (a) among cohorts in the same breeding season, (b) between sexes, and (c) between years. Mean longevity calculated from early juvenile life averaged °13 mo whereas mean longevity calculated from the egg stage was °6 mo. Survival of fledglings to 1 January was generally lower and more variable among cohorts than survival beyond January as adults. Reproductive information from a sample of known—age females indicated that clutch size and number of nestling increased with female age. Age—specific longevity and clutch size were combined to calculate the net reproductive rates of two female cohorts. These were 1.042 and 1.025, respectively. A combination of survival information from five cohorts and information on the numbers of males and females in reproductive condition suggested an effective sex ratio of one male per 1.2 females. This departure from strict monogamy reduces the genetically effective population size by 10%.