Demography of White-Crowned Sparrows (Zonotrichia Leucophrys Nuttalli)

Abstract

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 nestlings 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%.

Temporal Estimates of Effective Population Size in Species With Overlapping Generations

“…Humans are a classic type I survivorship species, with high survival well into adulthood followed by a period of rapidly increasing mortality. The white-crowned sparrow (Zonotrichia leucophrys nuttalli; Baker et al 1981) has a modified type II survivorship curve, with a constant survival rate after an episode of high early mortality. The barnacle (Balanus glandula; Connell 1970) exhibits a classical type III survivorship curve with very high early mortality, even after we reduced fecundity and age-1 mortality by an order of magnitude from published values to make the simulations more tractable.…”

“…The small and large N 1 values were: human, 10 2 , 10 3 ; sparrow, 10 3 , 10 4 ; and barnacle, 10 5 , 10 6 (Table 3). These population sizes translated into N e values of order 10 2 for the small population sizes and of order 10 3 for the large population Table 5-2); white-crowned sparrow, modified from Baker et al (1981); barnacle, modified from Connell (1970). Ages are 5-year units in humans and 1 year in the other two species.…”

Population Dynamics in Variable Environments

“…This result indicates that it is important to determine whether life histories are differentially sensitive to a given amount of environmental variability. Acquisition of such data and information on temporal variability of vital rates (see Baker et al 1981 for a rare example) should be an important goal of experimental evolutionary genetics. There is no consistent relationship among life histories with respect to the coefficients of variation allowing neutrality.…”

Darwin's Finches (Geospiza) On Isla Daphne Major, Galapagos: Breeding and Feeding Ecology in a Climatically Variable Environment

“…There must have been a high mortality among females that were not recorded breeding in 1976, and hence were probably immature then, because the overall sex ratio in January 1978 was 6:1 (Table 8). The large variation among years and among different groups of finches makes it difficult to apply traditional demographic techniques such as life table analysis (Lack 1966, Ricklefs 1973, Baker et al 1981. Between March 1976 and January 1979, the mortality of 1976 juveniles was much greater than that for 1973 males (Fig.…”