Survival and Mobility in a Population of Pacific Coast Song Sparrows (Melospiza melodia gouldii)

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Abstract
The records of 2522 song sparrows (Melospiza melodia gouldii) banded from May 1966-Dec. 1970 on a 200-ha coastal study area on Point Reyes National Seashore in California [USA] were examined to characterize survival, dispersal and home range. The minimum annual survival rates were 0.45 for adults and 0.20 for juveniles. The estimate for juveniles is less than predicted, suggesting that some (about 14% of those surviving) dispersed from the study area. The median dispersal distance of 36 juveniles was 225 m, compared with 185 m and 265 m for 2 other populations of song sparrows. About 78% of the Point Reyes juveniles dispersed less than 400 m, while 22% dispersed more than 500 m. Five juveniles not included in this sample moved from 1425 to 2175 m in their 1st yr, indicating that a few birds move much farther than most. These long distance dispersers probably maintain gene flow between populations. Home ranges were estimated by measuring the maximum distance between 2 recapture sites. Median values were 125 m for adult males and 162 m for adult females. The question of whether song sparrow variation is due primarily to natural selection or to genetic drift is discussed. Small effective breeding populations make drift a potentially significant factor, but the effects of dispersal may counteract it.