Graduate Thesis Or Dissertation
 

Distribution and mortality of the Pacific coast band-tailed pigeon

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  • A study of the Pacific coast Band-tailed pigeon (Columbia fasciata Say) was conducted from August 1966 to September 1968. Bands recovered from 14,787 pigeons banded in the Pacific Coast states, 1929-65, were used to determine distribution, migration, and mortality. Data on the age structure of populations were obtained from 3,596 pigeons killed by Oregon hunters in September 1966-67, 64 pigeons killed by California hunters in December 1966, and 1,799 pigeons trapped in Oregon during May and June 1967-68. The range of the band-tail extends along the Pacific coast from northern Baja California, Mexico to central British Columbia, Canada. Band recoveries indicate most pigeons left the wintering grounds in California by April 1. By June 10 nearly all pigeons reached the northern breeding grounds. Fall migration from the northern part of the range was well-advanced by mid- September. Estimates made by conservation agencies indicated the annual kill apprached 500 thousand pigeons. Approximately 50 percent of the kill occurred in California, 25 percent each in Oregon and Washington, and 1 to 2 percent in British Columbia. One-third of the adult pigeons shot in Oregon during early September were caring for young. Undoubtedly this resulted in the mortality of some young. The age structure of the Oregon kill was not representative of the population because some young were still in the nest and a differential in the migration of adults and immatures probably existed, The large percentage of subadults in spring populations indicated the kill was biased in favor of adults. The age structure of the kill on the wintering grounds in California was biased in favor of immatures because immatures were more vulnerable to hunters than adults. The average annual mortality for adults banded in the Pacific Coast states ranged from 31 to 39 percent. Immatures exhibited a somewhat greater mortality. A relatively small fraction, 26 to 43 percent, of the adult mortality was due to natural causes. This indicated that the majority of the mortality was a result of hunting. This study indicated an important need for the following research: (1) Determination of the magnitude or existence of differentials in mortality, vulnerability, and migration by age and sex for pigeons banded during July and August; (2) Determination of the significance of the loss of young due to the late nesting of some adults during the September hunting season.
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