Evaluation of current agricultural practices and organophosphorus insecticide use in relation to ring-necked pheasant numbers at Klamath Basin Refuges, California Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9w0325457

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  • A declining population of ring-necked pheasants (Phasianus colchicus) was studied at Tule Lake National Wildlife Refuge (TLNWR) from the summer of 1990 through the spring of 1993. Pheasant densities/50 ha at TLNWR in 1989, 1991, and 1992 were considerably lower (16.86, 8.49, and 6.81) than the >62 density seen in the mid-1950s. Mean body weight of hen pheasants at TLNWR was significantly lower than hens at nearby Lower Klamath National Wildlife Refuge (LKNWR) which was not intensively farmed. Mean tarsal lengths of hens at TLNWR were also significantly shorter than hens at LKNWR, suggesting reduced skeletal growth and potential nutritional problems. The lack of adequate cover was responsible for poor early nest success at TLNWR. Later in the season, spring planted crops provided adequate cover to conceal nesting hens; however, only 0.21 young in 1991 and 0.02 young in 1992 were produced per radio-equipped hen. These rates are extremely low compared to rates required to maintain a stable population. Most adult mortality occurred during the spring and early summer months at TLNWR before crops provided adequate cover, and long before pesticide applications. The main predator of the pheasants was the golden eagle (Aquila chrvsaetos). Of special concern at TLNWR was pheasant and other wildlife exposure to anticholinesterase (antiChE) insecticides used on agricultural croplands at the refuge. Direct toxicity of antiChE compounds (in this case methamidophos) killed 2 young pheasants, but no adult radio-equipped hens died as a direct result of insecticide intoxication. This finding was of particular interest because 15% of the adult pheasants collected in and around potato fields had 55% brain ChE inhibition. The extent of the effects of insecticide exposure on the survivorship of pheasant young was uncertain as they were not radio-equipped. The overriding factor impacting the pheasant population at TLNWR and to a lesser extent LKNWR was poor habitat, especially in the spring when most mortality occurred. The poor habitat also resulted in extremely low recruitment (up to 1 September). Nearly all adult mortality and most of the low recruitment occurred before the insecticide spray season. The population was nearly extirpated during the severe winter of 1992-93.
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