Ecology of female northern pintails during winter in the San Joaquin Valley, California Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8k71nn375

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  • I radio-tagged 191 Hatch-Year (HY) and After-Hatch-Year (AHY) female northern pintails (Anas acuta) in the San Joaquin Valley (SJV), California and studied their movements, habitat use and survival during August March, 1991-94. Overall, 94.3% wintered in central California; the highest percentage left during the 1991 drought. Tulare Basin and Mendota Wildlife Area (WA) pintails moved to the Grassland Ecological Area (EA) vicinity when hunting began. Of those wintering in central California, 83% went to the Sacramento Valley, most during December. AHY pintails tended to leave earliest but the effect of age varied with body condition. Loss of Tulare Basin habitat has contributed to the late-winter decline of pintails throughout the SJV. Local distribution and movements differed most among seasons, day and night periods and shoot and nonshoot days. Overall, 64% of the day and 85% of the night locations in the Grassland EA vicinity were on private wetlands. Habitat availability and use varied greatly among SJV areas and during the winter. Pintails selected shallow and avoided deepwater habitats. Swamp timothy wetlands were the most abundant and most highly selected habitat in Grassland EA and Mendota WA. In Tulare Basin, preirrigated fields were the most abundant and selected habitat during PREHUNT, but managed wetlands were most abundant and selected thereafter. Selection of watergrass wetlands during night was low in the Grassland EA vicinity but high in Mendota WA. In Tulare Basin, pintails selected preirrigated fallow and safflower fields; selection of barley-wheat fields varied greatly. The exodus of most pintails from the SJV during December implies that preferred late-winter habitats were lacking. Winter survival was lower for HY (0.67) than AHY (0.76) pintails. Survival was similar to Louisiana and Suisun Marsh but lower than in the Sacramento Valley. Hunting caused 83%, avian predators 7.6%, collisions 1%, and disease or other non-hunting factors 8.7% of the mortalities. Hunting mortality was related to fall body condition for HY but not AHY pintails. The retrieval rate for shot radio-tagged pintails was 80.3%. This study indicates that inter-related factors influenced female pintail ecology during winter in California but availability of productive habitat was especially important.
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