科研之友
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摘要
Deciduous riparian ecosystems in the western United States provide habit it for m higher density of breeding birds than reported for any other win habit it type sod provide habit it for more breeding bird species than adjacent uplands On the east slope of the Sierra Nevada riparian ecosystems make up <1% of United States Forest Service lands vet experience a disproportionate amount of recreational use and development Two of these developments pack station corrals and campgrounds provide foraging opportunities for the Brown headed Cowbird (Molothrus ater)-an obligate brood parasite that forages on bare ground and feedlots but typically commutes to distinct shrubland or woodland habitats for breeding We examined nest survival brood parasitism breeding phenology and causes of nest failure for birds at North Lake and Rock Creek 2 high elevation (>2500 m) rip in in breeding habitats adjacent to recreational development and within cowbird commuting distance to additional potential foraging sites Nest survival tended to be higher for host species at Rock Creek than for those it North Lake but parasitism rates were not significantly different between plots Of 21 open cup nesting species 12 were parasitized We found the highest rate of parasitism (92%) for Warbling Vireos (Vireo gilvus) at North Lake and p parasitism contributed to lower total nest survival there (14%) For ne irk all species parasitzed nests were less successful and produced fewer young thin nonp prastized nests However pied thou was the leading cause of complete nest future across ill species mud contributed to the lowest total nest survival estimates for Western Wood Pewees (Contopus sordidulus 11%) and Duskv Flycatchers (Empidonax ober holseri 15%) it North Lake and for Dark eyed Juncos (Junco hyemalis 15%) at Rock Creek Nest sin-sisal was relatively high for Western Wood Pewees (41%) at Rock Creek and for Yellow Warblers (Dendrouca petechia 47%) at North Lake We noted whether the arrival of pack animals at pack station conals contributed to variation in cowbird numbers it cor rals or in parisitism rates it the 2 sites Cowbirds occupied corrals before and after pick stock arrival and most host dutches were completed prior to pack stock arrival at nearby corials suggesting that the presence of pack animals did not directly affect cowbird host species
- 出版日期2010-10
