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Breeding bird communities and habitat associations in the grasslands of the Chilcotin Region, British Columbia Hooper, Tracey D


The objectives of this study were (1) to characterize breeding bird communities in the grasslands around Riske Creek, in the Chilcotin Region of British Columbia, (2) to identify associations between grassland habitat characteristics and breeding bird diversity and species abundances, (3) to determine the relationship between food resource availability and grassland bird diversity and species abundances, and (4) to elucidate the potential impacts of livestock grazing on breeding birds and their grassland habitats. Point—counts and spot—mapping methods were used to census birds. Habitat characteristics measured were vegetation height, vertical cover, and patchiness, horizontal cover of different physiognomic features, arthropod abundances, and site slope, aspect, elevation. The season, intensity, and grazing by livestock and California bighorn sheep within th study area were also determined. Principal component, multiple correlation, and cluster analyses were used to analyze bird/habitat associations. Eleven species of birds were common throughout the study area. They were, in order of decreasing abundance: horned lark (Eremophila alestris), vesper sparrow (Pooecetes gramineus), European starling (Sturnus vulgaris), western meadowlark (Sturnella neglecta), long—billed curlew (Numenius americanus), Brewer’s blackbird (Euihagus cyanocephalus), tree swallow (Tachycineta bicolor), mountain bluebird (Sialia currucoides), American crow (Corvus brachyrhynchos), savannah sparrow (Passerculus sandwichensis), and red crossbill (Loxia curvirostra). Three red—listed (i.e., threatened or endangered) species (upland sandpiper (Bartramia lonciicauda), Sprague’s pipit (Anthus spragueii), Brewer’s sparrow (Spizella breweri)) and two blue-listed (vulnerable) species (sharp-tailed grouse (Tympanuchus phasianellus) and short—eared owl (Asio flammeus)), were also recorded. Over 13 study sites, bird density ranged from 0.82 to 1.24 pairs/ha and Shannon’s species diversity indices ranged from 0.71 to 1.38. Vegetation structure and patchiness, horizontal cover, topographic features, and grazing characteristics combined, explained 15-96% of the variability in bird diversity and species abundances. Topographic features were most often associated with bird diversity and species abundances, possibly due to correlations between topography and vegetation structure. Vegetation structural components were the second most common features associated with birds. Although arthropod abundances explained 15—72% of variability in bird diversity and species abundances, associations between birds and food resources were often unclear. Associations between birds and grazing were also unclear.

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