The effect of elk grazing intensity on vegetation structure and breeding bird abundance in the shrubsteppe of Grand Teton National Park, Wyoming

Authors(s): A. Chalfoun

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Publication Date: 0000-00-00

Type: annual report

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Abstract: Objectives Elk (Cervus elaphus) graze more intensively in certain areas of the shrubsteppe in Grand Teton National Park, Wyoming. This allowed examination of whether elk grazing intensity may lead to changes in shrubsteppe vegetation structure, including the presence of invasive weed species, and whether higher order effects were evident. Higher order effects were assessed by measuring the abundance of breeding bird species in relation to elk habitat use (as indexed by scat count surveys) and vegetation structure. Findings and Status High elk use areas were characterized by lower shrub cover (density) and height, with lower forb and grass cover and increased bare ground in the understory. Only one species of noxious weed (musk thistle; Carduus nutans) was detected during the study and at only 2 of 60 study sites that both experience relatively low ungulate use but that had localized anthropogenic soil disturbance. Total breeding bird abundance, avian species richness, and abundance of 5 of 6 individual bird species including the Brewer's Sparrow (Spizella breweri), Green-tailed Towhee (Pipilo chlorurus), Sage Thrasher (Oreoscoptes montanus), Western Meadowlark (Sturnella neglecta), and Brewer's Blackbird (Euphagus cyanocephalus) were inversely correlated to elk grazing intensity. By contrast, the abundance of Vesper Sparrows (Pooecetes gramineus) increased with higher elk use. Avian abundance and species richness were positively correlated with shrub cover, shrub height and percent forb cover. High elk use may thus impact breeding shrubsteppe bird communities by initiating changes to the shrub and forb layer, although direct causative links cannot be inferred from these data. An alternative explanation is that elk select areas with low shrub and forb cover. Regardless, in order to facilitate healthy populations of shrubsteppe birds, managers should focus on ways to maintain areas with high shrub density and structural complexity, and a dense forb layer. Delineating the appropriate habitat features necessary for breeding shrubsteppe songbirds is important because many species are exhibiting significant region-wide declines mostly due to habitat degradation and loss. Experimental studies are needed that demonstrate the link between grazing intensity and the effects on songbird habitat, and should include the evaluation of important fitness components such as avian reproductive success.

Keywords: animal, mammal, ungulate, Cervidae, elk, wapiti, Cervus elaphus, food, forage, grazing, bird, breeding, population, ornithology, Aves, Grand Teton National Park, habitat, Brewer's Sparrow , Spizella breweri, Green-tailed Towhee , Pipilo chlorurus, Sage Thrasher , Oreoscoptes montanus, Western Meadowlark , Sturnella neglecta, Brewer's Blackbird , Euphagus cyanocephalus, Vesper Sparrows , Pooecetes gramineus