Date of Award:

5-2015

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Michael R. Conover

Committee

Michael R. Conover

Committee

Shandra N. Frey

Committee

Eric M. Gese

Abstract

Common raven (Corvus corax; hereafter raven) populations have been increasing rapidly in the western United States, and these ravens cause damage to livestock, human health and safety, and wildlife species including greater sage-grouse (Centrocercus urophasianus; hereafter sage-grouse). The goals of my research were to gain a better understanding of the winter ecology of ravens, to see how raven populations were impacted by intensive removal during the winter, and to determine if raven removal aids sage-grouse populations. I found that ravens captured at landfills used these landfills sporadically for foraging, and these ravens regularly used bridges and industrial sites for roosting in the evening. Raven counts at anthropogenic roost sites and landfills fluctuated similarly when these locations were <15 km away from each other. In the spring, ravens dispersed, on average, 38 km from landfills where they were caught.

Raven removal applied during the winter may alleviate damage caused by ravens in the spring and summer months. I analyzed raven survival and behavior when USDA/APHIS Wildlife Services (WS) removed ravens using DRC-1339. I found that 7-34% of the raven population was removed annually from these efforts. Ravens did not avoid landfills after poisoning, but ravens switched roosts after a DRC-1339 application.

Recent studies have indicated that raven removal improves sage-grouse nest success. However, connections between raven removal and sage-grouse abundance have not been explored in detail. I analyzed changes in raven density with regard to WS removal, and then related changes in landscape raven density with changes in sage-grouse lek counts the following year. Raven densities decreased by 50% from 2008-2014 where WS removed ravens. Sage-grouse lek counts did not improve in areas where WS lowered the abundance of ravens, in comparison to areas farther away, until the latter half of the study (2013-2015) when raven removal increased. Thereafter, a 10% decline in raven numbers increased sage-grouse numbers by 2%.

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