Common Raven Abundance

Common Raven (Corvus corax) Abundance in Relation to Anthropogenic Resources within the Idaho National Laboratory Site in 2010

 

Objectives

This study examines how proximity to anthropogenic resources affects common raven abundance. Determining how anthropogenic resources influence raven density in sagebrush steppe habitat will provide Bureau of Land Management (BLM) land managers with information necessary to identify sources of human disturbance. Specific objectives include the following:

  • Calculate resource selection functions of habitat use for territorial and non-territorial ravens on the INL Site
  • Develop predictive model of broad-scale raven habitat use
  • Identify anthropogenic factors that affect raven presence.


Summary

Common raven (Corvus corax) populations in the western United States have increased substantially during the last 50 years. Ravens typically are more abundant in human-altered landscapes than in intact ecosystems. This is cause for concern among land managers because ravens are considered a synanthropic predator (a predator benefi ting from anthropogenic resources and land actions) of numerous sensitive species, including Greater Sage-Grouse (Centrocercus urophasianus) eggs and chicks. Increases in linear infrastructures (roads and power lines) are likely to further increase raven abundances and subsequently increase sagegrouse nest depredation by ravens. The potential for ravens to limit sage-grouse populations constitutes a need to assess the presence of ravens over large spatial scales within sagebrush steppe habitat.

 

For surveyed ravens, the simplest and most meaningful models included distance from transmission lines, facilities, and non-native grasslands. For every 1 km (0.6 miles) increase in distance to transmission lines and facilities, the odds of raven presence decreased by 9.3 percent and 4.5 percent, respectively. Also, for every 10 ha (25 acre) increase of non-native vegetation, the odds of raven presence increased by 2.7 percent. In post hoc analyses, the odds of raven presence increased with greater habitat edge length of big sagebrush (Artemisia tridentata spp.) and non-native vegetation.

 

For nesting ravens, the odds of nesting were greater with decreased distance to transmission lines and increased amount of vegetation type edge. For every 1 km (0.6 miles) increase in distance away from a power line there was a 37 percent decrease in odds of raven nesting. Habitat fragmentation indices were 3.1 times greater at nest sites than at random sites. For every 100 m (328 feet) of added vegetation edge, there was an estimated 20 percent increase in the odds of raven nesting.