The common raven is a native bird of high intelligence that adapts well to human disturbance and habitat fragmentation. Ravens prey on sage-grouse eggs and chicks, and consequently they may directly impact a species that DOE-ID is striving to conserve in partnership with other federal and state agencies. Raven observations made during annual breeding bird surveys have been steadily increasing over the past 30 years, mirroring trends across western North America.
The sage-grouse CCA describes predation threats associated with what appears to be a growing raven population on the INL Site. Our current understanding of raven population trends on the INL Site is based solely on breeding bird surveys that have been conducted most years since the mid-1980s. The weakness of this approach is that the breeding bird surveys count all ravens, but territory-holding ravens (i.e., nesting pairs) probably are responsible for the majority of sage-grouse nest depredation. On the INL Site, most ravens nest on man-made structures, such as power lines, towers, and building platforms, rather than on natural substrates, such as cliffs and trees. To better track the raven population trend as it relates to sage-grouse predation and to evaluate the influence of infrastructure on raven nesting, the ESER program annually surveys all infrastructure on the INL Site multiple times and documents active raven nests. This monitoring program has now been fully operated for two years. If results confirm that raven use of infrastructure as nesting substrates is expanding, DOE-ID may experiment with nest deterrent devices that discourage raven nesting in high-priority sage-grouse habitat.
During 2014 and 2015, we searched throughout April and May for raven nests along 197 miles of power lines, within 11 facilities, and at 11 towers on the INL Site. We found 37 nests in 2014 and 39 in 2015. In both years, the majority of nests (n = 31) were on power lines, primarily the two-pole transmission structures (Figure 1). In 2015, a raven pair nested at a majority (n = 6) of facilities and on two remote weather towers. In response to these data, ESER has begun working with the National Oceanic and Atmospheric Administration to install wire mesh on meteorological towers to discourage raven nesting. In its annual report, DOE-ID committed to the USFWS that they would search for cost-effective ways to reduce raven nesting within facilities, though no specific actions have been identified. INL Power Management is exploring installation of nest deterrent devices while performing routine maintenance. ESER will continue to work closely with DOE-ID and contractors to reduce opportunities for raven nesting on INL Site infrastructure.