Midwinter Raptor Counts

Each January, hundreds of volunteers and wildlife professionals throughout the United States count eagles along standardized, non-overlapping survey routes as part of the Midwinter Bald Eagle Survey (Steenhof et al. 2008). These annual surveys commenced in 1979 and today are managed by the U.S. Geological Survey (USGS). The Midwinter Bald Eagle Surveys were originally established to develop a population index of wintering bald eagles in the lower 48 states, determine bald eagle distribution, and identify previously unrecognized areas of important winter habitat (Steenhof et al. 2008).

Raptor CountOn the INL Site, Midwinter Bald Eagle Surveys have taken place since 1983. In early January of each year, two teams drive along established routes across the north and south of the INL Site and record the number and locations of all bald and golden eagles that they see. Observers also record the same information for other raptors, common ravens, shrikes (Lanius spp.), and black-billed magpies they observe along each route. Data are submitted to the regional coordinator of the USGS Biological Resource Division to be added to the nationwide database.

2015 Midwinter Eagle Count Results

On January 13, 2015, ESER biologists led surveys along the two traditional INL Site routes. Observers counted 98 birds (Figure 1), which was lower than what is typically seen (median=118) and was the fifth-lowest count in the past 15 years. Annual one-day counts are highly variable (range: 73–484 since 2001), and thus a single low year is not cause for alarm. The common raven was the most common species seen (n = 67), accounting for over two-thirds of all observations. Consistent with past years, the rough-legged hawk, which moves south to winter in the region, was the most frequently observed bird of prey (n = 21). Rough-legged hawk observations have been an order of magnitude higher as recently as 2010, but the average over the past four years was only 19. The species’ winter abundance on the INL Site may be cyclic (Figure 2), and past data would suggest that rough-legged hawk abundance will increase in the next year or two. Figure 1 Figure 2

Cumulative data from past surveys