Reproductive ecology of Ferruginous Hawks in the northern Great Plains
Ferruginous hawks are a grassland/shrubland obligate nesting raptor and prefer lightly grazed pasture or idle areas for nesting. In the Dakotas, they are residents of short- and mixed-grass prairies that represent the eastern edge of their breeding distribution in North America. In the Great Plains, breeding range, local abundance, and reproduction of several populations of ferruginous hawk have declined and anthropocentric land-use changes potentially will continue to operate as a stressor. In 2013, we initiated a study to investigate the influence of local-and landscape-scale factors influencing the reproductive success of ferruginous hawks in pastoral western South Dakota (WD), and agricultural north-central South Dakota and south-central North Dakota (ED). Using ground and aerial surveys, we located and monitored nesting ferruginous hawk pairs and monitored them from March through August. We used program Mark to assess nest survival and nest success associations with landscape characteristics.
We located and monitored nesting ferruginous hawk pairs: 49 in 2013 (WD = 29, ED = 20) and 34 in 2014 (WD = 14, ED = 20), nesting declined by 52% in WD in 2014. Apparent nest success in WD was 55% (16 of 29) and 50% (7 of 14) during 2013 and 2014, respectively. In ED, apparent nest success during 2013 and 2014 was 67% (10 of 15) and 85% (17 of 20), respectively. Fledgling/successful nest was 2.5 (n = 38) and 1.6 (n = 11) in WD and 2.2 (n = 22) and 2.6 (n = 44) in ED in 2013 and 2014, respectively. In 2013 two nest mortalities (5 fledges total) in ED were attributed to WNV infection and E. coli septicemia. Survival was constant between years and study areas; estimated overall nest survival using Program MARK was 0.42 (SE = 0.06, 95% CI = 0.30–0.54). Nests had high (≥ 50%) association with herbaceous/pasture cover type. Nesting decline in WD and overall low nest survival may be associated with limited prey and continued conversion of grassland habitat in the Northern Great Plains. Populations which breed in such low densities are further threatened by emerging infectious diseases. Land-use and management practices on private land may have impacts on populations of grassland obligate species and mitigation is imperative.