Dissertation - Open Access
Doctor of Philosophy (PhD)
Natural Resource Management
Jonathan A. Jenks
ferruginous hawk, golden eagle, nest-site selection, nest survival, northern harrier, raptor
Ferruginous hawks (Buteo regalis) are a grassland and shrubland obligate nesting raptor and prefer lightly grazed pasture or idle areas for nesting. Their population reportedly declines in number if more than 30% of an area is cultivated and they rarely nest in areas dominated by croplands. Golden eagles (Aquila chrysaetos) are long-lived raptors with high nest-site fidelity and relatively low reproductive success. Population trends of golden eagles in western United States are unclear although long-term monitoring of populations shows declines in occupancy and breeding performance. Northern harriers (Circus cyaneus) prefer relatively open grasslands and wetland areas of various natures. During the breeding season from 2013–2015, we investigated the influence of factors associated with the landscape on survival and nest-site selection of ferruginous hawks, golden eagles, and northern harriers in the northern Great Plains (north-central South Dakota, south-central North Dakota hereafter, Eastern Dakota [ED], and northwestern South Dakota hereafter, Western Dakota [WD]). Using ground and aerial surveys, we located and monitored active ferruginous hawk, golden eagle, and northern harrier nests (ferruginous hawk, n = 55; golden eagle. n = 35; northern harrier, n = 22). In ED, one pair of ferruginous hawk was found every 655 km2. In a more suitable subset of 4420 km2 in ED, we found one pair per 340 km2. In WD, we documented one breeding pair in 315 km2. In ED, all ferruginous hawk nests were in trees, and apparent nest success was 62% in 2013, 94% in 2014, and 87% in 2015. In WD, apparent nest success was 62% in 2013, 43% in 2014 and 94% in 2015. Overall, 101 ferruginous hawk chicks fledged in ED; 2.4 fledglings/successful nest, and 100 chicks fledged in WD; 2.6 fledglings/successful nest. In WD golden eagle pairs were documented with one nest every 1740.4 km2 for the duration of the study. Active nests of golden eagles were placed on two different substrates (i.e., steep cliff-side [n = 5] and trees [n = 30]) and apparent nest success was 62% in 2013, 94% in 2014, and 87% in 2015. Overall, 41 golden eagle chicks successfully fledged; 1.4 chicks/successful nest (SE = 0.09). Cottonwood (Populus deltoides) was the sole tree of choice for nesting golden eagles in WD (n = 30) followed by steep cliff-side (n = 5). No golden eagle nest was documented in ED. During breeding seasons in 2013 and 2014, one breeding pair of northern harrier was found every 370.6 km2. Most northern harrier nests were in seasonal or permanent wetlands with cordgrass (Spartina spp; n = 12), bulrush (Scirpus spp.; n = 6), cattail (Typha spp.; n = 3), and residual corn (Zea mays; n = 1). Apparent nest success was 25% in 2013, and 70% in 2014. During the 2013 breeding season, 3 of 12 active nests fledged 7 chicks (2.3 chicks/successful nest). During 2014, 7 of 10 active nests fledged 22 chicks (3.1 chicks/successful nest); overall, 29 (2.9 chicks/successful nest) nestlings fledged in our study area. We used Program MARK to evaluate the influence of land cover on nest success. The top-ranked nest survival model for ferruginous hawks in ED was SNull (wi= 0.87) suggesting that none of the landscape predictor variables had any effect on survival and survival probability was constant between years; it also may suggest low sample size and an inability to detect an effect. Probability of nest survival during the study period in ED was 0.69 (95% CI = 0.61–0.83). In WD, the top-ranked nest survival model for ferruginous hawks was SSubstrate suggesting nest substrate had most influence on nest survival in WD; the probability of ground nest survival during the study was 0.77 (95% CI = 0.64–0.83) and the probability of tree nest survival during the study was 0.43 (95% CI = 0.28–0.56). We used logistic regression analysis to evaluate the influence of landscape variables on nest site selection. In ED, percent grass and percent pasture/hay was the top-ranked model for predicting nest site selection of ferruginous hawks and indicated positive association of nest-site selection with grasslands and pasture. In WD, percent grass and development was the top-ranked model indicating positive influence of grasslands and development on nest-site selection. . Top-ranked nest survival model for golden eagle was SNull (wi = 0.91) suggesting that none of the predictor variables had any effect on survival and survival was constant between years. Probability of golden eagle nest survival during the study period was 0.76 (95% CI = 0.58–0.81). We used logistic regression analysis to evaluate the influence of landscape variables on nest-site selection of golden eagles. Development was the top-ranked model (wi = 0.72) for predicting nest site selection of golden eagles and indicated negative association of nest-site selection with development. The model containing grass, pasture, and development ranked second and was competitive indicating positive association of active nests with higher percentages of grass and negative association with increase in development. The top-ranked nest survival model was SYear (wi = 0.65) suggesting survival was different between the 2013 and 2014 breeding seasons. S%Grass+%Water+Year model wi =0.23: ≤4 ΔAICc away) also was competitive indicating positive relationship of nests with %grass and % water in the landscape. Estimated nest survival for northern harriers in 2013 was 0.21 (95% CI = 0.22–0.55), and in 2014 was 0.49 (95% CI = 0.32–0.61). We used logistic regression analysis to evaluate the influence of landscape variables on nest-site selection. Grass, pasture, and water ranked as the top model for northern harrier (wi = 0.87). Logistic odds-ratio estimates from the top-ranked model for northern harrier indicated the odds of nest-site selection were 1.48 (95% CI = 1.27–1.58) times greater for every percent increase in grasslands, and 1.2 (95% CI = 1.06–1.31) times greater for every percent increase in water; logistic odds ratio for percent pasture indicated no effect at the 900-m scale (1.06, 95% CI = 0.98–1.14). Our results indicate major decline of nesting ferruginous hawks in agriculture dominated regions of the northern Great Plains where land-use change has modified open grassland and pastures into row crop agriculture in the last four decades. Our study also demonstrate close association of grassland, pastures and wetlands with nest-site selection of ferruginous hawks, golden eagles and northern harriers, and avoidance of ground based disturbance by all three raptor species. Our findings indicate a need to manage pasture, wetlands, and grasslands in areas suitable for nesting of ferruginous hawks, golden eagles, and northern harriers and control increased fragmentation to support all grassland nesting raptors in the northern Great Plains.
Includes bibliographical references
Number of Pages
South Dakota State University
Copyright © 2016 Shubham Datta
Datta, Shubham, "Raptors in Temperate Grasslands: Ecology of Ferruginous Hawk, Golden Eagle, and Northern Harrier in the Northern Great Plains" (2016). Electronic Theses and Dissertations. 1022.