Golden eagle Aquila chrysaetos in Xinjiang: Nest-site selection in different reproductive areas

The reports about the geographical distribution, reproductive ecology and population dynamics of the golden eagle Aquila chrysaetos were mostly descriptive in China, and lack quantified studies for the nest-site selection of this species. We carried out our investigations by direct observations in the northern Xinjiang during 2004–2011, attempting to reveal the main factors that affected on the nest-site selection and the differences of ecological variables of reproductive areas in the species (Mts. Tian Shan spurs and Mt. Kalamaili). We measured 38 nests totally belonging to the 16 home ranges. The average number of nests in each home range was 2.38 ± 0.41, and with no significant difference (P > 0.05) between different reproductive areas. In all cases golden eagles nested on cliffs (n = 38) in our study area. The average external diameter of nests was (198.4 ± 8.2) cm × (159.3 ± 14.2) cm (Mean ± SE, n = 9), and inner diameter was (91.1 ± 4.4) cm. The nest-site selection was extremely significant difference (P < 0.01) for the different reproductive areas, i.e. elevation, hill height, nest-site height, cliff height, gradient, the distance to water resource, and the distance to residential area. The distance from the cliff bottom and from the cliff top were significant difference (P < 0.05). However, the slope position, nest position, distance to unpaved and paved road were not significant difference (P > 0.05). In Mts. Tian Shan spurs, the elevation was obviously selective (χ2 = 13.99, df = 4, P < 0.01), and mainly nested in altitude of 1 932–2 197 m, where the main aspects were SW (36.4%, n = 22) or SE (31.8%), and the slope gradient was above 85°. In Mt. Kalamaili, also it was found the significant differences for elevations (χ2 = 11.44, df = 3, P < 0.01), the eagle mainly nested in altitude of 1 112–1 423 m, with aspects of NW (68.8%, n = 16), and the gradient was relatively flat. In reproductive areas, eagles nested in the mid-slope parts and higher slope position (92.1%, n = 38). Eagles nested far from the seriously disturbed places by human, especially roads, residential area, mineral mines, etc. The principal component method of the factor analysis indicated that there were four main factors affecting on the nest-site selection by golden eagle in Mts. Tian Shan spurs: human disturbance factor (eigenvalue is 4.800, Ratio of contribution is 34.28%), nest position factor (3.002%, 21.44%), prey factor (2.601%, 18.58%), and terrain factor (1.305%, 9.32%). In Mt. Kalamaili, there are five main factors as following: terrain factor (eigenvalue is 5.110, Ratio of contribution is 34.07%), nest position factor (3.747%, 24.98%), human disturbance factor (2.123%, 14.16%), prey factor (1.584%, 10.56%), and gradient factor (1.111%, 7.41%). To conclude, human disturbance and landscape are the two main factors affecting on the nest-site selection of the eagle. The nest-site selection is a result of trade-off among the human disturbance, landscape and prey amount. Eagles take corresponding strategy of nest-site selection for adaptation to the various environments, having different conditions for the eagle reproductive. So, we recommended the improvement of the habitat fitness for the increasing of the reproductive success of the golden eagle.