Prey have evolved anti-predator defences that reduce or eliminate the risk of predation. Predators often reproduce at specific sites over many years causing permanent threats to local prey species. Such prey may respo...Prey have evolved anti-predator defences that reduce or eliminate the risk of predation. Predators often reproduce at specific sites over many years causing permanent threats to local prey species. Such prey may respond by moving elsewhere thereby reducing local population abundance, or they may stay put and adjust their behavior to the presence of predators. We tested these predictions by analyzing population abundance and anti-predator behavior within 100 m of and 500 m away from nests of sparrowhawks Accipiter nisus and goshawks A. gentilis for 80 species of birds. Population abundance of prey was reduced by 11% near goshawk nests and by 15% near sparrowhawk nests when compared with nearby control sites in similar habitats. Flight initiation distance （FID） of prey, estimated as the distance at which birds took flight when approached by a human, increased by 50% in the presence of hawk nests, providing evidence of adjustment of anti-predator behavior to prevailing risks of predation. Susceptibility to predation was estimated as log transformed abundance of the observed number of prey items obtained from prey remains collected around nests minus log transformed expected number of prey according to point counts of breeding birds. FID increased from 10 to 46 m with increasing susceptibility of prey species to predation by the goshawk and from 12 to 15 m with increasing susceptibility of prey species to predation by the sparrowhawk. These findings suggest that prey adjust their distribution and anti-predator behavior to the risk of predation.展开更多
We developed a habitat suitability model for predicting nest locations of breeding Northern Goshawks (Accipiter gentilis) in the high-elevation mixed forest and shrub-steppe habitat of south-central Idaho, USA. We use...We developed a habitat suitability model for predicting nest locations of breeding Northern Goshawks (Accipiter gentilis) in the high-elevation mixed forest and shrub-steppe habitat of south-central Idaho, USA. We used elevation, slope, aspect, ruggedness, distance-to-water, canopy cover, and individual bands of Landsat imagery as predictors for known nest locations with logistic regression. We found goshawks prefer to nest in gently-sloping, east-facing, non-rugged areas of dense aspen and lodgepole pine forests with low reflectance in green (0.53 - 0.61 μm) wavelengths during the breeding season. We used the model results to classify our 43,169 hectare study area into nesting suitability categories: well suited (8.8%), marginally suited (5.1%), and poorly suited (86.1%). We evaluated our model’s performance by comparing the modeled results to a set of GPS locations of known nests (n = 15) that were not used to develop the model. Observed nest locations matched model results 93.3% of the time for well suited habitat and fell within poorly suited areas only 6.7% of the time. Our method improves on goshawk nesting models developed previously by others and may be applicable for surveying goshawks in adjacent mountain ranges across the northern Great Basin.展开更多
文摘Prey have evolved anti-predator defences that reduce or eliminate the risk of predation. Predators often reproduce at specific sites over many years causing permanent threats to local prey species. Such prey may respond by moving elsewhere thereby reducing local population abundance, or they may stay put and adjust their behavior to the presence of predators. We tested these predictions by analyzing population abundance and anti-predator behavior within 100 m of and 500 m away from nests of sparrowhawks Accipiter nisus and goshawks A. gentilis for 80 species of birds. Population abundance of prey was reduced by 11% near goshawk nests and by 15% near sparrowhawk nests when compared with nearby control sites in similar habitats. Flight initiation distance （FID） of prey, estimated as the distance at which birds took flight when approached by a human, increased by 50% in the presence of hawk nests, providing evidence of adjustment of anti-predator behavior to prevailing risks of predation. Susceptibility to predation was estimated as log transformed abundance of the observed number of prey items obtained from prey remains collected around nests minus log transformed expected number of prey according to point counts of breeding birds. FID increased from 10 to 46 m with increasing susceptibility of prey species to predation by the goshawk and from 12 to 15 m with increasing susceptibility of prey species to predation by the sparrowhawk. These findings suggest that prey adjust their distribution and anti-predator behavior to the risk of predation.
文摘We developed a habitat suitability model for predicting nest locations of breeding Northern Goshawks (Accipiter gentilis) in the high-elevation mixed forest and shrub-steppe habitat of south-central Idaho, USA. We used elevation, slope, aspect, ruggedness, distance-to-water, canopy cover, and individual bands of Landsat imagery as predictors for known nest locations with logistic regression. We found goshawks prefer to nest in gently-sloping, east-facing, non-rugged areas of dense aspen and lodgepole pine forests with low reflectance in green (0.53 - 0.61 μm) wavelengths during the breeding season. We used the model results to classify our 43,169 hectare study area into nesting suitability categories: well suited (8.8%), marginally suited (5.1%), and poorly suited (86.1%). We evaluated our model’s performance by comparing the modeled results to a set of GPS locations of known nests (n = 15) that were not used to develop the model. Observed nest locations matched model results 93.3% of the time for well suited habitat and fell within poorly suited areas only 6.7% of the time. Our method improves on goshawk nesting models developed previously by others and may be applicable for surveying goshawks in adjacent mountain ranges across the northern Great Basin.
