Dekker D.,3819 112 A Street NW |
Drever M.C.,Environment Canada
Canadian Field-Naturalist | Year: 2015
Kleptoparasitism, or food piracy, is common in a wide range of taxa, particularly among predators, with the larger species forcing smaller species to surrender their catch. The Bald Eagle (Haliaeetus leucocephalus) is known to rob Peregrine Falcons (Falco peregrinus) of just-caught prey. We present time series of kleptoparasitic interactions between eagles and peregrines hunting Dunlin (Calidris alpina) that were wintering at Boundary Bay in the Fraser River valley, British Columbia. In 1108 hours of observation during January, intermittently between 1994 and 2014, we recorded 667 sightings of Peregrine Falcons, including 817 attacks on Dunlin resulting in 120 captures. The population of wintering Bald Eagles in the study area increased from about 200 in 1994 to 1800 in 2014, while the rate of kleptoparasitism at the expense of peregrines increased from 0.05 to 0.20. The increase in the number of Bald Eagles coincided with a decline in January sightings of Peregrine Falcons, which suggests that some falcons may have left the study area because of interference from eagles. The decrease in Peregrine Falcon numbers can be expected to have led to reduced predation risk for Dunlins. Christmas Bird Counts conducted in the Fraser River Valley have underscored the fluctuation in eagle and peregrine numbers reported here. © 2015 The Canadian Field-Naturalist.
Hedrick P.W.,Arizona State University |
Stahler D.R.,Yellowstone Center for Resources |
Dekker D.,3819 112 A Street NW
Journal of Heredity | Year: 2014
There is a striking color polymorphism for wolves in the Yellowstone National Park where approximately half the wolves are black. The genetic basis for this polymorphism is known, and fitnesses of the genotypes are estimated. These estimates suggest that there is strong heterozygote advantage but substantial asymmetry in the fitness differences of the 2 homozygotes. Theoretically, such fitnesses in a finite population are thought to reduce genetic variation at least as fast as if there were no selection at all. Because the color polymorphism has remained at about the same frequency for 17 years, about 4 generations, we investigated whether this was consistent with the theoretical predictions. Counter to this general expectation of loss, given the initial frequency of black wolves, the theoretical expectation in this case was found to be that the frequency would only decline slowly over time. For example, if the effective population size is 20, then the expected black allele frequency after 4 generations would be 0.191, somewhat less than the observed value of 0.237. However, nearly 30% of the time the expected frequency is 0.25 or greater, consistent with the contemporary observed frequency. In other words and in contrast to general theoretical predictions, because of the short period of time in evolutionary terms and the relatively weak selection at low frequencies, the observed variation and the predicted theoretical variation are not inconsistent. © 2014 The American Genetic Association 2014. All rights reserved.
Dekker D.,3819 112 A Street NW |
Out M.,Augustin Hanicottestraat 15 |
Tabak M.,704 3061 Kent Avenue N.E. |
Ydenberg R.,8888 University Drive
Condor | Year: 2012
Kleptoparasitism in birds has been the subject of much research, and the Bald Eagle (Haliaeetus leucocephalus) is a known kleptoparasite. It has been reported to pirate ducks captured by Peregrine Falcons (Falco peregrinus), but ours is the first study to examine the effect of kleptoparasitic Bald Eagles on the kill rate of shorebird-hunting Peregrines and indirectly on a population of Dunlins (Calidris alpina) wintering in coastal British Columbia. Bald Eagles increased seasonally and yearly from October 2008 to January 2011. When eagles were scarce, Peregrines hunted ducks as well as Dunlins. Conversely, when eagles were numerous Peregrines hunted Dunlins only. In 56 instances, one or more eagles closely followed hunting Peregrines and retrieved 13 Dunlins dropped or downed by the falcons. The Peregrines were also kleptoparasitized by Gyrfalcons (Falco rusticolus), which pirated 11 Dunlins from Peregrines. Observed losses to kleptoparasites amounted to 24 (36%) of 67 Peregrines' captures. The kill rate per hour of observation was 0.05 hr-1 in October and November when eagles and Gyrfalcons were few but significantly higher at 0.18 hr-1 during January and February. In January 2011, when intraguild kleptoparasites were most abundant, the Peregrine's kill rate was 0.30 hr-1. These results support the hypothesis that kleptoparasites had an indirect effect on a population of wintering Dunlins because Peregrines compensated for prey lost to kleptoparasites by increasing their kill rate. © The Cooper Ornithological Society 2012.
Dekker D.,3819 112 A Street NW |
Dekker I.,3819 112 A Street NW |
Christie D.,Albert County |
Ydenberg R.,Simon Fraser University
Waterbirds | Year: 2011
The interaction of aerial predators and migrant Semipalmated Sandpipers (Calidris pusilla) was studied at Mary's Point in the upper Bay of Fundy, New Brunswick, Canada, during August of 2009 and 2010. Peregrine Falcons (Falco peregrinus) were locally reintroduced and increased from one active nest site in 1989 to 27 in 2010, which coincided with a decline of sandpipers roosting at Mary's Point from an annual mean of 161,000 in 1976â€"1982 to 15,000 or less during this study. Mean roosting time of flocks was 33 min (range = 10 to 40 min; N = 6). Sandpipers returned to the beach 1 h:36 min after high-tide (range = 1 h:10 to 2 h:13 min; N = 5), but were soon flushed again by falcons. On ten of 19 days, during part of the high-tide period, flocks of sandpipers remained in flight over the ocean. Termed Over-Ocean Flocking (OOF), this behavior was seen on days when spring tides inundated all beach habitat, and also at lower tides, which supports the hypothesis that OOF is an antipredator strategy intended to avoid surprise attacks by falcons near the shore. Raptors sighted during 128 hours afield included 226 Peregrines, 20 Merlins (Falco columbarius) and two Sharp-shinned Hawks (Accipiter striatus). At 1.0â€"3.2 Peregrine sightings/h -1 (mean 1.8) the level of disturbance is high and supports the hypothesis that the decline in roosting sandpipers at Mary's Point is linked to predation danger.