Western sandpipers have altered migration tactics as peregrine falcon populations have recovered.
The presence of top predators can affect prey behaviour, morphology and life history, and thereby can produce indirect population consequences greater and further reaching than direct depredation would have alone. Raptor species in the Americas are recovering since restrictions on the use of dichlorodiphenyltrichloroethane (DDT) and the implementation of conservation measures, in effect constituting a hemisphere-wide predator-reintroduction experiment, and profound effects on populations of their prey are to be expected. Here, we document changes in the behaviour of western sandpipers (Calidris mauri) at migratory stopover sites over two decades. Since 1985, migratory body mass and stopover durations of western sandpipers have fallen steadily at some stopovers in the Strait of Georgia, British Columbia. Comparisons between years, sites and seasons strongly implicate increasing danger from the recovery of peregrine falcons (Falco peregrinus) as a causal factor. A decade-long ongoing steep decline in sandpiper numbers censused on our study site is explained entirely by the shortening stopover duration, rather than fewer individuals using the site. Such behavioural changes are probably general among migratory shorebird species, and may be contributing to the widespread census declines reported in North America.
Centre for Wildlife Ecology and Behavioural Ecology Research Group, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada. ydenberg@sfu.ca
Ronald C
RC
Ydenberg
Robert W
RW
Butler
David B
DB
Lank
Barry D
BD
Smith
John
J
Ireland
D025041:Animal Migration; D000818:Animals; D001717:Birds / Q000502:physiology*; D001837:Body Weights and Measures; D001955:British Columbia; D005247:Feeding Behavior / Q000502:physiology*; D019370:Observation; D011157:Population Dynamics; D011235:Predatory Behavior; D020304:Raptors / Q000502:physiology; D013997:Time Factors