BRANTA — A. Adam Smith
Movement, survival and dispersal patterns of Swedish willow grouse (Lagopus lagopus lagopus L.)
Institution: University of Oxford, U.K.
Supervisors: CM Perrins, T Willebrand
Details: DPhil 1997 (Completed)
Address: The Game Conservancy Trust, Drumochter Lodge, Dalwhinnie, Inverness-shire, PH19 1AF (Oct 2005) Email
Subject Keywords: survival, mortality, dispersal, hunting, predation
Species Keywords: Willow grouse Lagopus lagopus
Abstract
Previous studies have suggested that patterns of mortality and dispersal are highly variable between regional populations of willow grouse (Lagopus lagopus). If such differences exist at landscape scales, theories concerned with the spatial structure of populations suggests harvesting is likely to alter these patterns because hunting pressure is spatially heterogeneous. Radio-telemetry was used to study whether hunting can induce changes in the survival and dispersal patterns shown by willow grouse in a mountainous Swedish landscape.
This work has provided evidence that through seasonal changes in habitat, willow grouse populations in the central mountains of Sweden are linked by dispersal of birds into a patchy population structure. Movement of adults and juveniles appeared to be triggered by changes in the availability of food and cover mediated through seasonal snowfall. Adult grouse migrated between seasonal ranges and displayed strong philopatry to previously used areas. There was a between sex difference in natal dispersal distances, juvenile females moving further than any other population class. Differences in dispersal patterns were associated with female breeding success but not with indices of grouse population density on the natal or breeding area.
Only season, and hunting pressure, significantly explained variation in the risk of death. The principal cause of natural mortality was predation by raptors during autumn, with few deaths during the rest of the year. Hunting mortality was additive, and was not compensated for by improved survival later in the year or by improved fecundity the following spring. However, partial compensation must have occurred through immigration as population densities did not fall at the expected rate. Hunter presence did not influence the seasonal abundance of raptors and hunting activity did not cause grouse to move at greater rates than on unhunted areas or induce long distance movements.
Published Papers
Smith, A.A. 1996. Seasonal trends in observations of raptors in the central Swedish mountains. Ornis Svecica 6: 123-126.
Olsson, G, Willebrand, T. & Smith, A.A. 1996. The effect of hunting on willow grouse Lagopus lagopusmovements. Wildlife Biology 2: 11-15.
Smith, A.A. 1997. Dispersal and movements in a Swedish willow grouse Lagopus lagopus population. Wildlife Biology 3: 279.
Smith, A.A. & Willebrand, T. 1999. Mortality causes and survival rates of hunted and unhunted willow grouse.Journal of Wildlife Management 63:722-730.
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