GPS satellite telemetry provides new insight into capercaillie Tetrao urogallus brood movements
Per Wegge, Mats H. Finne & Jørund Rolstad
Wegge, P., Finne, M.H. & Rolstad, J. 2007: GPS satellite telemetry provides new insight into capercaillie Tetrao urogallus brood movements. - Wildl. Biol. 13 (Suppl. 1): 87-94.
High mortality among chicks, due to fragmentation and changes in habitat caused by commercial forestry, is considered one of the main reasons for the general decline in capercaillie Tetrao urogallus in boreal forests. Using GPS satellite telemetry, we studied the movement patterns of young capercaillie broods: 1) to test if this new technology could be applied to gain more detailed insight into behaviour and habitat selection at a small spatial scale, and if so, 2) to compare the broods’ relative use of planted and older, naturally regenerated forests. Hens of four broods with chicks 2-7 days old were captured and fitted with 90-g backpacks containing GPS units and VHF transmitters. The GPS units were programmed to record positions every 15 minutes, the shortest interval possible. With a storage capacity of 450 positions, movements could be monitored for ca 4.5 days. In our study area (Varaldskogen) with moderate topography, the GPS technology performed quite well. A total of 1,277 positions were obtained (84% of potential maximum), of which 77% were within 20 m of the true position of the brood. The movement patterns of the four broods were quite similar, with a mean speed of 83.2 m ± 9.9 (SE) per hour during the 4.5-day tracking period. Broods moved almost continuously during the 24-hour cycle, presumably foraging, although their speed was slower at night. The two oldest broods whose initial age was seven days moved faster than the two younger broods whose initial age was two and three days, respectively. Strong autocorrelation among successive positions made us examine habitat selection using a binominal choice method for each brood separately. When broods were inside old 'natural' forest, they remained there instead of moving into plantations. When inside plantations, they did not discriminate between remaining there and moving into nearby old forest, but they tended to move faster in plantations than in old forest. Clearly, the new, cost-effective GPS telemetry offers new and better opportunities for studying small-scale brood movement. Very frequent and accurate positions can be obtained without either disturbing the birds or leaving scent marks that may attract predators.
Key words: boreal forest, brood habitat, capercaillie, GPS, habitat selection, tetraonids
Per Wegge & Mats H. Finne, Department of Ecology and Natural Resource Management, Norwegian University of Life Science, NO-1432 Ås, Norway - e-mail: firstname.lastname@example.org (Per Wegge); email@example.com (Mats H. Finne)
Jørund Rolstad, Norwegian Forest Research Institute, NO-1432 Ås, Norway - e-mail: firstname.lastname@example.org
Corresponding author: Per Wegge