Northern Prairie Wildlife Research Center
Jennifer C. Higgins, Maine Department of Inland Fisheries and Wildlife, Bangor ME 04401 USA, Michael R. Vaughan, U.S. Geological Survey, Biological Resources Division, Virginia Cooperative Fish and Wildlife Research Unit, Blacksburg VA 24061-0321 USA, Dennis Martin, Virginia Department of Game and Inland Fisheries, Verona VA 24482 USA, and Adam D. Vashon, Maine Department of Inland Fisheries and Wildlife, Greenville ME 04441 USA
Reliable data on survival rates, cause and timing of mortality, and relative importance of different mortality factors for black bear cubs are limited. Cub survival usually is estimated by comparing the mean litter size between cubs of the year and yearlings. Data from observations of cubs provide minimum survival estimates, and often the cause and timing of mortality are unknown. Radio telemetry studies may provide better estimates of cub survival, and can identify timing and cause of mortality. Our goal was to design a lightweight expandable radio collar that would compensate for one year of growth and would remain on a cub from its first denning period until its second denning period.
We designed two different expandable radio collars for black bear cubs, but used the same type of radio transmitter on both collar designs (Advanced Telemetry Systems (ATS), Isanti, MN). Each transmitter had a 12-month battery and a motion sensitive mortality mode that operated on a 4-hr delay. Transmitters weighed between 62 and 65.3 g and measured 55 mm x 25 mm x 15 mm. Both collar designs employed a sliding mechanism that allowed the collar to expand as a cub grew. The first collar, design A, was 37 mm wide and 410 mm long with the transmitter affixed to the center of the collar. The sliding mechanism consisted of a brass plate (150 mm x 30 mm) with a slit in the middle (143 mm x 4 mm) fitted on the collar and a 2-prong collar fastener fitted on the opposite end of the collar. The collar fastener was designed to slide along the brass plate, expanding the collar as the cub grew. The second collar, design B, was 460 mm long with the transmitter affixed to the center of the collar. On one side of the transmitter, the collar was 25 mm wide, on the other, it was 15 mm. We attached a 2-prong collar fastener to the 25 mm wide end of the collar, placed the narrow end of the collar between the 2 prongs of the collar fastener, and tightened the collar fastener enough to allow the collar to expand as the cub grew.
In 1995, we equipped 17 cubs in 8 litters (9M:8F) with an expandable collar (Design A). Six cubs in 4 litters wore their collars until their death (11-40 days, = 22.2 days), 4 cubs in 3 litters slipped their collars in the den (18-48 days, = 34.5 days), 6 cubs in 4 litters slipped their collars following den emergence (20-172 days, = 115.7 days), and one transmitter failed (20 days). A cub that slipped her collar was equipped with a collar in July, which she wore for 48 days.
In March 1996, we equipped 14 cubs in 8 litters (7M:7F) with an expandable collar (Design B). Four cubs were still equipped with radio collars as yearlings (327-353 days, = 333.8 days). In addition, a male cub, captured in a snare in August 1996, was equipped with a radio collar until March 23, 1997 (229 days). Three cubs in 3 litters were equipped with collars until their death (53-148 days, = 85.7 days), 2 cubs in 2 litters slipped their collars in the den (29-41 days, = 35.0 days), 2 cubs slipped their collars following den emergence (69-224 days, = 146.5 days), and 3 transmitters failed (203-281 days, = 235.7 days). None of the mortalities appeared to be related to the collar or their design.
Collar design A slipped off all cubs prematurely and provided data on cub survival only until late summer. Collar design B provided data on first year survival for 4 of 14 cubs and fewer cubs slipped their collars.