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An Evaluation of Implant Transmitters for Telemetry Studies of Black Bears


Gary M. Koehler, P. Briggs Hall, Washington Department of Fish and Wildlife, 600 Capitol Way N., Olympia, WA 98501 USA, and Mary H. Norton, 41502 S.E. Reinig Rd., Snoqualmie, WA 98065 USA

In 1995 and 1996, we tested implant radio transmitters (Advanced Telemetry Systems, Inc., Isanti MN) for telemetry studies of 25 male and 23 female black bears (Ursus americanus) in Washington. The objectives were: (1) to equip bears with radio transmitters that bears would retain longer than the 17 month retention of break-away radio collars used during 1994 and 1995, (2) to obtain more reliable hunter harvest data than provided by collars which were sometimes destroyed or discarded to conceal identification and location of harvested bears, and (3) to equip bears with transmitters which would be acceptable to the viewing public. Implant procedures were conducted by veterinarians P.B.H and M.H.N. Surgery required approximately 30 min (range 20 to 55 min) during which time morphological data were recorded concurrently. Bears were anesthetized with Telezol (Fort Dodge Laboratories, Inc. Fort Dodge IA) in dosages of 5.1 mg/kg body weight for females (n = 11) captured in snares, 6.3 mg/kg for females (n = 4) captured by helicopter during April-June, and 10.2 mg/kg for females (n = 4) captured by helicopter during September-October. Dosages were 4.6 mg/kg for males (n = 11) captured by snares, 4.8 mg/kg for males (n = 4) captured by helicopter during April-June, and 7.5 mg/kg for males (n = 5) captured by helicopter during September-October. Implant transmitter-marked males (n = 4) were located on 24 to 31 occasions by fixed-wing aircraft from April-December 1995 and was similar to the 20 to 35 locations for males (n = 8) marked with transmitter collars during the same time period. During 1996, 19 implant transmitter marked-males were relocated 189 times (Mean of X = 10, range 2-27) compared to 21 females relocated 445 times (Mean of X = 21, range 5-37). Radio signals could be received by aerial telemetry from bears in dens at a distance of 1.5 km and 250 m above ground, a distance less than provided by transmitter collars. For bears equipped with a radio collar and an implant transmitter, ground telemetry indicates that the transmitter collar could be received up to 1.5 km distance whereas telemetry signal reception for the implant transmitter may be limited to <100 m. The surgical implant procedures did not require additional immobilization time for bears or additional drug as approximately 30 min is required to equip bears with transmitter collars and drug dosages required for surgery were similar for non-surgical procedures. No physical complications from surgery were documented in contrast to transmitter collars which may result in cutaneous abrasion and ulcerations. The larger home range for males (Mean of X = 59.2 km2) than for females (Mean of X = 14.9 km2) and the limited signal transmission range for implant transmitters resulted in fewer relocations for males (Mean of X = 10) than for females (Mean of X = 21), which can bias home range area comparisons and mortality documentation. Improved documentation of harvest mortality from implants versus collars was not substantiated; of 4 bears with implants that were harvested 2 bears were found by hunters to be equipped with implants and 2 bears were not known to have been equipped.


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