Effects of satellite transmitters on survival in Snowy Owls Bubo scandiacus

The use of tracking devices to monitor birds is extensive, but the effects of such instruments on equipped individuals are still insufficiently taken into account. Here we evaluate potential effects of backpack-mounted satellite transmitters (platform terminal transmitters; PTTs) on survival of 28 Snowy Owls Bubo scandiacus. Six confirmed deaths were all probably related to natural and human-induced causes. Although PTT operational time was significantly shorter than expected lifetime of Snowy Owls, five owls were observed alive after transmissions ceased. Additionally four PTTs stopped due to low battery levels, indicating end of transmitter life and not owl mortality. We found no evidence of mortality caused by PTTs, but sample sizes are relatively low and detrimental effects on equipped Snowy Owls cannot be excluded. We recommend caution when instrumenting large owls.publishedVersionNivå

Effects of satellite transmitters on survival in Snowy Owls Bubo scandiacus

The use of tracking devices to monitor birds is extensive, but the effects of such instruments on equipped individuals are still insufficiently taken into account. Here we evaluate potential effects of backpack-mounted satellite transmitters (platform terminal transmitters; PTTs) on survival of 28 Snowy Owls Bubo scandiacus. Six confirmed deaths were all probably related to natural and human-induced causes. Although PTT operational time was significantly shorter than expected lifetime of Snowy Owls, five owls were observed alive after transmissions ceased. Additionally four PTTs stopped due to low battery levels, indicating end of transmitter life and not owl mortality. We found no evidence of mortality caused by PTTs, but sample sizes are relatively low and detrimental effects on equipped Snowy Owls cannot be excluded. We recommend caution when instrumenting large owls

Breeding Home Ranges of Migratory Turkey Vultures Near Their Northern Limit

We used Global Positioning System (GPS) satellite transmitters to estimate the breeding home ranges of Turkey Vultures (Cathartes aura) in Saskatchewan, Canada from 2005 to 2009. Breeding ranges calculated using 95% Minimum Convex Polygons (MCP) ranged from 47 to 953 km2 and averaged (± SD) 371 ± 340 km2. Fixed-kernel home ranges (95%) ranged from 49 to 1,992 km2 and averaged 648 ± 731 km2. These ranges include both the smallest and largest summer ranges reported for the species. Spatial variation in range size may have been due to differences in availability of food and the quality of the home ranges involved, amplified by the species\u27 extremely low-cost soaring flight. Adults used all-night perches in varying locations up to 38 km from their nest house while traveling substantial distances to available carcasses to obtain food for their young. Identifying home range sizes for Turkey Vultures is a first step toward understanding how the species is increasing and expanding its distribution in Saskatchewan and elsewhere in Canada

Winter Ranges of Migratory Turkey Vultures in Venezuela

We used four Global Positioning System (GPS) satellite transmitters to calculate the wintering ranges of migratory Turkey Vultures (Cathartes aura) that breed in Saskatchewan, Canada, and winter in Venezuela. Between 2007 and 2011, 95% fixed-kernel estimators of range size varied from 54 to 76 731 km2 with an average of 16 814 ± 28 606 km2 (SD), while those calculated with 95% Minimum Convex Polygons ranged from 22 to 46 778 km2 and averaged 9545 ± 17 356 km2. The smallest wintering range was comparable to previously reported range sizes, but our largest wintering range greatly exceeded anything yet recorded. Variation in winter range sizes may be attributed to resource availability, migration costs, and the absence of obligations associated with breeding. Each vulture had a “primary nocturnal roost” to which it returned frequently; each spent more hours (evenings, nights, and mornings) at and within 1 km of such roosts, than it did foraging during midday. Our results increased our understanding of the feeding and movement ecology of North American migratory Turkey Vultures overwintering in South America