John S. Waller

EFFECTS OF TRANSPORTATION INFRASTRUCTURE ON GRIZZLY BEARS IN NORTHWESTERN MONTANA

Abstract Highways and railroads have come under increasing scrutiny as potential agents of population and habitat fragmentation for many mammalian species, including grizzly bears (Ursus arctos). Using Global Positioning System (GPS) technology and aerial Very High Frequency (VHF) telemetry, we evaluated the nature and extent of trans-highway movements of 42 grizzly bears along the U.S. Highway 2 (US-2) corridor in northwest Montana, USA, 1998–2001, and we related them to highway and railroad traffic volumes and other corridor attributes. We employed highway and railroad traffic counters to continuously monitor traffic volumes. We found that 52% of the sampled population crossed highways at least once during the study but that crossing frequency was negatively exponentially related to highway traffic volume. We found that grizzly bears strongly avoided areas within 500 m of the highway and that highway crossing locations were clustered at a spatial scale of 1.5 km. Most highway crossings occurred at night when highway traffic volume was lowest but when railroad traffic was highest. Highway crossing locations were flatter, closer to cover in open habitat types, and within grassland or deciduous forest vegetation types. Nighttime traffic volumes were low, averaging about 10 vehicles/hr, allowing bears to cross. However, we project that US-2 may become a significant barrier to bear movement in ∼30 years if the observed trend of increasing traffic volume continues.

Spatial and Temporal Interaction of Male and Female Grizzly Bears in Northwestern Montana

Spatial requirements of grizzly bears (Ursus arctos horribilis) in Montana are poorly understood, yet habitat management is based on attributes of female home ranges. We evaluated home range size, overlap, and spatial/temporal use of overlap zones (OZ) of grizzly bears inhabiting the Swan Mountains of Montana. Annual home ranges of adult males were larger (x = 768 km 2 ), and adult female ranges smaller (x = 125 km 2 ), than those of subadults. Overlap in annual home ranges of adjacent female grizzly bears averaged 24% (37 km 2 ), varied from 0 to 94%, and was less when one or both females had young. Female home range overlap was greatest when one of both members of a pair were subadults. Male home range overlap with females averaged 19% for adult males and 30% for subadult males. Most simultaneous use of the OZ occurred during summer. We investigated both spatial and temporal interaction of grizzly bears having overlapping home ranges. Thirty-seven of 49 (76%) adjacent female pairs showed symmetrical and random spatial use of the OZ indicating lack of territoriality. In one of 49 (2%) cases, simultaneous use of the OZ exceeded solitary use. Temporal use of the OZ was random in 44 of 49 (90%) female interactions. Avoidance behavior within the OZ of home ranges was indicated for 1 of 2 pairs of sisters following dispersal from their mother. Most male/female pairs exhibited symmetrical and random use of the OZ. In 12 of 21 (57%) cases where the female home range was enclosed within a male range, the male exhibited spatial attraction to the female range. There was no evidence of spatial avoidance of the OZ for male pairs. Habitat availability in different portions of overlapping home ranges helped explain the observed patterns of spatial and temporal interaction among grizzly bears. The overlap zone of home ranges had higher proportional availability of avalanche chutes, rock/forb lands, and slabrock than home range areas outside the OZ. These home range and behavioral characteristics occurred at a female-dominated population density of 2-3 solitary grizzly bears/100 km 2 .

Understanding the Causes of Missed Global Positioning System Telemetry Fixes

The use of Global Positioning Systems (GPS) on wildlifetracking collars has increased with improved technology. These collars obtain more locations per animal and potentially eliminate temporal biases caused by nonrandom radiotelemetry schedules (Rodgers et al. 1996). They have reduced potential biases in analyses of habitat use resulting from animals moving into thicker cover in response to the presence of researchers. The GPS technology has also increased the spatial accuracy of locations so that, for most applications, the error in locations is lower than the error of most habitat maps (Rodgers et al. 1996, Rempel and Rodgers 1997). One remaining potential bias is due to missed fixes, which occur when the GPS unit on the collar fails to receive signals from 3 or more satellites and thus, cannot calculate and record a position estimate. Previous studies have documented that terrain (D’Eon et al. 2002, Frair et al. 2004) and vegetation (e.g., Rempel et al. 1995, Edenius 1997, D’Eon et al. 2002) can affect fix success. Other authors have documented temporal effects due to deciduous canopy development and leaf-drop (Moen et al. 1997, Dussault et al. 1999), a changing satellite constellation throughout the day (Moen et al. 1997), and diminished success rates as batteries weaken (Gau et al. 2004). Few published studies have directly assessed behavioral influences on fix success. Only moose (Moen et al. 1996) and deer (Bowman et al. 2000) have been observed during fix attempts. Both species had reduced fix success when animals were bedded. Researchers have used activity sensors on elk (Rumble et al. 2001) and moose (Moen et al. 2001) to determine that inactive animals had lower fix success. We found no studies that examined whether there were differences in fix success between individual animals of the same species or that incorporated animal characteristics with terrain and vegetative characteristics into analyses of fix success. As bears exhibit high individual heterogeneity in behavior and in fix success, we felt it was important to include variables representing behavior and look for potential explanations for any patterns between individual bears and fix success. Location error for successful fixes has a number of causes including: 1) poor satellite geometry, typically expressed as high values of position dilution of precision (PDOP); 2) satellite clock errors; 3) satellite ephemeris errors; 4) unmodeled atmospheric delays; 5) multipath signals, when the collar receives multiple signals reflected from water or other surfaces; 6) receiver internal noise; and 7) selective availability (SA; Wells 1986). Many of these errors can be removed through differential correction (Puterski et al. 1992). The primary source of location error before May 2000 was SA, a U.S. Department of Defense policy under which random clock errors were introduced to satellite transmissions and reduced GPS location accuracy to 100 m 95% of the time (Wells 1986) but which could be as high as 200 m (Puterski et al. 1992). Since SA was discontinued in May 2000, a growing number of researchers no longer employ differential correction. Differential correction can be a time-consuming process, but it is still the only easy way to reduce errors (Adrados et al. 2002). Janeau et al. (2001) and Adrados et al. (2002) compared errors preand post-SA removal in 2 types of collars (one brand with differential correction and one without), and D’eon et al. (2002) addressed the overall error in coordinates since SA was turned off (98.5 m 95% circular error probability [CEP] for 2-dimensional (2D) locations and 26.2 m 95% CEP for 3D locations), but we found no research that examined how much additional error would be removed if the same locations were differentially corrected. Our objective was to determine which of the multiple factors affecting fix success were most important in our study area. We compared the influence of satellite availability, terrain, vegetation, animal size, and animal movement rates on fix success using data from GPS-collared grizzly bears. We compared the best models from collars on bears with tests of fix success at stationary sites and with error rates from collars placed at random test sites. We also compared error rates for corrected and uncorrected coordinates relative to the true location of GPS collars at random test sites.

Grizzly bear habitat selection in the Swan Mountains, Montana

In the contiguous United States grizzly bears (Ursus arctos horribilis) are classified as a threatened species, thus resource managers have a continuing interest in how grizzly bears use available habitats. We examined the use of satellite derived cover types by 19 individual radiomarked grizzly bears over 8 years and developed a hierarchial preference classification. We found that avalanche chutes were used in higher proportions than available during all seasons, along with slab rock. Shrub fields and timber harvest units were selected relative to availability during the summer and fall. Forested areas were among the least selected cover types during all seasons. Clear patterns of elevational movement were identified and were similar among most bears.