Modelling broad‐scale wolverine occupancy in a remote boreal region using multi‐year aerial survey data

Abstract

Aim:We used data from aerial surveys of wolverine tracks collected in seven winters over a 10-year period (2003-2012) within a 574,287 km 2 study area to evaluate the broad-scale pattern of wolverine occurrence across a remote northern boreal forest region, identifying areas of high and low occupancy.Location: Northern Ontario, Canada.Taxon: Wolverine (Gulo gulo Linnaeus, 1758). Methods:We collected wolverine tracks and observations in 100-km 2 hexagonal survey units, making a total of 6,664 visits to 3,039 units, visiting each 1-9 times.We used hierarchical Bayesian occupancy modelling to model wolverine occurrence, and included covariates with the potential to affect detection and/or occupancy probability of wolverines.Results: we detected wolverines on 946 visits, 14.2% of total visits. Probability of detecting a wolverine varied among years and between the two ecozones in the study area. Wolverine occupancy was negatively related to two important covariates, the geographical coordinate Easting and thawing degree-days. A site occupancy probability map indicated that wolverine occupancy probabilities were highest, and standard error lowest, in the western and northern portions of the study area. Main conclusions:The occupancy framework enabled us to use observation data from tracks of this elusive, wide-ranging carnivore over a vast, remote area while explicitly considering detectability and spatial autocorrelation, yielding a map of probable wolverine distribution in northern Ontario that would not be possible using other methods of detection across a large region. With resource development pressures increasing in this globally significant region in the face of a changing climate, it is important to monitor changes in distribution of species like wolverines that have low population growth rates, large spatial requirements and sensitivity to human disturbance. This study demonstrates a relatively cost-effective and noninvasive alternative to monitoring based on wolverine harvest records, which have not been available since 2009 in Ontario due to changes in the provincial regulatory regime for this threatened species.

Abiotic stress and biotic factors mediate range dynamics on opposing edges

“…For example, snow had a strong positive effect on lynx and marten occupancy along their warm limits. These results are consistent with other studies (Hostetter et al, 2020; Hoving et al, 2005; Jensen & Humphries, 2019; Ray et al, 2018). However, there was also evidence of an indirect effect for lynx; snow depth‐mediated occupancy of coyotes and bobcats, its primary competitors that had a negative effect on lynx occupancy.…”

Wolverine Occupancy, Spatial Distribution, and Monitoring Design

“…Moreover, occupancy models fit in a Bayesian framework provide a straightforward approach to estimating the probability of occurrence of a species within subsets of the entire study area. Occupancy modeling has been applied to wolverine populations in Canada and Alaska (Magoun et al 2007, Gardner et al 2010, Whittington et al 2015, Ray et al 2018).…”

Wolverine density, survival, and population trends in the Canadian boreal forest

“…We would likely find evidence for heterogeneous wolverine density if we enlarged our study area and incorporated more variable habitat quality. For example, wolverine occupancy in Ontario decreases from northern to southern latitudes potentially because of a poorer climate and increased human development in the south (Bowman et al 2010, Ray et al 2018. Understanding variation in wolverine density over a larger space would further assist with population status assessments; however, it is unlikely that in most regions there will be surveys across a large enough space and at reasonable temporal intervals to provide reliable population numbers at the F I G U R E 4 Survivorship curves for population projections (2023−2042) in Red Lake, Ontario, Canada and Rainbow Lake, Alberta, Canada.…”

“…The species occurred throughout most of Ontario prior to the twentieth century but receded to the northwest portion of the province by the mid‐twentieth century (Petersen 1997, Dawson 2000). Wolverines have since expanded into much of northern Ontario (above 51° N latitude) although their stronghold appears to be the northcentral and northwestern portions of the province (Ray et al 2018). Licensed fur trapping is prohibited for those without treaty rights, but an unknown number of wolverines are incidentally harvested each year (Dawson et al 2010, Ray et al 2018).…”

“…Wolverines have since expanded into much of northern Ontario (above 51° N latitude) although their stronghold appears to be the northcentral and northwestern portions of the province (Ray et al 2018). Licensed fur trapping is prohibited for those without treaty rights, but an unknown number of wolverines are incidentally harvested each year (Dawson et al 2010, Ray et al 2018). Red Lake has forestry and mining activity and is on the southern edge of the current wolverine range in Ontario (Bowman et al 2010, Ray et al 2018) and the southern and eastern edge of wolverine distribution in North America (Figure 1; COSEWIC 2014).…”