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Woodland Caribou Population Dynamics in Northeastern Alberta
Abstract
Studies of woodland caribou (Rangifer tarandus caribou) in the Birch Mountains of northeastern Alberta were conducted during January 1976-June 1978; 29 caribou were radio-collared and located 1,001 times from fixed-wing aircraft. A population survey combining fixed-wing, transect flights and helicopter tracking yielded a late-winter density of 1 caribou/24 km2 over 1,400 km2. Adult bulls concentrated on this area in winter; adjusted resident density was 1/32 km2. Bulls comprised 46% of animals older than calves. Calves made up 12% of the total fall and winter population. Yearlings comprised 14% of 35 captured caribou during 1976-77, but individuals born during 1972-74 comprised only 15%. Radio-collared cows calved from 7 May to 2 June. Calf survival was 42% in the 1st 2 months of life; annual survival of 27 radio-collared adults averaged 85%. Composition of caribou groups changed conspicuously throughout the year. Caribou group sizes were smallest in summer (x̄ = 1.2) and largest in late fall after the rut (x̄ = 5.4). Seasonal ranges and movement patterns varied greatly among individuals, but seemed traditional among adult bulls. The latter made "long-distance" movements (> 11 km) up to 5 times per year to distinct seasonal ranges. Most cows moved 2 and sometimes 3 times per year. Seasonal range sizes were similar for bulls and cows, but individual cows were more sedentary and their seasonal ranges overlapped more. Mean annual range size of adult bulls was 1,196 km2, and that of cows was 539 km2. Seasonal changes in relative use of habitat types seemed related to availability of food, snow depths, and social behavior. Most locations (69%) were in lowland cover, predominantly black spruce (Picea mariana) muskegs.
... For our density estimation models, we used camera trap data from 2018 to 2019 for Richardson and 2016 -2019 for Algar. We subset data to August 1 -October 31 of each year as this was when populations were most likely to be demographically closed between spring calving and the beginning of winter movement (Fuller and Keith 1981). Importantly, both sexes have antlers in the final stages of growth during this period in advance of rutting and mating, such that the number of antler points could be used for partial identity information. ...
... If SC models were combining individuals, estimates may reflect the abundance and density of groups. Caribou form temporary aggregations during the rutting period (Fuller and Keith 1981), and group sizes reached maximums of 7 and 4 in the Richardson and Algar study areas, respectively. Multiplying Algar SC estimates in 2018 by the average group size (1.5) would result in point estimates of D = 51 -60/1000 km 2 , which match previously estimated winter densities for the entire range (McFarlane et al., 2020). ...
... For example, extrapolating estimates of caribou density from the relatively small study areas in this study to other regions in order to match the larger spatial extents of fecal and aerial sampling would almost certainly overestimate density. Furthermore, caribou movements are typically greater in the rutting period (August-October), which we selected for density estimation due to the availability of antler point counts for SPIM estimation, than in the winter (December/January -March) when aerial and fecal surveys occur (Fuller and Keith 1981;McFarlane et al., 2020). Indeed, σ estimates in Algar were not always similar to previously estimated values for ESAR (Fig. 2). ...
Population monitoring is critical to wildlife conservation, but density estimation is difficult for wide-ranging, unmarked species inhabiting remote habitats. Furthermore, recent investigations into density estimation with camera trap data has revealed unmarked models to be potentially unreliable, prompting cautious application and continued model development. Two related approaches with increasing appeal include spatial count (SC), which infer latent identities from the spatial pattern of detections, and spatial partial identity models (SPIM), which additionally leverage partial identity covariates (e.g., sex, antler point count, and presence of GPS/radio collar). To assess the performance of unmarked density models, we applied SC and SPIM to camera trap data of threatened boreal caribou in Canada, which are declining but have few rigorous density estimates across their broad distribution to inform conservation efforts. In particular, we focused on two spatially proximate caribou ranges in northern Alberta, Canada that differ in estimated caribou demographic trends, disturbance histories, and abundances of caribou predators and apparent competitors. Estimates of caribou density varied over a 4 year period (2016 – 2019), and were higher in the region with more stable reported growth rates and less anthropogenic disturbance (mode SPIM estimates: 155 – 225/1000 km² vs. 19 – 96/1000 km²). However, density estimates differed by modeling approach and had low and variable precision, hindering inferences about population status and trajectories. Simulations suggest that SPIM estimates may have been less biased and more precise. SC models likely underestimated density by mistaking detections of neighboring individuals as recaptures of a single individual, although SPIM may also have overestimated density by inflating assignment probabilities of detections to non-existent individuals. Findings highlight the need to explore how grouping dynamics and non-independent movement violate assumptions and reduce the ability to distinguish individuals. We advocate continued investigation into the accuracy of unmarked density estimation approaches, the ecological and sampling conditions appropriate for different unmarked density models, and coordination across sampling efforts and analyses to improve population inferences.
... Assuming a calf:adult caribou ratio of roughly 1:2, we simulated calf numbers of 30, 65, or 100 calves in our simulations. Caribou calf mortality was highest within the first month or two of life (Fuller and Keith 1981, Stuart-Smith et al. 1997, Rettie and Messier 1998. For calves, we therefore simulated calf-wolf encounters for 31 d and refer to it as one "calving season." ...
... Given the maximum number of 8 wolf packs, maximum mortalities per year were 73% for caribou and 39% for calves in our default simulations (Table 5). Reported mortalities for adult caribou (7-22%, Fuller and Keith 1981, McLoughlin et al. 2003) were up to an order of magnitude lower. The calf mortalities in our findings were comparable to reported ranges (58% within the first two months after calving, Fuller and Keith 1981). ...
... Reported mortalities for adult caribou (7-22%, Fuller and Keith 1981, McLoughlin et al. 2003) were up to an order of magnitude lower. The calf mortalities in our findings were comparable to reported ranges (58% within the first two months after calving, Fuller and Keith 1981). In our simulations, absolute prey mortality ultimately was a product of encounter probability and wolf kill success given an encounter. ...
In Canada, boreal caribou (Rangifer tarandus caribou) are declining in numbers, in part due to increased predation by wolves (Canis lupus). One management option to reduce wolf–caribou interactions and thus protect caribou is to remove man‐made linear features (LFs), structures such as roads, trails, and cut lines, which are used by wolves as traveling paths. Linear features increase wolf traveling speed and could additionally facilitate wolf entry into caribou habitat. Our goal was to quantify the expected effect of LF removal on caribou mortality and investigate whether this LF restoration could be a sufficient measure to stop caribou declines. We simulated the effects of LF restoration on caribou adult and calf survival in spatially explicit wolf–caribou encounter models. The models were parameterized using Global Positioning System (GPS) data, hidden Markov models (HMMs), and information from the published literature. Complete LF restoration decreased wolf traveling speed and thus reduced caribou mortality. The proportional reduction in adult caribou mortality ranged from 10 to 25% of its original value, and the proportional reduction in calf mortality ranged from 8 to 23%, depending on caribou density, number of wolf packs, kill probability given an encounter, and detection distance of wolves for caribou. Building on the model output, we used empirical caribou data to calculate the effects of reduced mortalities on the finite rate of annual population change, λ. Assuming that 25% or less of calf mortality was wolf‐related, λ stayed below one, that is, populations kept declining, even with complete LF restoration. With 50% of calf mortality due to wolves, caribou populations stopped declining (λ≥1) if adult and calf mortality were reduced by at least 19 to 24%. However, these values were not achieved in a majority of the parameter combinations in our study, not even with complete LF restoration. Given that LF restoration as a single measure is unlikely to stop boreal caribou populations from declining, we used a case example to illustrate how LF restoration could make a small contribution in a portfolio of short‐term and long‐term management options to reduce wolf predation on caribou.
... • Alberta: r = -0.04 (Fuller and Keith 1981), r = -0.12 (Edmonds 1988), r = -0.08 (Stuart-Smith et al. 1997) • Saskatchewan: r =-0.05 (Rettie and Messier 1998) • Quebec: r = -0.09 ...
... The preference of wolves for caribou and other small ungulates over moose (Holleman and Stephenson 1981) means that caribou Recovery Strategy for Woodland Caribou (Forest-dwelling, Boreal population) in Ontario must avoid wolves, especially during calving (Bergerud and Page 1987). Caribou cows typically achieve this by spacing themselves away from each other and calving alone (Fuller and Keith 1981, Bergerud et al. 1984, Bergerud 1985, Brown and Theberge 1985, Edmonds 1988, Bergerud 1996, Rettie and Messier 1998. This reproductive strategy, as well as the tendency for caribou to abandon forests in early seral stages following fire (Schaefer and Pruitt 1991) or logging Messier 2000, Smith et al. 2000), underscore the need to examine and understand caribou response to disturbance in an exceptionally broad spatial context. ...
... There is growing recognition around plasticity on other migration characteristics (e.g., distance, timing, and duration) as a strategy to deal with a changing environment [15]. Migration distances range from < 15 km [18], especially common in mountainous species that exhibit short altitudinal movements [7,8,19], to > 1600 km, in species that inhabit low elevation plains and follow precipitation gradients and high quality vegetation [9,20,21]. Timing and duration in migration are also flexible as ungulates respond to interannual and spatial variation in green-up, snow melt and rainfall [9,10,22]. ...
Background
Migration is a widespread strategy among ungulates to cope with seasonality. Phenology, especially in seasonally snow-covered landscapes featuring “white waves” of snow accumulation and “green waves” of plant green-up, is a phenomenon that many migratory ungulates navigate. Guanacos ( Lama guanicoe ) are native camelids to South America and might be the last ungulate in South America that migrates. However, a detailed description of guanacos´ migratory attributes, including whether they surf or jump phenological waves is lacking.
Methods
We quantified the migratory movements of 21 adult guanacos over three years in Patagonia, Argentina. We analyzed annual movement patterns using net squared displacement (NSD) and home range overlap and quantified snow and vegetation phenology via remotely sensed products.
Results
We found that 74% of the individual guanacos exhibited altitudinal migrations. For migratory guanacos, we observed fidelity of migratory ranges and residence time, but flexibility around migration propensity, timing, and duration of migration. The scarce vegetation and arid conditions within our study area seemed to prevent guanacos from surfing green waves; instead, guanacos appeared to avoid white waves.
Conclusion
Our study shows that guanaco elevational migration is driven by a combination of vegetation availability and snow cover, reveals behavioral plasticity of their migration, and highlights the importance of snow phenology as a driver of ungulate migrations.
... Home ranges for sedentary woodland caribou have been reported to be larger in the fall and winter than in the spring and summer (Shoesmith and Storey 1997, Edmonds 1988, Stuart-Smith et al. 1990, Schaefer et al. 2000. In addition, some individual animals have been reported to used distinct parts of their home ranges during summer and winter, while in others have occupied highly overlapping seasonally parts within their home ranges (Fuller and Keith 1981, Darby and Pruitt 1984, Cumming and Beange 1987, Ouellet et al. 1996, Stuart-Smith et al. 1997, Poole et al. 1999, Schaefer et al. 2000, Metsaranta 2002. ...
Chapter 3 2004 Doctorate of Philosophy Zoology. Effects of Habitat Fragmentation on the Behaviour and Ecology of Woodland Caribou, Rangifer tarandus caribou, in Northwestern Ontario. Guelph University.
... Because of this susceptibility, parturient caribou have developed spacing strategies to alleviate losses (Bergerud 1988(Bergerud , 1996, thus influencing the spatial and temporal dispersion of calves as a prey resource. Sedentary caribou, which are typically found in forested environments, reduce their movements and spread out at calving time to remain inconspicuous (Bergerud 1988(Bergerud , 1996, giving birth in small wetlands (Fuller and Keith 1981;Brown et al. 1986) or on islands (Bergerud et al. 1990). Migratory caribou, which usually inhabit open environments (Bergerud 1988(Bergerud , 1996, limit their risk and exposure to predators by migrating above tree line, where they aggregate on calving grounds and give birth in synchrony (Dauphine and McClure 1974;Bergerud 1996). ...
... During May to September, group size has been reported as limited to two animals, which usually represented cow/ calf pairs (Metsuranta 2002), while during February -March, group size increased and was usually represented by "herds" ranging from 2 to 50 individuals. Mean group sizes varying from 2.8 to 11.4 individuals have been reported in the literature (Fuller and Keith 1981, Darby and Pruitt 1984, Brown et al. 1986, Cumming and Beange 1987, Wilson 2000. ...
The availability of extensive range "space" is thought to be an important habitat characteristic that allows caribou to avoid predation and this apparent anti-predator strategy of spatial segregation may be further compromised in the presence of disturbance, when caribou are unable to properly "space themselves" to avoid predation. The research in this study was conducted to quantify the spatial interactions of woodland caribou in areas of overlap within home ranges during two seasons: summer and winter and determine if disturbance altered the two behavioral strategies used by woodland caribou. Temporal interactions among caribou with overlapping or shared home ranges were assessed using a non-parametric procedure. In the northwest region of Ontario, the spatial segregation distance of female woodland caribou was approximately 10 km during both summer and winter. Variations within this distance were observed and ranged between 2.5 and 7.9 km for summer distances and 1.6 and 8.5 km for winter distances. In both summer and winter, the mean distances between female woodland caribou were found to decrease as disturbance increased. The results of this study suggest that disturbance influences the ability of female woodland caribou to increase separation distances during summer. In areas where disturbance was light and summer ranges more accessible, females interacted little. In areas, where summer ranges were limited, the opposite occurred and females showed increased interaction.
Reductions in gene flow due to anthropogenic habitat fragmentation are often associated with reduced genetic diversity and increased population structuring in wildlife populations. We assessed fine-scale population structure and barriers to gene flow in threatened boreal woodland caribou ( Rangifer tarandus caribou ) in one of their southernmost ranges that contains both actively managed and unmanaged forests. A total of 763 non-invasively collected fecal DNA samples were genotyped at 12 microsatellite loci. Genetic clustering algorithms failed to identify a biologically meaningful pattern of population substructure, consistent with the observed pattern of isolation by distance (IBD). Population graphs identified two sites at the southern range periphery as genetically isolated from the remainder of the range. At the range level, genetic differentiation among sampling locations was best predicted by a combination of wildfire disturbance and geographic distance. Overall, this study suggests that woodland caribou are weakly genetically differentiated across the Brightsand Range, with both isolation by distance and isolation by resistance contributing to variation in allele frequencies.
Background
Migration is a widespread strategy among ungulates to cope with seasonality. Phenology, especially on seasonally snow-covered landscapes featuring “white waves” of snow accumulation and “green waves” of plant green-up, is a phenomenon that many migratory ungulates navigate. Guanacos (Lama guanicoe) are native camelids to South America and are one of the last ungulates in South America that migrates. However, a detailed description of this species’ migratory attributes, including whether guanacos surf or jump phenological waves is lacking.
Methods
We quantified the migratory movements of 21 adult guanacos over three years in Patagonia, Argentina. We analyzed annual movement patterns using net squared displacement (NSD) and home range overlap and quantified snow and vegetation phenology via remotely sensed products.
Results
We found that 74% of the individual guanacos exhibited short altitudinal migration. Additionally, we observed fidelity of migratory ranges and residence time, but flexibility around migration propensity, timing and duration of migration. Interestingly, we found that the scarce vegetation and arid conditions within our study area prevented guanacos from surfing green waves; instead, guanacos appeared to avoid white waves.
Conclusions
Our study demonstrates that guanaco elevational migration is driven by a combination of vegetation availability and snow cover presence, reveals behavioral plasticity of their migration, and highlights the importance of snow phenology as a driver of ungulate migrations.
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