Effectiveness of population-based recovery actions for threatened southern mountain caribou.

Habitat loss is affecting many species, including the southern mountain caribou (Rangifer tarandus caribou) population in western North America. Over the last half century, this threatened caribou population's range and abundance have dramatically contracted. An integrated population model was used to analyze 51 years (1973-2023) of demographic data from 40 southern mountain caribou subpopulations to assess the effectiveness of population-based recovery actions at increasing population growth. Reducing potential limiting factors on threatened caribou populations offered a rare opportunity to identify the causes of decline and assess methods of recovery. Southern mountain caribou abundance declined by 51% between 1991 and 2023, and 37% of subpopulations were functionally extirpated. Wolf reduction was the only recovery action that consistently increased population growth when applied in isolation, and combinations of wolf reductions with maternal penning or supplemental feeding provided rapid growth but were applied to only four subpopulations. As of 2023, recovery actions have increased the abundance of southern mountain caribou by 52%, compared to a simulation with no interventions. When predation pressure was reduced, rapid population growth was observed, even under contemporary climate change and high levels of habitat loss. Unless predation is reduced, caribou subpopulations will continue to be extirpated well before habitat conservation and restoration can become effective.

Behavioural trade-offs in response to external stimuli: time allocation of an Arctic ungulate during varying intensities of harassment by parasitic flies.

1. Macroparasites may be a major factor shaping animal behaviour. Tundra ecosystems inhabited by caribou and reindeer (Rangifer tarandus) are known for large concentrations of ectoparasites including mosquitoes (Culicidae) and black flies (Simuliidae), as well as endoparasitic oestrid flies (Oestridae). 2. Increased intensity and duration of insect harassment because of climatic warming is hypothesized as a potential factor in recent declines of Rangifer across the circumpolar north. Although there is a well-observed relationship between insect harassment and caribou/reindeer behaviour, the influence of ecto- relative to endoparasitic species is unclear. Climatic changes may favour the activity patterns, distribution or abundance of certain insect species; thus, understanding differential effects on the behaviour of Rangifer is important. 3. We recorded caribou behaviour using group scan and focal sampling methods, while simultaneously trapping insects and recording weather conditions on the postcalving/summer range of the Bathurst barren-ground caribou herd in Northwest Territories and Nunavut, Canada, during 2007-2009. 4. We developed statistical model sets representing hypotheses about the effects of insects, weather, habitat/location, and date/time on caribou behaviour. We used multinomial logistic regression models to explore factors affecting the relative dominance of behaviour types within groups of caribou and fractional multinomial logistic regression models to determine factors influencing time allocation by individual caribou. We examined changes in feeding intensity using fractional logistic regression. 5. Relative dominance of insect avoidance behaviour within caribou groups and time allocation to insect avoidance by individual caribou increased when oestrid flies were present or black flies were active at moderate-high levels. Mosquito activity had relatively little effect on caribou behaviour. Time spent feeding was reduced by the greatest degree when all three insect types were present in combination. Feeding intensity was influenced to a greater extent by the accumulation of growing degree days over the course of the postcalving/summer season than by insect activity. Changes in Arctic systems that increase the activity/abundance of ecto- and endoparasites could have implications for the productivity of Rangifer populations.

Corrigendum to: State-dependent foraging by caribou with different nutritional requirements.

[This corrects the article DOI: 10.1093/jmammal/gyaa003.].

State-dependent foraging by caribou with different nutritional requirements.

Foraging by animals is hypothesized to be state-dependent, that is, varying with physiological condition of individuals. State often is defined by energy reserves, but state also can reflect differences in nutritional requirements (e.g., for reproduction, lactation, growth, etc.). Testing hypotheses about state-dependent foraging in ungulates is difficult because fine-scale data needed to evaluate these hypotheses generally are lacking. To evaluate whether foraging by caribou (Rangifer tarandus) was state-dependent, we compared bite and intake rates, travel rates, dietary quality, forage selection, daily foraging time, and foraging strategies of caribou with three levels of nutritional requirements (lactating adults, nonlactating adults, subadults 1-2 years old). Only daily foraging times and daily nutrient intakes differed among nutritional classes of caribou. Lactating caribou foraged longer per day than nonlactating caribou-a difference that was greatest at the highest rates of intake, but which persisted even when intake was below requirements. Further, at sites where caribou achieved high rates of intake, caribou in each nutritional class continued foraging even after satisfying daily nutritional requirements, which was consistent with a foraging strategy to maximize energy intake. Foraging time by caribou was partially state-dependent, highlighting the importance of accounting for physiological state in studies of animal behavior. Fine-scale foraging behaviors may influence larger-scale behavioral strategies, with potential implications for conservation and management.

Understanding predation risk and individual variation in risk avoidance for threatened boreal caribou.

Predation risk is a driver of species' distributions. Animals can increase risk avoidance in response to fluctuations in predation risk, but questions remain regarding individual variability and the capacity to respond to changes in spatial risk across human-altered landscapes. In northeast British Columbia, Canada, boreal caribou populations declined as roads and seismic lines have increased, which are theorized to increase gray wolf predation. Our goal was to model risk and to evaluate individual variability and the development of risk perception by examining individual risk avoidance in response to reproductive status and age. We used locations from collared caribou and wolves to identify landscape features associated with the risk of a potential wolf-caribou encounter and risk of being killed given an encounter. We built resource selection functions to estimate individual responses to risk. We used general linear regressions to evaluate individual risk and linear feature avoidance as a function of age and reproductive status (calf or no calf). Linear features increased the risk of encounter. Older caribou and caribou with calves demonstrated stronger avoidance of the risk of encounter and roads, but weaker avoidance in late summer to the risk of being killed relative to younger and calf-less individuals. Mechanisms explaining the inverse relationships between the risk of encounter and risk of being killed are uncertain, but it is conceivable that caribou learn to avoid the risk of encounter and roads. Responses by females with vulnerable calves to the risk of encounter and risk of being killed might be explained by a trade-off between these two risk types and a prioritization on the risk of encounter. Despite the capacity to alter their responses to risk, the global decline in Rangifer populations (caribou and wild reindeer) suggests these behaviors are insufficient to mitigate the impacts of anthropogenic disturbances.