Causes and Consequences of Broad-Scale Changes in the Distribution of Migratory Caribou (<i>Rangifer tarandus</i>) of Southern Hudson Bay

Abstract

ABSTRACT. Understanding the factors driving changes in species distributions is fundamental to conservation, but for wide-ranging species this is often complicated by the need for broad-scale observations across space and time. In the last three decades, the location of summer concentrations of migratory caribou (Rangifer tarandus) in southern Hudson Bay (SHB), Canada, has shifted south and east as much as 500 km. We used long-term data (1987 -2011) to test two hypotheses that could explain the distribution shift: forage depletion and anthropogenic disturbance. Over time and space, we compared the body size of live-captured adult female caribou, dietary quality from fecal nitrogen in July, the location of VHF-and GPS-collared female caribou in July, distribution of all-terrain vehicle (ATV) tracks and caribou tracks in August, and the proximity of collared caribou to sections of the coast with higher ATV activity in spring and summer. The forage depletion hypothesis was supported by greater body size and dietary quality in caribou of the eastern portion of SHB than in western SHB animals in 2009 -11. The anthropogenic disturbance hypothesis was supported by the negative correlation of the distributions of ATV tracks and caribou tracks on the coast in 2010 and the fact that caribou avoided areas with ATV activity by 10 -14 km. In 1987, collared caribou were observed largely along the coast in western SHB in mid-July, while in 2009 -11, they were inland in western SHB and along the coast in eastern SHB. While these locations demonstrate a substantial change in summer distribution over three decades, we were unable to differentiate between forage depletion and anthropogenic disturbance as a single causal factor of the distribution shift.Key words: anthropogenic disturbance; body size; diet; distribution; fecal nitrogen; forage; migratory caribou; Hudson Bay; Rangifer tarandus; range shift RÉSUMÉ. La compréhension des facteurs qui influencent les changements caractérisant les distributions des espèces est fondamentale aux efforts de conservation, mais pour les espèces dont l'aire de distribution est étendue, ce principe est souvent compliqué par la nécessité de faire des observations à grande échelle, dans le temps et dans l'espace. Au cours des trois dernières décennies, l'emplacement des concentrations estivales du caribou migrateur (Rangifer tarandus) dans le sud de la baie d'Hudson (SBH), au Canada, s'est déplacé vers le sud et vers l'est dans une mesure de 500 km. Nous nous sommes appuyés sur des données de longue haleine pour mettre à l'épreuve deux hypothèses susceptibles d'expliquer ce changement en matière de distribution, soit l'appauvrissement du fourrage et la perturbation anthropique. Au fil du temps et de l'espace, nous avons comparé la taille du corps des caribous femelles adultes capturées vivantes, la qualité de leur alimentation à partir de l'azote fécal en juillet, l'emplacement des femelles portant un collier de type VHF ou GPS en juillet, la répartition des traces de véhicules tout terrain (VT...

Heading for the hills? Evaluating spatial distribution of woodland caribou in response to a growing anthropogenic disturbance footprint

“…; Newton et al. ). The ability to move between areas in response to the availability of resources, predation risk, and dynamic environmental conditions can be viewed as an adaptation that allows caribou to persist in fire disturbed landscapes, reduce density‐dependent negative effects by using higher quality alternative ranges away from forage‐depleted areas, make use of seasonally available resources through migration, and reduce predation risk by spacing away from predators (Heard et al.…”

“…; Newton et al. ). High‐quality alternative ranges may no longer exist in landscapes disturbed by anthropogenic activities because of the number of forestry clear‐cuts, energy extraction infrastructure, and linear features such as roads, pipelines, and seismic lines (Kinley and Apps ; Tracz et al.…”

“…; Newton et al. ; Mahoney et al. ), boreal and mountain caribou exist in relatively small populations well below the carrying capacity of their range, where the effects of density dependence are likely to be weak and population size is believed to be regulated by top‐down effects (Seip ; Wittmer et al.…”

“…Declines in woodland caribou are believed to be a result of anthropogenic factors leading to habitat fragmentation and loss (Festa-Bianchet et al 2011;Hervieux et al 2013), while changes in spatial distribution of caribou (i.e., range shift) have been attributed to natural and anthropogenic factors (Schindler et al 2007;Newton et al 2015). The ability to move between areas in response to the availability of resources, predation risk, and dynamic environmental conditions can be viewed as an adaptation that allows caribou to persist in fire disturbed landscapes, reduce density-dependent negative effects by using higher quality alternative ranges away from forage-depleted areas, make use of seasonally available resources through migration, and reduce predation risk by spacing away from predators (Heard et al 1996;Briand et al 2009;McDevitt et al 2009;Newton et al 2015). High-quality alternative ranges may no longer exist in landscapes disturbed by anthropogenic activities because of the number of forestry clear-cuts, energy extraction infrastructure, and linear features such as roads, pipelines, and seismic lines (Kinley and Apps 2001;Tracz et al 2010).…”

“…Although density-dependent range shifts have been documented in migratory caribou herds after peaks in population size (e.g., Ferguson et al 1998;Newton et al 2015;Mahoney et al 2016), boreal and mountain caribou exist in relatively small populations well below the carrying capacity of their range, where the effects of density dependence are likely to be weak and population size is believed to be regulated by top-down effects (Seip 1992;Wittmer et al 2005;. Caribou distribution is also dependent on climate variability, and weather conditions can affect caribou behavior and the availability and quality of forage (Sharma et al 2009).…”