Climate change is expected to increasingly impact populations of woodland caribou and much focus has been placed on how a warming climate has facilitated the northward expansion of apparent competitors (e.g., white-tailed deer) and novel predators (e.g., coyotes). Climate change, however, may also exert effects on caribou populations that are not mediated by predation. Here, we used data from 21 populations in western Canada to assess the demographic response of woodland caribou to annual variation in a suite of meteorological and phenological metrics. Recent research on other ungulate populations suggests that climatic variation may have minimal direct impact on low-density populations such as woodland caribou because per-capita resources may remain sufficient even in “bad” years. We tested this prediction by relating climatic variation to juvenile recruitment and adult female survival, two vital rates with high influence on caribou demography. Contrary to the low-density/low-impact prediction, we recorded relatively strong effects in both rates, though explained variation across all demographic models was low, suggesting that factors other than adverse climatic conditions had a greater influence on caribou demography during our monitoring period (1994–2015). In general, juvenile recruitment was more affected by variation in growing season conditions in the year prior to birth, responding positively to longer, more productive growing seasons and negatively to those that were warmer and drier. Adult female survival, in contrast, was more affected by winter conditions, responding negatively to colder and more variable winters during the monitoring year and up to three years prior. Given these unexpected results, we discuss alternative explanations as to why these woodland caribou populations did not conform to the low-density/low-impact prediction. The demographic effects we recorded have direct implications for caribou conservation, highlighting the increased relevance of recovery actions when adverse climatic conditions are more likely to negatively affect caribou demography.
The Finnish wild forest reindeer Rangifer tarandus fennicus occurred throughout Finland still in the 17th century. It was gradually hunted to nationwide extinction by the 1920s but started to re-establish in the 1950s. Nowadays it occurs in Finland and the Western parts of Russia. The total world population is about 4000 individuals. The overall trend has been negative. In 2016, Finland and the EU started a seven-year conservation project WildForestReindeerLIFE. One of the actions is a new reintroduction into two areas in the subspecies’ historical range. This will be carried out through captive breeding and soft releases. Founders both from zoos and from the wild have been moved into two enclosures since autumn 2017. The first calves were born in May 2018. During the autumn 2019, we released 17 individuals of varying age and origin. Eight of them were born in the enclosures. Based on the GPS-tracking, camera traps and field observations, the released animals have mainly stayed close (< 1 km) to the enclosures. In one site, young males made two short-term explorative trips about 20 km distance from the enclosure. In the other site, adult zoo-born female with her calf explored the landscape for some days before settling down near the enclosure. Especially young zoo-born males have been tamer than expected. Near the breeding enclosures, their flight distance could be as short as a few meters, whereas away from the enclosure it appears to be longer. We’ll follow the behavior of released animals in the coming years.
Seasonality is an important component in shaping the dynamics that influence ecosystems, including mortality. We investigated temporal patterns of mortality in the boreal ecotype of woodland caribou (Rangifer tarandus caribou) in the southern Northwest Territories. Survival data were collected from 423 adult female caribou tracked by radio collars between 2003 and 2018, 172 of which died during the study from predation (106), non-predation (i.e., starvation), (15), harvest (11), accidents (3), or unknown causes (37). We used generalized additive mixed models to evaluate temporal patterns of mortality across the year. We found that probability of mortality followed a trimodal pattern with three peaks, one during pre-calving, one in mid-summer, and a smaller peak in late autumn, with a 6-fold difference in mortality risk between the lowest and highest periods of the year. Mortality risk was higher overall from late spring (pre-calving) to mid-summer than it was from late summer until the end of winter, despite decreasing for about 6 weeks post-calving. We explored potential factors contributing to mortality risk at different times of the year.
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