It’s been a busy week for mammal research! A publication out this week highlights the role of climate change in the expansion of white-tailed deer into the northern boreal forest. This research comes hot on the heels of a paper examining the effectiveness of recovery actions for southern mountain caribou. At the heart of both papers is the desire to identify how best to support caribou population recovery. Disentangling the effects of habitat and climate (in the case of deer) and of different recovery actions such as maternal penning (in the case of caribou) provides the evidence needed for informed decision-making around this threatened species. 

Read summaries of the research papers below, and join the researchers for one (or both!) of the webinars the week of May 13. 

Deer drift as the climate shifts: a warming climate helps deer invade the boreal forest

New research shows that the expansion of white-tailed deer into the northern boreal forest is linked to less severe winters

Over the past century, white-tailed deer have greatly expanded their range in North America. In the boreal forest of western Canada, habitat alteration—forestry and energy exploration creating more and new food sources—and a changing climate have enabled deer to push further north. However, what is good for deer is not necessarily good for other species, such as the threatened woodland caribou. 

The expansion of white-tailed deer into the boreal forest has been linked to caribou declines. White-tailed deer are disruptors; areas with more deer typically have more wolves, which predate on caribou, uprooting existing predator-prey dynamics. Understanding white-tailed deer populations is thus one piece of the caribou recovery puzzle. New research published in the journal Global Change Biology wanted to untangle potential factors behind deer expansion: is it human land-use, a warming climate, or both? 

The trick is that human land-use and climate are linked: as we move northward, the climate becomes more harsh and human land-use decreases, making it difficult to isolate these two factors. The northern Alberta-Saskatchewan border provided a convenient experimental set-up. While both sides have a consistent climate, habitat alteration is on average 3.6-fold higher on the Alberta side. Between 2017 and 2021, the research team maintained 300 wildlife cameras throughout the region to collect motion-triggered images of large mammals year-round. These images were used to estimate white-tailed deer density.  

Key findings from the study include:

• Deer density was significantly lower in areas with colder, snowier winters.

• Human land-use was associated with higher deer densities, but the effect was half that of climate and statistically insignificant.

Winter severity is expected to decline as climate change progresses. This means that deer are expected to keep expanding northwards and increase in abundance. When planning for caribou recovery, we need to keep these new forest residents in mind: the benefits of restoring habitat for caribou may be lessened by the sustained presence of deer and thus wolves on the landscape due to a warming climate.

Join a webinar on May 14 with lead author Melanie Dickie, Senior Caribou Ecologist, with the ABMI and Biodiversity Pathways, to learn more.  Register here: https://us02web.zoom.us/meeting/register/tZUkdOyqqDwtGNPomxg6q_MIUKcXik9ybPrB

Effectiveness of recovery actions for southern mountain caribou

A new paper in the journal Ecological Applications examines whether recovery actions used to increase southern mountain caribou populations in western Canada have been effective. 

Southern mountain caribou are the most imperiled of all woodland caribou. Over the last two decades, multiple southern mountain caribou populations have been extirpated and most that remain are small (<100 individuals) and rapidly declining. The ultimate cause of caribou decline is human-caused habitat loss and degradation, in turn leading to increased predation. As it can take decades to restore enough habitat for populations to recover, five types of recovery actions have been employed to avoid near-term caribou extirpation: maternal penning, supplemental feeding, translocation, reducing predator density, and reducing the density of alternate prey (e.g., moose).

Over thirty researchers from across British Columbia and Alberta came together to pool and analyze over fifty years of data on southern mountain caribou, using sources such as population estimates from aerial surveys and information on caribou mortality from collared animals. Data collection began for most populations after 1991, though the earliest data comes from 1973. Researchers found that while caribou have declined dramatically over the past few decades, including the extirpation of many caribou populations, there are roughly 50% or 1,500 more caribou on the landscape than if no recovery actions had been taken.

There is strong evidence that predator reductions have increased caribou populations and avoided further caribou extirpation events. This increase was seen under current levels of climate change and high levels of habitat loss. Actions such as maternal penning and supplemental feeding were most effective when coupled with predator reduction. Other actions such as prey reduction, wolf sterilization, or translocations had a lesser impact.

While recovery actions have stabilized or increased caribou abundance, the number of southern mountain caribou will remain dangerously low for years to come, with considerable risk of further extirpation events. Habitat protection and restoration are essential for long-term caribou recovery, but we cannot immediately regrow the mature forests that are naturally low in predators that caribou need to survive. If resource managers wish to maintain caribou populations on the landscape in the meantime, evidence-based, short-term recovery actions such as those studied in this paper would need to be considered.

Join lead author Dr. Clayton Lamb, Wildlife Scientist with Biodiversity Pathways, for a webinar on May 16. Register here: https://us02web.zoom.us/meeting/register/tZEpdO2vpz0oGtG9QOS_5Ef2vp7VU-7lQugO