Population dynamics of reintroduced elk (Cervus elaphus) in eastern North America

Abstract

Studies that focus on identifying factors that influence reintroduction success have often taken an individual population approach; however, investigating multiple populations can provide additional insight. The overall objective of this research was to emphasize the value of using within- and among-population approaches to identifying factors that influence the population dynamics of a reintroduced species. Elk (Cervus elaphus), a species that was extirpated from eastern North America during the late 1800s, has been reintroduced to portions of its former range over the past century through several initiatives. Today, there are several established populations across eastern regions of the USA and Canada, for which extensive monitoring data are available, creating an opportunity to investigate reintroduction success. I aimed to use these data to identify factors associated with changes in the survival and population growth rates of 10 reintroduced elk populations across eastern North America. More specifically, I: (1) performed a literature review detailing the history of elk reintroduction in eastern North America over the past century, (2) identified factors associated with the variation in population growth rates (reintroduction success) for 10 reintroduced elk populations using an among-population approach, (3) identified and assessed how climate affected the population growth rates of 7 reintroduced elk populations, and (4) investigated direct causes of mortality (predation and train collisions) associated with a single elk population experiencing low population growth. Although the number of successful elk restoration attempts has increased over the past century, there has been substantial variation in population growth rates among reintroductions. Major iv causes of elk mortality in restored populations differed between the pre- to post-acclimation phases of reintroduction. Population growth rates were negatively related to the percentage of coniferous forest within elk population range, suggesting that expansive areas of coniferous forests in eastern North America may represent sub-optimal elk habitat. The Burwash elk population in Ontario had low growth rate compared to most other populations reintroduced into eastern North America. Predation and train collisions were the most important source of mortality for this population. The number of annual elk-train collisions, as well as their locations, were monitored and recorded over 14 years. Collision locations were highly sitespecific and were positively correlated to the proximity of bends in the railway. By relating the number of annual elk-train collisions to various climate factors, I found that collision rates were positively related to snow depth. By analyzing field camera data, I found that elk used the railway mostly during the fall and spring, when elk commonly travel to and from wintering grounds. However, by examining VHF telemetry locations, I determined that elk were closer to the railway in winter than in any other season. Railways likely are perceived by elk as easy travel corridors, especially in the winter, and deep snow might prevent escape from oncoming trains. Black bear (Ursus americanus) and wolves (Canis lupus) were the major predators of elk in the Burwash population. White-tailed deer (Odocoileus virginianus), elk (Cervus elaphus), and moose (Alces alces), were the ungulate prey species available to both predators. To determine if predators prefer one ungulate species over another, and to identify which predator species is likely to have a greater impact on elk survival, I investigated predator diets. To compare rates of v ungulate use by predators in relation to prey availability, I calculated the relative abundance of each ungulate species. I found that wolves used juvenile and adult elk as their primary ungulate prey in greater proportions in comparison to their availability. Bears on the other hand, tended to use all ungulate species in proportion to their availability. Climate is well known to affect ungulate population dynamics; however, several factors (e.g.: density, predator presence), can govern the response. Relating the annual growth rates of 7 elk populations to various climate factors I found that responses were population specific. Increased annual snow fall was associated with declines in population growth rates for 2 of the 7 populations assessed and only 1 population responded negatively to increased summer temperatures. Climate likely interacts with other environmental variables to influence fluctuations in annual population growth rates which warrants further investigation. The results of this research will contribute to informed planning of future elk reintroductions and should support development through improved management. In addition, this research highlights the importance of using within- and among- populations approaches to investigating factors that influence elk reintroduction success.