While Gray Wolves continue to make a strong comeback in Washington State, their presence can not help but have an impact on other animals, especially those that these large carnivores target as prey.
White-tailed deer and mule deer, two distinct species common to Washington, are among the favorite captures of wolves. The wolves will chase the deer for long distances, sometimes over 10 km, looking for a good meal. The way these two deer species respond to the threat of being pursued by wolves in the early years of this predator's return could shed light on the changes in their behavior and numbers.
To help answer this question, researchers from the University of Washington and other institutions have been monitoring the behavior and activity of wolves and deer in Washington for three years. They found that wolf-exposed mule deer, in particular, changed their behavior to spend more time away from roads, higher altitudes and more rocky landscapes.
"In any particular ecosystem, if a predator returns, the prey probably will not react in the same way," said lead author Aaron Wirsing, associate professor at the UW School of Environmental and Forest Sciences. "We show that wolves do not have a uniform effect on different species of deer."
Their results were published on December 11 in the journal Oecologia.
The wolves were completely wiped out in Washington at the beginning of the last century, but began returning to that state from Idaho, Montana, and Canada about ten years ago. The latest estimates now indicate about 200 packaged wolves in eastern Washington.
White-tailed deer and mule deer are important foods for gray wolves. Although they may look like an untrained eye, white-tailed deer and mule deer are very different animals: the mule deer is bigger, with big dark ears and a black-tailed tail . The white-tailed deer is a smaller animal with an undeniably long tail with a white underside that stands straight when one is alarmed.
In addition to their physical characteristics, the two species differ in the manner in which they escape predators. When hunted, mule deer "stot", a quick link with all four paws touching the ground at the same time. This approach allows them to negotiate all types of terrain and can give them an agility advantage over predators in rocky and rugged areas where it may be difficult to run.
In contrast, white-tailed deer are moving away from predators and relying on them to locate them early enough to try to distance them.
Keeping in mind these known escape tactics, the research team focused on the "flight behavior" of deer living in wolf return areas and in areas without wolves. The researchers chose four separate study areas, all located near the small town of Republic, in the state of Washington. The four areas are home to both deer species, but only two were occupied by known wolf bands at the time of the survey.
In partnership with the Colville Tribes and the US Forest Service, researchers installed wildlife surveillance cameras, captured and glued collars on wolves and deer, and monitored data on all collars over a period of three years. years, from 2013 to 2016. and a dedicated team of UW students always ready to step in when an animal gets into one of the pitfalls.
"This part of eastern Washington is really special," said lead author Justin Dellinger, who has completed the work as a PhD student at UW and is now working for the Department of fish and wildlife of California. "There is a great diversity of large mammals, including all native prey populations such as sheep, moose and deer, and now we are starting to see a full complement of native predators, such as wolves, here too. "
Overall, the researchers found that mule deer in gray wolf areas changed their behavior to avoid wolves, mainly by moving to higher and steeper altitudes, away from roads and steep terrain and rocky. Alternatively, white-tailed deer favoring sprinting and early detection as a means of escaping predators were more likely to remain true to their normal behavior in wolf areas, sprinting on open terrain, with good visibility , including along the roads.
"Mule deer facing the threat of wolves are really changing their home range, on a large scale," said Wirsing. "They seem to be distant from their wolves before the wolves return, usually higher where the terrain is less smooth and where wolves are less likely to hunt successfully."
These larger movements in mule deer may have an impact on hunting opportunities. Indeed, some hunters from eastern Washington have already reported seeing mule deer higher on ridges where it is less accessible than in the past, said Wirsing. The results suggest that white-tailed deer hunting will probably not change to the same degree with the presence of wolves.
In the long run, changes between mule deer in wolf areas could affect other parts of the ecosystem and possibly reduce the number of deer and vehicle collisions. These potential impacts are an enticing fodder for future studies, Wirsing added.
White-tailed deer shape the acoustic properties of their forest habitat
Justin A. Dellinger et al., Habitat use of sympatric prey suggests divergent anti-predator responses to recolonizing gray wolves, Oecologia (2018). DOI: 10.1007 / s00442-018-4323-z