Do Moose & Deer Help Birds?

While Elaine and I were walking through the wonderfully treed pathways of Griffith Woods in west Calgary this month, we saw a set of fresh moose tracks and a stretch of willow shrubs that had been freshly clipped and no doubt enjoyed by alces alces, or the magnificent moose. Nicknamed the “swamp donkey” by some, we welcome the view of a moose anytime and almost anywhere. As luck would have it this Saturday morning, a sizable, young bull moose was nearby and we were fortunate enough to shuffle the shutters on our cameras as “junior” enjoyed browsing on aspen branches. While wondering how aspen branches would taste, I started thinking: “Do moose and deer improve habitat for birds?” After all, we’d seen songbird nests in the willows across Alberta in many of our journeys. .
Fortunately, research exploring the impact of deer and moose on bird habitat has been available since the 1940s, and similar research has increased in the current century. Deer populations in North America have rapidly increased in the last century due in part to decreased hunting and the decline in the number of natural predators. Researchers have found that when members of the Cervidae family are overly abundant in number, they do in fact have strong negative effects on bird species who rely on forest under story vegetation, that is vegetation below six feet in height. In addition, selective browsing of tree saplings alters the future composition of the forest canopy, potentially impacting avian communities. Thirdly, edible invertebrates may be eliminated by defoliation, reducing the supply of available food for birds. It is also possible that eggs and nestlings will be consumed by deer, elk or moose, impacting bird populations. A warming climate with reduced snowfall, permits smaller cervids, like whitetail deer, to have a greater chance of surviving winters as well as move further north into Alberta’s boreal forests where many songbirds nest.
While on our walk, Elaine and I stopped to look at a beautiful bird nest, wonderfully built and supported by a trio of willow branches. Bird species that use willow stands to raise their next generation include our numerous warblers, specifically both the Yellow and Wilson’s, various flycatchers, vireos, American Goldfinches as well as Song Sparrows and Lincoln’s Sparrows. It’s hard to imagine that deer and moose could negatively impact bird populations. Key in research is the population density of moose and deer in any given area. Larger numbers increase competition for food and habitat, which in turn would impact nesting sites and food sources for birds. Researchers note that the Cervidae factor should be included as a reason for declining bird populations.
As we headed back to the parking lot at Griffith Woods Park, we recalled the moments we were privileged to share with our “Bullwinkle”. Earth’s natural systems are incredibly complex and the species interrelationships aren’t always obvious without close study.