Wednesday, August 10, 2011

Ruffed Grouse

On 9 August 2011, Erika rode our bikes along the Cannon Valley Bike Trail in Goodhue County.  About two miles west of Welsh Station, Erika suddenly stopped short and pointed into the woods.  "What is that?" she exclaimed.  I hopped off my bike, my camera ready. She discovered a Ruffed Grouse.  Although they are known from the counties along the Mississippi River, this grouse is the first I've seen south of Duluth.
This Ruffed Grouse proved to be exceedingly tame, as grouse often are, so I was able to photograph the bird from relatively close range.  Examining the photo above closely, I noticed that the tip of the upper mandible seems to be missing. This defect may have been from a natural injury, birth defect, or wound from an encounter with a shotgun blast.
Across most of their range across Canada and parts of the northern United States, Ruffed Grouse numbers fluctuate an a ten-year cycle.  According to Rusch et al. (2000), these cycles are caused by Snowshoe Hare cycles that affect predators such as Northern Goshawks and Great Horned Owls. When rabbit populations crash, the predators turn to grouse. When rabbits are not present, the starving predators also migrate out of Canada into the northern United States, where they feed on grouse (and other prey).  
Grouse cycles and the reasons for them are less apparent in southeastern Minnesota and in other southern parts of the Ruffed Grouse's range that lack the Snowshoe Hares. Researchers in Minnesota found no direct correlation between grouse populations and migrating raptors. Furtman, in The Minnesota Conservation Volunteer, reports that Ruffed Grouse depend on aspen buds for winter food. In years with many Tent Caterpillars, stressed aspens may produce less palatable buds. Ruffed Grouse switch to less abudant or less palatable food and consequently their populations decline.  Warm winters may also adversely affect grouse.  Without snow cover in which to burrow and keep warm, grouse may overeat scarce food sources. Without snow burrows, the grouse may be more visible to predators. Whatever the reasons for grouse cycles in Minnesota, the cycle is generally at its low point in mid-decade and at its high point in years at the end and beginning of the decade.

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