Wisconsin’s ruffed grouse face several serious hurdles in maintaining stable populations, even in central and northern Wisconsin where generally stable but cycling populations are present.
This bird has a population cycle of about 10 years from peak to peak. West Nile Virus may have some impact on that cycle, although test results await. Now climate change may be throwing another curve at the state’s king of game birds, as it is often called by upland bird hunters.
Amy Shipley, a Ph.D. candidate from Ohio, settled at the UW-Madison Department of Forest and Wildlife Ecology to earn a degree by completing a thesis on how, or if, the bird may be hampered by climate change. Warmer temperatures cut into the snow pack typically experienced where this research is centered.
Ruffed grouse will snow-roost for protections from cold and possibly predators. Burrowing may describe the action better. The bird can be completely hidden by the snow, if deep enough, or be sitting in a bowl or depression.
Shipley’s degree adviser, Professor Ben Zuckerberg, obtained funding from several sources, to support Shipley’s research in the 9,000-acre Sandhill Wildlife Area in west-central Wisconsin. She trapped ruffed grouse for several years and studied how they coped with Wisconsin’s winters, comparing stress and survival of birds. Snow and cold weather usually exist, but less so than in the past.
Examining data from the first year of trapping revealed that as temperature got colder, the birds were more stressed, based on measuring a hormone extracted and measured from fresh bird droppings.
As the snow appeared and then became deeper, the birds were shown, again by hormone levels, to be less stressed.
At snow depths up to 15 to 20 centimeters, the hormone level was stable, but when it measured 20 centimeters and greater (about 8 inches), the birds were less stressed as determined by hormone levels.
In colder climates, birds are advantaged by snow greater than 20 centimeters. Snow is a great insulator and probably puts the bird at an advantage from predators, including mammals and avians.
Looking beyond Shipley’s initial analysis, assuming climate change is unlikely to reverse, could a shortage of snow and the advantages it provides be mimicked by, say, more of some type of vegetation cover?
Low limb-hanging conifers (evergreens) may provide some protection from cold and maybe predators. The evergreen limbs could also delay the loss of what snow falls, not making more snow but making snow last longer.
Even if stressed birds do survive this stress period, might that stress impact the spring reproductive period?
Jerry Davis can be reached at email@example.com.