Post by yihunt on Jan 17, 2010 12:41:13 GMT -4
Ruffed grouse use deep, powdery snow to keep warm and elude predators -- human and otherwise
Sunday, January 17, 2010
By Ben Moyer
Jake Dingle/ PGCRuffed grouse hide so well that one can walk through a grouse woods without seeing a single bird.Grouse hunters have their own reasons for watching winter weather. Pennsylvania's late grouse season opened Dec. 26 and continues through Jan. 23. A little snow cover through that span can mean good hunting, when birds leave signs of their presence and when flushed grouse are easy to see against a background of white.
But from a hunter's perspective, northern and mountainous parts of Western Pennsylvania accumulated too much of a good thing when 40 or more inches of powder fell there during 2010's first two weeks.
Hunters found it exhausting to flounder through snow to their knees, and their dogs had it worse. Ruffed grouse, though, find the thick white mantle much to their liking. Deep, fluffy snow favors grouse winter survival in several ways.
Everywhere that ruffed grouse live, from Alaska to the mountains of southern Appalachia, they favor roosting inside the snowpack whenever it is deep enough and powdery enough to offer shelter. When snow lies at a minimum of about eight inches deep and lacks an icy crust, grouse dive into the powder from a perch on a limb or from headlong flight. Once inside the snowpack the birds may burrow ahead for several feet until they find a comfortable roost, completely hidden from the outside world, to spend the night.
Many winter hikers, and even hunters, unfamiliar with this habit have stood, mouth agape, as a grouse burst, snow flying and wings beating, up out of the snow seemingly out of nowhere.
"Snow-roosting is a two-part value for these birds. Primarily, it's a thermal advantage because powdery snow is such a good insulator," said Ian Gregg, a wildlife biologist with the Pennsylvania Game Commission. "When the air outside is cold, birds roosted under snow are well insulated, so they need to burn less energy and need to find less food than they otherwise would."
Research on snow-roosting has demonstrated that temperatures inside a grouse's snow burrow can remain at or near the freezing point, even when the air above drops below zero.
"The second advantage of snow roosting," Gregg said, "is that it offers protection from predators, particularly avian predators [hawks and owls] that research shows are the primary predators of grouse in our region. Under the snow, the birds are hidden from view and unavailable."
By roosting within snow, grouse not only shield themselves from the eyes of hawks and owls, the metabolic energy they conserve allows them to spend less time foraging, further reducing their exposure to attack.
When grouse must emerge to feed, they employ their specially adapted digestive system -- shared with related birds such as pheasants and quail -- that allows them to "fill up" fast and retreat to a roost. Winter grouse can quickly fill their crop, an elastic "sack" at the juncture of the neck and breast, with buds, twigs, or the fruit of wild grape or greenbriar, then grind the food in their muscular gizzard while roosting.
Gregg believes snow roosting is motivated by internal instinct, rather than a learned behavior.
"Grouse broods break up by early fall, or October at the latest," he said. "There is no interaction between the hen and her brood during the times of the year that grouse encounter snow, so that indicates an instinctive use of snow by the birds as a survival advantage."
South of Pennsylvania, ruffed grouse are never guaranteed sufficient snow for roosting. Still, the birds know its value and exploit it when they can.
"Appalachian grouse have been observed to snow roost whenever snow is present as opposed to potentially less advantageous tree roosts," wrote Virginia Polytechnic Institute's George B. Bumann in a doctoral thesis on the relationship of grouse roost selection to predation.
His research in Virginia, West Virginia, Pennsylvania and Rhode Island found what many grouse hunters with dogs may have already concluded: deep uncrusted snow also offers grouse protection from ground predators such as bobcats and foxes (and hunting dogs), presumably because the snow inhibits scent.
Snow, however, is not always a grouse ally. Bumann found that ice-crusted snow, in which grouse cannot roost, make them more vulnerable to predation than no snow at all. Bumann concluded that when grouse can't penetrate snow crusts, and must roost in trees, they are more visible against the white and easily seen by hawks and owls.
That may be a clue for human hunters as well. Warmer temperatures predicted this week are likely to reduce the snowpack and make it moister and more dense -- all less suitable for grouse roosting.
The hunting season's final week may be the best time this winter to bag a bird.
Sunday, January 17, 2010
By Ben Moyer
Jake Dingle/ PGCRuffed grouse hide so well that one can walk through a grouse woods without seeing a single bird.Grouse hunters have their own reasons for watching winter weather. Pennsylvania's late grouse season opened Dec. 26 and continues through Jan. 23. A little snow cover through that span can mean good hunting, when birds leave signs of their presence and when flushed grouse are easy to see against a background of white.
But from a hunter's perspective, northern and mountainous parts of Western Pennsylvania accumulated too much of a good thing when 40 or more inches of powder fell there during 2010's first two weeks.
Hunters found it exhausting to flounder through snow to their knees, and their dogs had it worse. Ruffed grouse, though, find the thick white mantle much to their liking. Deep, fluffy snow favors grouse winter survival in several ways.
Everywhere that ruffed grouse live, from Alaska to the mountains of southern Appalachia, they favor roosting inside the snowpack whenever it is deep enough and powdery enough to offer shelter. When snow lies at a minimum of about eight inches deep and lacks an icy crust, grouse dive into the powder from a perch on a limb or from headlong flight. Once inside the snowpack the birds may burrow ahead for several feet until they find a comfortable roost, completely hidden from the outside world, to spend the night.
Many winter hikers, and even hunters, unfamiliar with this habit have stood, mouth agape, as a grouse burst, snow flying and wings beating, up out of the snow seemingly out of nowhere.
"Snow-roosting is a two-part value for these birds. Primarily, it's a thermal advantage because powdery snow is such a good insulator," said Ian Gregg, a wildlife biologist with the Pennsylvania Game Commission. "When the air outside is cold, birds roosted under snow are well insulated, so they need to burn less energy and need to find less food than they otherwise would."
Research on snow-roosting has demonstrated that temperatures inside a grouse's snow burrow can remain at or near the freezing point, even when the air above drops below zero.
"The second advantage of snow roosting," Gregg said, "is that it offers protection from predators, particularly avian predators [hawks and owls] that research shows are the primary predators of grouse in our region. Under the snow, the birds are hidden from view and unavailable."
By roosting within snow, grouse not only shield themselves from the eyes of hawks and owls, the metabolic energy they conserve allows them to spend less time foraging, further reducing their exposure to attack.
When grouse must emerge to feed, they employ their specially adapted digestive system -- shared with related birds such as pheasants and quail -- that allows them to "fill up" fast and retreat to a roost. Winter grouse can quickly fill their crop, an elastic "sack" at the juncture of the neck and breast, with buds, twigs, or the fruit of wild grape or greenbriar, then grind the food in their muscular gizzard while roosting.
Gregg believes snow roosting is motivated by internal instinct, rather than a learned behavior.
"Grouse broods break up by early fall, or October at the latest," he said. "There is no interaction between the hen and her brood during the times of the year that grouse encounter snow, so that indicates an instinctive use of snow by the birds as a survival advantage."
South of Pennsylvania, ruffed grouse are never guaranteed sufficient snow for roosting. Still, the birds know its value and exploit it when they can.
"Appalachian grouse have been observed to snow roost whenever snow is present as opposed to potentially less advantageous tree roosts," wrote Virginia Polytechnic Institute's George B. Bumann in a doctoral thesis on the relationship of grouse roost selection to predation.
His research in Virginia, West Virginia, Pennsylvania and Rhode Island found what many grouse hunters with dogs may have already concluded: deep uncrusted snow also offers grouse protection from ground predators such as bobcats and foxes (and hunting dogs), presumably because the snow inhibits scent.
Snow, however, is not always a grouse ally. Bumann found that ice-crusted snow, in which grouse cannot roost, make them more vulnerable to predation than no snow at all. Bumann concluded that when grouse can't penetrate snow crusts, and must roost in trees, they are more visible against the white and easily seen by hawks and owls.
That may be a clue for human hunters as well. Warmer temperatures predicted this week are likely to reduce the snowpack and make it moister and more dense -- all less suitable for grouse roosting.
The hunting season's final week may be the best time this winter to bag a bird.