During one of this winter's single digit cold spells, I was asked, "How come the feet of Canada geese don't freeze when standing on the ice?" When spotting geese or ducks standing on frozen ponds, with temperatures near or below zero, one would believe that their feet had to be frozen solid.
Not long after I graduated from the Game Commission training school, we here in Bradford County had been enduring a bitter cold and snowy winter and on one such morning, I received a call from a man saying that a flock of Canada geese had landed on a pond three days before and had not as yet moved. He was sure that the birds were frozen to the ice.
Although I had never heard of this occurring, I thought that perhaps it was possible. So, I drove to the area where the pond was located. It was a bitter cold day, with the wind blowing and well over a foot of snow on the ground.
PHOTO COURTESY OF BILL BOWER
The feet of ducks and geese neither freeze nor become entrapped in the ice. The arteries and veins of their feet lie against each other, and the cold returning blood is warmed by the arterial blood, effecting a rapid replacement of lost heat.
Through my binoculars, I watched the geese on the pond. After about 10 minutes of watching the geese, not one had moved. Although I had stayed in the car, strong winds continually rocked the vehicle. I surely didn't want to leave the warm car and walk across the field to the pond; however, I decided it was the only way to make sure the geese were not frozen to the ice.
Although my snowshoes were in the car, I decided against wearing them, thinking that I only would have to go a short distance before the geese noticed me and became alarmed. Well, I was wrong.
I had to struggle through the deep snow all the way to the edge of the pond before the geese began to raise their heads. They still didn't fly. I was out on the ice before they started honking and took flight. I again struggled through the deep snow to return to my now cold vehicle.
On the way home, I thought about what I had just experienced and knew that I had learned another lesson about wildlife. The feet of Canada geese neither freeze to the ice nor become entrapped in the ice.
Birds have a greater resistance to cold than mammals. Heat losses from their bodies are not only diminished by a coat of feathers, which encircles and insulates them with confined air, but their lower legs and feet are tendinous and their bills, which are horn, give up little heat loss.
Ducks and geese have a remarkable adaptation that prevents their feet from freezing while standing on ice. The arteries and veins of their feet lie against each other, and the cold returning blood of the veins is warmed by the arterial blood, effecting a rapid replacement of lost heat.
Ducks, geese and many other birds have this counter-current heat exchange system between the arteries and veins in their legs. The warm blood of the arteries passes closely to the cold vein blood, warming while dropping in temperature as it does. This means that blood flowing through the legs and feet is relatively cool, keeping the feet supplied with just enough blood to provide the temperature difference between the feet and the ice. Heat loss is greatly reduced, keeping the feet considerably warmer than the ice on which the duck or goose is standing.
Scientists have measured a mallard's heat loss to be only 5 percent of its body heat through their feet, while the head and the body, which are relatively hot, lose 95 percent of heat.
A bird's legs are relatively free of soft tissue. The muscles that operate the foot are mostly located higher up the leg and connected to the bones of the feet, with long tendons.
There is less need for warm blood since there isn't much soft tissue in the lower legs and feet. Many birds have valves in their leg arteries that control blood flow. There is evidence that some birds can pulse blood to the foot every so often to make sure that the foot does not suffer frostbite.
In cold weather, I've often seen ducks and geese standing on one foot, with the other foot tucked up under insulating feathers. This is to warm that foot, which helps to protect tissue and reduce heat loss even further.
After checking books and online to see if anyone had ever found waterfowl entrapped in the ice, I only found one incident. For three days, a man watched a tame white duck that didn't move and appeared to be frozen in the ice of the pond.
He finally got some equipment and went out on to the ice to rescue the duck; however, he found it actually was sitting on open water. The heat loss from the duck's body kept the water from freezing.
Domestic ducks and geese sometimes can become stuck in the ice as lakes and ponds freeze around them. Many of them are bred for food and they are heavy-bodied birds that often have difficulty jumping out of the water onto the ice.
Bower retired after 34 years as a wildlife conservation officer for the state Game Commission. He has published several books about his experiences. Questions and comments may be sent to him at 153 Redington Ave., Troy PA 16947.