Many people have bird feeders out and get enjoyment out of seeing birds in their back yard during the winter months.
If you pay attention you will have noticed that birds are well covered with a thick layers of warm feathers with the exception of their legs and feet, yet somehow these naked, spindly little legs and feet don’t freeze.
Birds actually have a nifty heat exchange system in their legs called Rete Mirabile which helps them prevent freezing. They share this system with some other animals such as fish and some mammals such as sloth and lorises.
In bird feet the arteries run really close to the veins causing warm blood heading from the body to the legs to warm the cooler blood flowing back to the body. This system reduces heat loss and is further enhanced by the arteries which relocate from a position closer to the skin during the summer more to the center of the leg during the colder winter month.
Bird lower legs and feet don’t contain muscles (just tendons). This causes the legs and feet to need very little energy allowing for reduced blood supply.
When it is really cold however even this system needs a little help and you will see birds sitting down with their feet tugged up into the downy feathers on their chest/belly to prevent their feet from freezing.
During severe cold spells we often receive calls from people who think waterfowl are frozen to the ice which most often is simply a case of a waterbird sitting on the ice using its feathers to keep its feet warm. They are often reluctant to move because exposing their naked feet to the cold can cause them to freeze, much like our fingers and toes.
Many healthy birds, particularly waterfowl spent a lot of time preening ensuring their plumage is perfectly oiled. The oil is produced by their uropygial gland which is located at the base of their tail. The oil repels water making it that the birds don’t get wet, but it also prevents them from freezing to the ice.
Waterfowl who are not healthy and therefore have neglected their plumage will often appear wet. These are birds who need help right away. In those causes don’t hesitate to contact you local SPCA, Humane Society, Animal Control or Authorized Wildlife Custodian.
Some of the birds of prey have adapted by growing feathers further down their legs and sometimes even feet reducing the exposed skin portion of the leg. This of course also helps reduce heat loss.