Reddish Vale Country Park
All images, copyright, Stockport Nature.Com
Reddish Vale Country Park
How Birds Keep Warm
What To Feed Them In Winter
Birds have developed various ways to keep warm in the colder months, so that even the smallest species can survive the harshest winters.
An important factor for a bird surviving the cold weather is body temperature, birds have a higher metabolic rate than humans which means their body temperature is higher than ours, a birds temperature is around 105 Degrees Fahrenheit, the exact temperature varies in different species, and the temperature can change during the day depending on climate and various activities.
The most obvious ways birds keep warm is with their feathers, they have basically two types (some have more). Feathers are an efficient insulator keeping the body heat in, Vaned feathers cover the outside and provide and are oiled for water protection and extra insulation, down feathers under the vaned feathers trap warm air and provide insulation. Many birds grow extra feathers in the autumn to give more insulation during the winter.
The photo of the heron on the left shows the efficiency of the feathers to keep heat in, the photo was taken late morning, the heron still has frost on his back from the previous night.
All birds have fat reserves that give extra insulation, in the autumn they will feed more to build up their fat reserves for the winter.
Small birds cannot go long without food and do not have large fat reserves, a sparrow in winter will be in trouble if it doesn't eat for 15 hrs, ducks and geese can go much longer because of their large fat reserves.
The legs on most birds are featherless but they are covered in specialized scales that help reduce heat loss. Smaller birds control the amount of blood going into the legs, the small capillaries carrying warm blood to the legs close up in cold weather restricting the blood flow and reducing the amount of cold blood returning to the heart, in warm weather the cappilaries open up allowing more blood flow to the legs and feet helping the bird cool down.
Duck’s feet have capillaries with a lace-like structure that weave among one another. This creates a counter current heat exchange mechanism. Warm blood flows down the legs from the body and meets the colder blood coming back up and heat is exchanged in the close capillaries. The warm arterial blood exchanges heat with the cooled blood, preserving the core temperature of the foot so that the duck can still function in a normal way even in icy water.
Fluffing feathers traps a layer of warm air under the feathers as added insulation, squatting enables birds to cover their legs and feet to keep them warm, as does standing on one leg with the other tucked up into the body.
Birds often sleep with their feathers fluffed and their beak tucked into them, this allows them to breath in warm air from under the feathers rather than the cold surrounding air and warm air is exhaled back under the feathers.
In very extreme circumstances birds will shiver to keep warm, this is a very effective way to increase their metabolic rate and increase their body temperature, but burns a lot of calories, a shivering bird is usually in trouble.
At dusk birds will seek out the warmest, draft free spot to roost, smaller birds will group together to keep each other warm, 60 wrens have been recorded in one nest box huddled up to keep each other warm. At dusk a blue tit has been flying in, and going behind one of the outside lights at the Visitor Centre taking advantage of the heat from the light.
Some species of birds migrate to and from the United Kingdom to escape the winter weather and find food. Worldwide around 4000 species of birds migrate (40% of all birds) and about half the UK's species migrate. Many species migrate to the UK to escape the winter weather in Eastern Europe, a blackbird visiting your bird table in January could be from Eastern Europe. The distances birds travel during migration can vary from a few miles to many thousands of miles. Migration is a risky buisness, it is thought that up to 50% of migrating birds never make it back to their birth place.
Sadly, in addition to surviving storms and bad weather, exhaustion and other natural obstacles, migrating birds are increasingly face human threats. Habitat destruction that affects staging posts handicap their ability to re-fuel. These include draining wetlands, cutting down forests. Pollution of the sea, water and air also affects them. Migrating birds are also distracted and killed by lit-up skyscrapers, lighthouses and other unnatural man-made formations that mislead them. Many migrating birds are also hunted, for food, and for sport.
Four of Reddish Vale's marathon migrators
What To Feed Wild Birds In Winter
High calorie food is the most important factor to keep birds warm, and lots of it.
In winter, nuts, seeds, grain and fat are the favoured food for most birds, bread is not a good idea as it is not high enough in calories. Avoid putting bread out at nesting time, it can choke the chicks.
A seed mix with a good variety of seeds is best, look for mixes with sunflower, niger, millet, flaked maize and peanuts, mixes using whole peanuts should only be used in winter as peanuts can choke chicks at nesting time.
Fat from cooking is not good for birds, it can smear and get on the birds feathers, and depending on the meat used can have a high level of salt. Fat from cooking is a breeding ground for bacteria, so potentially bad for birds health.
Lard and beef suet are good for birds in winter, they are pure fat, and it is not as suitable for bacteria to breed on.
Polyunsaturated margarines or vegetable oils, are unsuitable for birds. Unlike humans, birds need high levels of saturated fat, such as raw suet and lard. They need the high energy content to keep warm in the worst of the winter weather, since their body reserves are quickly used up, particularly on cold winter nights. The soft fats can easily be smeared onto the feathers, destroying the waterproofing and insulating qualities.
Meaty tinned dog and cat food can be used, blackbirds like it when they can't get any earthworms. Tinned dog and cat food may attract your local cats, if this is likely to be a problem, it is best avoided.
Cooked rice, brown or white (without salt added) is beneficial and readily accepted by all species during severe winter weather. Uncooked rice may be eaten by birds such as pigeons and doves.
Porridge oats must never be cooked, since this makes them glutinous and could harden around a bird's beak. Uncooked porridge oats are readily taken by a number of bird species.
Never give milk to any bird. A bird's gut is not designed to digest milk and it can result in serious stomach upsets, or even death. Birds can, however, digest fermented dairy products such as cheese. Mild grated cheese can be a good way of attracting robins, wrens and dunnocks.
Give fresh coconut only, in the shell. Rinse out any residues of the sweet coconut water from the middle of the coconut before hanging it out to prevent the build-up of black mildew.
Desiccated coconut should never be used as it may swell once inside a bird and cause death.
If you do feed your garden birds in winter, make sure there is always food available, the birds will remember where the food is and if there is none there they will have to burn more energy searching for new sources of food, if food has gone stale or mouldy remove it.
Make sure there is always clean unfrozen water available near your feeders and bird tables in winter.