−−− BY LINDA JENKINSON −−−
This autumn has been a bountiful season and, over the last few weeks, our resident birds have been grazing intensely with one purpose, to lay down excessive fat for the cold months ahead. Birds use different strategies to survive over the winter. One method is caching. When food is plentiful some birds, such as jay and coal tit, will store food for leaner times and you might have seen jays flying backwards and forwards from a food source to a caching site. The next time you see a coal tit at your feeders, try to see what it does with the seed it takes away. There might be a cache in your garden.
Another strategy is to flee from the breeding area to a warmer climate. Over the last couple of weeks there has been a surge of birds from Arctic and subarctic regions. Many of the larger winter visitors including wildfowl and waders will appear in wetland habitat while other smaller birds may visit our gardens. Redwing, fieldfare, brambling and waxwing are everyone’s target species to see on garden berry bushes but some winter visitors, species that are also classed as residents in the UK such as robin, woodpigeon, goldcrest, chaffinch, blackbird and mistle thrush, may go unnoticed.
As the season moves on, food becomes scarce, daylight hours are short and foraging time decreases. Each short day is followed by a long, cold night so it’s vital that a bird can minimise its fat loss while it is roosting. This process begins after the post breeding moult when a bird grows extra down feathers and filoplumes under its main body feathers. These extra feathers create more layers and provide more insulation, a bit like you changing your duvet from a 4.5 tog to a 13.5 tog. Birds can grow up to 10% more feathers in some cases. When the temperature drops, a bird will shiver to create heat from the muscles and the extra layers of feathers are fluffed out to trap the heated air around its body. A bird will also position its beak under its feathers to prevent heat loss and it can also hide one leg inside its belly feathers too. Bird’s legs are amazing. They have adapted a special type of vascular system to prevent hypothermia in extreme temperatures. The blood vessels running to and from each foot pass closely parallel to each other. The warm arterial blood supplying the foot heats the returning blood in the vein before it gets back into the body. This is called the counter-current heat exchange mechanism. By using this method, a bird is protected from frostbite and maintains a constant body temperature.
When food becomes scarce, a bird may not be able to gain enough weight to survive the following night. If a bird is struggling in this way, its feathers will appear fluffed out during the day and it may appear to be tame. This bird needs your help badly. If you can, place food nearby without disturbing it too much.
Keep your bird feeders filled with high energy food and check that the feeding ports are not clogged up after wet, windy weather. It’s also very helpful if you can provide water for your garden birds. All those layers of feathers need daily maintenance to keep a bird warm, so water is essential. Put out dishes of water and keep your pond ice free if possible.
Linda Jenkinson teaches people about birds in and around Leeds. For details of classes email firstname.lastname@example.org or call
07778 768719. Visit www.startbirding.co.uk or Start Birding on Facebook and Twitter