Birds

Birds belong to the class Aves. There are about 10,000 species worldwide, and about 621 species in Britain (as at Jan. 2020), some of them being occasional visitors / vagrants.

They are warm-blooded, with a high metabolic rate, so need to feed a lot. Their bones are lightweight having large air-filled cavities, connected to the respiratory system. When they inhale, 75% of the air bypasses the lungs and flows into an air sac, which is connected to the bones to supply them with air. When they exhale, some of the fresh air from the air sac enters the lungs, replacing the exhaled original air – meaning that the lungs are filled with fresh air on both inhalation and exhalation.

Birds have feathers, which aid flight and thermoregulation, and are used for display or camouflage in some species.

In Dernol, many species are year-round residents, but we also have several migratory species that are here only for the summer – including Swallows, Spotted Flycatchers and, in some years, Fieldfares. In the UK generally, some species’ migratory habits are gradually changing with climate change,  and some migratory species are likely to become year-round residents, as is also happening with some species of moths and butterflies.

The numbers of some species have declined due to a reduction in their winter food supplies, with there being fewer flowering plants in the fields for winter seed, and the more thorough early cutting of hedgerows removing the berries before the residents and over-wintering migrants have had chance to feed on them. The increasing popularity of feeding birds in the winter in our gardens may hopefully offset some of this.