The problems facing the chaffinch

Male chaffinch - Fringilla coelebs - by Allan Drewitt
Male chaffinch - Fringilla coelebs - by Allan Drewitt
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The arrival of the cold weather has seen an upturn in the numbers of birds visiting bird tables and hanging feeders across the county.

Increasing numbers of finches, many of whom will have arrived from Continental Europe, can be seen feeding alongside the resident house sparrows and local blue and great tits. In with these birds are chaffinches, a familiar enough species but one whose populations will have been swelled by birds that have been pushed across the English Channel by recent poor weather and declining food resources.

Some of the chaffinches visiting garden feeding stations are likely to show leg abnormalities, typically in the form of grey or white lumps or lesions. In the worst cases, these can make one or other leg and/or foot appear much bigger than the other. There are two main causes of leg lesions in British chaffinches and it is entirely possible for an individual bird to have lesions on the same leg that are the result of both causes. One of these is a virus, which can cause a skin disease known as papillomatosis. The virus is known from both chaffinch and the closely related brambling, a species of finch that is a winter visitor to Suffolk. Tiny mites, belonging to the family Sarcoptidae, are behind the other types of lesions that we see in finches. These mites are related to those that affect poultry and, occasionally, pet budgerigars. There are several colloquial names for these ‘diseases’, including ‘tassel foot’, ‘mange’ or ‘scaly foot’.

Affected individuals are normally bright and active, and seemingly unaffected by the disease. However, severe cases can produce lameness or open the bird up to infection, which may result in the loss of toes or even part of the leg. Unfortunately, there isn’t anything you can do to help birds that have the lesions. We know that some can make a full recovery, while for others the lesions main remain over long periods of time. Since the diseases are passed from one bird to another through contact, the best advice is to reduce the risk of disease transmission by following sensible hygiene recommendations. Some of the best advice around these can be found on the Garden Wildlife Health project website (www.gardenwildlifehealth.org).

The Garden Wildlife Health project is a partnership between researchers working at the Institute of Zoology, the BTO, the RSPB and Froglife. The partnership has developed a web-based system, which allows members of the public to report the presence of diseased 
wildlife in their gardens. In some instances, where for example a dead bird has been found at a garden feeding 
station, the system allows veterinary scientists working the project to request carcasses for post mortem 
examination. The results of this examination, including the cause of death, are then fed back to the person reporting it, while at the same time supporting research into wildlife disease at the national level.