As I write (6 June), occasionally looking out into the garden for inspiration, a variety of birds are feeding on the seed we put out for them each day. Among the throng of ground-feeders are several chaffinches, male and female, together with several young. Nothing unusual in that, you might say, and you would be right – except
for the fact that two of the adult birds seemed to have collected some collected some
substance on their legs and feet.
Through the binoculars the mealy ‘socks’ look
like dried up, scaly porridge. Are these the same chaffinches Ann and I had seen
earlier in the year, I wondered, or have more chaffinches become afflicted? Until
a few months ago, when Ann contacted the BTO, I had no idea that what I am
viewing through the binoculars are viral papillomas or warts, a disease caused by
the Fringilla papilloma virus.
According to the BTO, who supplied the information,
the species susceptible are ‘chaffinches and, to a lesser extent, brambling.
In a large survey of birds captured for ringing in the Netherlands, papillomas
were found on 330 (1.3%) of some 25,000 chaffinches examined and both sexes
were affected. However, cases usually occur in clusters and quite high proportions
of local populations may be affected in outbreaks’. The ‘socked’ male I am
looking at in our garden, as I arrange my thoughts, has warty outgrowths on
both legs, while similar excrescences cover both feet of the affected female.
The growths are large, irregular-shaped and deeply fissured masses, which
almost engulf the entire lower leg or foot. The afflicted birds seem otherwise in
good health, although the female shows some lameness when she hops. The BTO
information sheet on this subject, states that the impact on welfare of afflicted
birds, even those with large papillomas, ‘may be little more than an inconvenience
and relatively minor irritation’. There are no known risks to humans or
domestic animals. However, ‘the fact that cases occur in clusters suggests that
the presence of affected birds presents a risk to others that are susceptible’.
‘The epidemiology of the disease has not been studied, but it seems unlikely
that it has an impact on population densities’.
Acknowledgement
I wish to thank the British Trust for Ornithology (BTO) for supplying the information sheet Warts: viral papillomas and allowing me to quote from it.
Colin Hawes
© 2003 Suffolk Naturalists' Society