Have you noticed a lack of greenfinches in the garden recently? A few years ago it would have been quite normal to overlook chaffinches and greenfinches as you were straining to get a really good glimpse of a goldfinch quietly lurking in the hedge. However over the last couple of years an infection has ripped through greenfinch numbers, reducing some local populations by as much as thirty percent! This has led to a summer in 2010 where I have seen more charms of goldfinches trilling overhead that flocks of their bigger cousins.


The infection that has caused the decline is a tiny single-celled parasite called Trichomonas gallinae. This is hardly a recent phenomenon either, as there are fossilised jawbones from Tyrannosaurus Rex which exhibit scaring caused by Trichomonas infection. However, it has not been recorded in British finch populations until very recently and its effect has been devastating.


The parasite lives in the mouth and crop of the bird and can be passed from one individual to the next through infected saliva. The infection of the parasite causes the lining of the mouth and throat to swell and this, in extreme cases, can lead to the bird not being able to eat and in extreme cases not being able to breath either! Safe to assume this is a particularly distressing disease for the bird, and the symptoms are rather upsetting to witness too. Infected birds in the early stages appear withdrawn, fluffed up and generally out of sorts, when the infection really takes hold the head and beak can appear wet and traces of food will be stuck around the beak. In extreme cases the beak can be forced open by the swelling, with the bird unable to close its mouth.


If you suspect birds in your garden might be carrying the parasite or exhibiting some of the symptoms you should act quickly to help minimise the spread. Firstly it is thought that the parasite spreads most quickly in high population densities, so stop feeding birds in the garden immediately. Wash all feeders and bird baths in warm soapy water and dry thoroughly. After about a week you can resume feeding if you have not seen an infected bird, but start with small amounts and build up gradually over a period of several weeks in case there are infected birds nearby which might return and cross-infect other healthy birds. If this happens, return to the beginning of this process and start again, giving a little more time before resuming feeding.


If you do experience an outbreak in your garden, it would be a good idea to warn neighbours of the disease and adivse them to thoroughly clean feeding equipment if they regularly feed birds. Go easy though, as people can sometimes take badly to being told to do something out of the blue – so if it helps, take this article along and blame me!


It’s a serious disease, which is why I am penning this article, but the remedy is simple, if a little convoluted. If there’s something we can all do to put a halt to the freefall which greenfinch populations are suffering, then I for one want to be told about it!


Data collected to prove this collapse in numbers was gathered, not by scientists, but by birdwatching volunteers who kept records of bird numbers in their garden as part of a survey conducted by the British Trust for Ornithology. This reinforces the need for all of us to take more than just a passing interest in our local wildlife. Just because an animal is familiar and we are somewhat blasé about its place in our garden ecology, doesn’t mean that something isn’t lurking around the corner ready to decimate its numbers, like this latest worrying outbreak.


Its human nature to make sweeping generalizations (just like that one), a favourite will always be weather related; “it’s much wetter this summer” or “we haven’t had a proper winter since I was a boy”. But it’s only by keeping track of things that one can say categorically, there are less of such-and-such this year than so-many years ago. Statistics are vital, even if they are written in biro on the back of a cornflake box; If that cornflake box is from the 1970s and depicts the long-term demise of the house sparrow, it could be the most valuable dataset in ornithology!