We’ve been getting some very large numbers of finches visiting our garden feeders over the past few weeks, and numbers of greenfinches, chaffinches and siskins have generally been in double figures, with smaller numbers of goldfinches, a couple of pairs of bullfinches (bullfinches pair for life, so are usually seen as a couple), and the occasional brambling, the chaffinch’s Scandinavian cousin.
A greenfinch with trichomonosis (picture from a bird food supplier)
But then I noticed one greenfinch acting rather differently from the rest. Finches (and other small birds) tend to flock together through the winter, and a group of mixed species will move through the area visiting different sources of food - which is one reason why one moment there may be no birds at all in your garden, and the next it’s absolutely full of them. This bird, however, was not moving around with the flock but staying close to the feeders. It looked listless and sad, and its feathers were puffed up, making it look like a little ball of a bird.
Although it stayed close to the feeders, it didn’t actually seem to be using them much. This was a rather poorly bird, that much was clear. And probably therefore a bird suffering from the disease trichomonosis, which has greatly reduced greenfinch numbers in our gardens in recent years. I had been expecting to see signs of this disease sooner or later, so I’m sad but not surprised.
Trichomonosis is caused by a protozoan parasite, and affects the throat and gullet of the bird, preventing it from eating successfully. Affected birds may regurgitate food, and other birds may then consume it, which is a prime cause of the disease spread, as is poor hygiene at feeding stations, bird baths etc. This is the disease of pigeons known as canker, or as frounce when seen in birds of prey. It has been known as a disease of cage birds for some time, but has been identified as affecting greenfinches (and other birds such as chaffinches and siskins) since 2006. The parasite cannot live long outside its host, which means that simple hygiene measures can meet with a reasonable degree of success. It does not affect human beings or other mammals.
So what should I do? I try to make sure I clean feeders regularly, but I could improve hygiene further by using an appropriate disinfectant product. It’s important to leave feeders to air-dry before refilling. Bird baths, also, should be emptied and air-dried on a regular basis. Ground-feeding birds are particularly vulnerable, so cleaning the ground beneath feeders (ours are on paving) will help - but, even better, move feeders around the garden; that will help prevent the build-up of contamination in any one place. I think the RSPB recommends stopping feeding so that birds are forced to feed elsewhere at a lower density; in reality, though, they may simply move on to other garden feeding stations, where perhaps no hygiene measures are in place. So I shall improve hygiene, keep feeding, and hope for the best.