Chaffinch

According to the RSPB, trichomonosis, an avian disease caused by a parasite called Trichomonas gallinae, has reduced the UK’s chaffinch population by 34% in the last decade.

Audio: Common Chaffinch by Krzysztof Deoniziak (CC BY-NC-ND 4.0 DEED) xeno-canto.org XC884915

Recent research has indicated that the disease began in the UK (spillover from a condition found in domestic poultry and in pigeons) and spread eastward into continental Europe. Millions of chaffinches visit Britain during the winter to avoid the harsh European winter and trichomonosis has travelled with them when they returned to their summer breeding territories.

Until 2012, the chaffinch was the UK’s second most common species of bird (the first was and still is the house sparrow) but since then it has fallen to fifth place. Population modelling has shown that this decline is the outcome of reduced adult survival, almost certainly the result of trichomonosis infection, and that it is most evident in urban habitats where supplementary feeding is more available than it is in urban areas.

Gatherings of birds around garden feeders create the ideal conditions in which the parasite is passed on. While our impulse is to help, we are too often doing harm.

Here is a link to the British Trust for Ornithology’s page about trichomonosis, including important ways in which we can help.