Chlamydiosis is caused by the intracellular bacterium Chlamydia (previously Chlamydophila) psittaci . Birds are natural hosts of C psittaci, and a wide range of avian species is susceptible to infection. C psittaci can cause severe disease in humans (in other words, it is a “zoonosis”) where captive psittacines (parrots and their allies) have most often been implicated as the source of infection. C psittaci infection is prevalent in wild pigeons in Britain but its prevalence in songbirds is unknown.
Ten songbird mortality incidents were investigated. In each of these chlamydiosis was suspected on the basis of the species “assemblage” (sick or dead robins and/or tits and/or dunnocks) and the finding post mortem of an enlarged liver and/or spleen in affected birds.
Chlamydia-specific PCR tests were conducted and as a result Chlamydia sp. infection was diagnosed in birds from seven of the incidents.
All the Chlamydia sp. positive incidents reported in this account occurred at locations where wild birds were being provided with supplementary food. Six of the seven sites were private gardens.
This report should not discourage members of the public, including those who read this blog, from providing food for garden birds. If practised properly, this can be very beneficial – both to the birds that thereby receive supplementary feeding and to those who put out the food and enjoy watching the avian visitors that are attracted to it. However, hygiene is important and this comprises:
1) regular cleaning of bird-tables and other feeding areas
2) providing food of high quality (Haith’s can advise on its superclean diets)
3) not overfeeding birds, because they need to look for food in the garden and hedgerows, not to depend solely on human intervention.