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THE PAST 15 YEARS HAVE SEEN greenfinches shift from ubiquitous garden visitors to something of a rare sight. New research from the British Trust for Ornithology (BTO) and the ZSL Institute of Zoology bolsters the evidence that the infectious disease behind their huge decline is spread by the very bird feeders that attract them to our gardens. <\/p>\n\n
Trichomonosis is caused by a singlecelled parasite that creates lesions in the birds\u2019 throats. These interfere with feeding, leading to death by starvation. It was first detected among UK greenfinches in 2005, when the suspicion was that they had been infected by pigeons, the primary hosts of the disease, at garden feeders. <\/p>\n\n
Chaffinches are another garden visitor susceptible to lethal infection, although their decline was not evident until about 2014. \u201cThey were our second commonest species; they\u2019re now our fifth,\u201d says the BTO\u2019s Hugh Hanmer. \u201cWe\u2019ve lost about two and a half million pairs between the two species.\u201d <\/p>\n\n
The new study, published in Scientific <\/em>Reports, <\/em>draws on data from the BTO\u2019s Garden BirdWatch and breeding bird surveys, as well as nest and ringing records. It shows that the finches\u2019 declines coincide with the rise of trichomonosis infections among garden visitors, which in turn reduced adult survival. The steepest declines occurred in garden habitats. The \u201clogical conclusion,\u201d says Hanmer, is that garden feeders are a major source of infection. <\/p>\n\n He is concerned that the infection might yet spread to other, rarer species, less able to weather a population crash. \u201cThe hawfinch is probably the obvious one,\u201d he says. \u201cAnd there\u2019s evidence that they can catch it.\u201d <\/p>\n\n There is little doubt that garden feeding brings benefits to bird and human populations alike. But the study shows there are also costs. \u201cIt\u2019s a trade-off,\u201d says Hanmer. \u201cWe are currently talking about how to give better guidance.\u201d This might, for example, mean advising householders to feed birds only in winter. But it\u2019s not impossible that the cons prove to outweigh the pros. <\/p>\n\n \u201cBTO is a science-led organisation, and if that\u2019s what the facts were to tell us, then that is what we would communicate,\u201d says Hanmer. \u201cBut we\u2019re nowhere near that at the moment.\u201d <\/p>\n\n SB <\/strong><\/p>\n\n BTO to reconsider guidelines to householders in the light of new research on trichomonosis transmission 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to reconsider guidelines to householders in the light of new research on trichomonosis 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