Greenfinch - Portland Bill, 1st February 2016 © Martin Cade
We've remarked quite often just lately on the alarming demise of the Greenfinch at Portland, perhaps illustrated no better than by events at the Obs garden where from being until relatively recently a familiar and numerous breeding bird - as well as a common passage migrant - the species has declined to the extent that no young were raised in 2015 and just two birds were trapped and ringed between last April and today. Although the current decline - which is attributed to the emergence of the respiratory disease trichomonosis - has been worryingly precipitous, we were intrigued upon examining the Obs garden ringing totals to discover that it's not unprecedented here:
The totals in the early years of the Obs - certainly until the early 70s - are probably best discounted from any analysis since the habitat then was considerably less Greenfinch-friendly than it has been since, whilst there was also a good deal less ringing effort in that era than there is now. However, what's abundantly clear from the totals is a peak in numbers through the late 70s, followed by a steep decline through the 80s - a situation mirrored by events in the last decade. Thus far, we haven't discovered any explanation for the decline during the 80s, but the subsequent recovery certainly offers hope for the future. To contrast with the fortunes of the Greenfinch, we included the Goldfinch totals on the graph above - it seems as though they're the ones inheriting the Obs garden in the absence of the stricken Greenfinches!
