Abstract

Recent declines in Greenfinch Chloris chloris numbers have been attributed to the spread of trichomonosis, and most contemporary summaries of the status of the Greenfinch in the UK concentrate on this steep decline, which began around 2005. Data from 2010–20 have shown a 65% decline in breeding numbers in the UK. Here, longer-term trends are examined, and data are presented that suggest, for Kent in particular, that a decline in breeding, passage and wintering numbers has persisted for at least 50 years. At present, there is no structured survey to monitor populations of terrestrial bird species in the UK during the non-breeding season and, citing the lack of information on numbers of non-breeding Greenfinches in the UK, this paper highlights the desirability of such a survey.Breeding population trendsThe general consensus is that, before 2005, the number of breeding Greenfinches Chloris chloris in Britain had undergone an increase over a period of several years, prior to which they were relatively stable, in contrast to other seed-eaters such as Linnet Linaria cannabina and Tree Sparrow Passer montanus, which were declining sharply. Hanmer et al. (2022), for example, wrote: ‘Prior to 2006, population trends for had undergone long-term increases.’ The BTO BirdTrends report for 2010 (Baillie et al. 2011) stated: ‘Greenfinch abundance varied little up to the mid 1990s’ and ‘more recent CBC/BBS data indicate population increases widely across the UK, followed by a sudden sharp fall induced by a widespread and severe outbreak of trichomonosis that began in 2005.’ Similar wording has been used annually in BirdTrends reports since then. From Common Birds Census (CBC) data, Fuller et al. (1995) and Siriwardena et al. (1998) had earlier reported little change in Greenfinch abundance. Using data from 1968 to 1991, Fuller et al. found a 6% decline in Britain as a whole and an 8% decline in southeast England. Siriwardena et al. found a non-significant 3% increase between 1968 and 1995. One slightly contradictory view came from Brown & Grice (2005), who included a chart based on English CBC data showing decline between the mid 1970s and mid 1980s.The implication of stability prior to the mid 1990s is somewhat contrary to the graphs shown in successive BirdTrends reports. Data downloaded for the combined CBC/BBS indices from the 2020 report (Massimino et al. 2022) suggest a decline of over 20% between 1966 and 1985, followed by a rise of 58% between 1985 and 2005, before the steep decline from 2005 onwards (fig. 1). There are, however, doubts about the reliability of CBC data in respect of their geographical coverage, which is biased towards lowland farmland, and the analytical methods used. The shaded area in fig. 1 represents 85% confidence limits; at that level, the decline from 1966 to 1985 is significant, if only just, in that the upper confidence limits during 1984–86 are a little lower than the lower confidence limits in 1966–68.