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Recent changes to alerts
The 25-year trend for Garden Warbler now raises an alert for breeding decline, the first such alert
for this species.

The BirdTrends report raises species alerts for population change to conservation bodies when the best available estimates of long-term decline are statistically significant and pass criteria set at -25% and -50%.

Species with declines close to these threshold values often change category between years. Discussion tables A1–A3, however, indicate just six changes to the long-term alerts since BirdTrends 2014.

  • A CBC/BBS trend for Nightingale has not previously been calculated. It indicates high alerts for population decline over the 46-year and 25-year periods. The species was upgraded from amber to the red list in 2015.
  • For House Martin, the 25-year CBC/BBS decrease of >50% is now statistically significant and so, like the 46-year trend, raises a high alert. House Martin remains amber listed after the 2015 review.
  • For Little Grebe, the 25-year WBS/WBBS decline of >25% has become statistically significant and so raises an alert. The species was downgraded from amber to green in 2015, although the long-term WBS/WBBS trend raises a high alert.
  • For Garden Warbler, the significant 25-year CBC/BBS decline has now passed the 25% threshold, raising a population-change alert for this species for the first time. Garden Warbler is green listed.
  • For Tawny Owl, the 25-year trend has dropped to <25% and so no longer raises any alert. Tawny Owl is amber listed.
  • For Tree Sparrow, the 25-year change is now less than a 50% decline and so raises only the lower level of alert. Tree Sparrow is red listed and its long-term decline remains severe.

Amber and red listings use similar criteria and have only just been reviewed. This report, using a further year's data not available to BoCC4, already suggests potential updates to current conservation concern for House Martin, Little Grebe, Garden Warbler and Tawny Owl.

Alerts from WBS/WBBS (Table A4) are unchanged except that the decline for Sedge Warbler has passed the 50% mark and consequently now raises the higher level of alert.

For CES there are additional lower-level alerts for Greenfinch, Song Thrush and Whitethroat over the 25-year period and for Whitethroat also over the full CES period (29 years).


This report should be cited as: Robinson, R.A., Marchant, J.H., Leech, D.I., Massimino, D., Sullivan, M.J.P., Eglington, S.M., Barimore, C., Dadam, D., Downie, I.S., Hammond, M.J., Harris, S.J., Noble, D.G., Walker, R.H. & Baillie, S.R. (2015) BirdTrends 2015: trends in numbers, breeding success and survival for UK breeding birds. Research Report 678. BTO, Thetford. www.bto.org/birdtrends