Greenfinch by Edmund Fellowes

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 indicate six changes to the alerts since BirdTrends 2019, affecting six different species.

• For the amber-listed Meadow Pipit, the 51-year CBC/BBS decline for England now raises a high alert. The 25-year trend continues to raise a lower level alert.
• The 25-year CBC/BBS UK decline for Marsh Tit now raises a lower alert, with the trend suggesting that the rate of decline may have slowed slightly. However, the 51-year CBC/BBS trend for this species continues to raise a high alert.
• The amber-listed Dipper again raises formal lower level alerts, based on the 43-year WBS/WBBS trend. This species has raised a similar alert in previous reports but did not raise a formal alert in BirdTrends 2019 as the estimates were not statistically significant due to wide confidence intervals.
• The 42-year WBS/WBBS trend for Little Grebe and the 51-year CBC/BBS trend for Garden Warbler again raise no formal alerts in this report. As for Dipper, both species have raised formal alerts in some of the recent BirdTrends reports but not in others, as the confidence intervals have changed and hence the estimates have not always been statistically significant. 
• The amber-listed Oystercatcher is listed in Table A3 and raises a formal lower level alert as the 25-year decline now greater than 25%.

Amber and red listings use similar criteria and were reviewed in 2015. This report, using five further year's data not available to BoCC4, suggest potential updates to current conservation concern for Snipe, Redshank, Sparrowhawk, House Martin, Willow Warbler and Greenfinch (though note that the trend for Snipe is based on a small sample) and possibly Sedge Warbler. In addition, although a long-term CBC/BBS trend is not available for Swift, the 23-year BBS trend suggests a potential update to the current conservation concern level for this species (from amber to red).

The number of species for which potential updates to current conservation concern are suggested by the alerts has increased in recent years (Table 1).

Table 1: Summary of potential updates to BoCC4 conservation listings resulting from changes to population trends, based on alerts in recent BirdTrends reports. Note that the future update decisions will not necessarily follow the alerts in all cases but may take additional information into account, particularly for species for which alerts are based on a small sample, or long-term results are only available for England and not for the UK as a whole.

	2017	2018	2019	2020
Amber to Red	3	4	4	6
Green to Red	0	1	1	1
Red to Amber	1	2	2	2
POTENTIAL CHANGE TO RED LIST	+2	+3	+3	+5
Green to Amber	2	1	3	2
Amber to Green	2	2	2	2
POTENTIAL CHANGE TO AMBER LIST	-2	-3	-1	-4
POTENTIAL OVERALL CHANGE TO NUMBER OF LISTED SPECIES	0	0	+2	+1

Alerts from WBS/WBBS (Table A4) are unchanged, apart from the changes in alert status for Little Grebe and Dipper which are described above. 

The alerts for CES (Table A5) show changes from BirdTrends 2019 for two species. The 25-year and 34-year trends for Chaffinch now both raise a high level alert, as does the 25-year trend for Sedge Warbler (the 34-year trend for Sedge Warbler continues to raise a lower level alert, as in BirdTrends 2019).