Contents of report
Breeding Bird Survey
Common Birds Census
Constant Effort Sites
Nest Record Scheme
Waterways Bird Survey
What the categories mean
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4.1 The new alert system
This report is the first to use the new system of alerts agreed after a series of extensive discussions between the providers and users of population monitoring information in the UK.  The system provides alerts to population declines of 25-49% and of  >50% over short, medium and longer terms (5 years, 10 years and 25+ years respectively).  These help highlight the scale and timing of declines as an aid to interpreting the trend graphs presented.   For example, a species that triggers an alert over 25 years but not over the past 10 or 5 years, declined at some point in the past, but has not yet recovered, but another that triggers alerts over 25, 10 and 5 years is still undergoing a potentially serious population decline.  For the former species, conservation agencies must try to identify factors that will help the species recover, whereas for the latter species, it is initially urgent that the conservation agencies identify how to halt the current decline before considering how to increase the population.  For species that trigger short-term alerts only, these are early warnings to the conservation agencies that there might be a problem developing, although there is still a chance that the declines might be due to chance fluctuations.  However, if an identifiable suite of species all showed rapid short-term declines, then this might be a stronger early warning signal that the conservation agencies should perhaps consider sooner. 
Thus these alerts are important for the conservation practitioners who need to prioritise the needs for conservation action.  But we also hope that these alerts will prove useful to readers of the report, more generally. 
In this discussion:
1) We first describe the key alerts that are raised for population declines over the last 30 years on all CBC plots combined.  This is the time period most relevant to the UK conservation because it is comparable to the time period being used in the revision, currently underway, of the Red and Amber listings of birds of conservation concern. 
2) The aim is to:
  a) highlight those species that are potentially new candidates for conservation listing because of rapid or moderate declines in abundance, and
  b) to discuss those species that are candidates to change their conservation status.
3) We then discuss the other main alerts covered in the report:
  a) 30-year alerts raised from CBC farm and woodland plots separately,
  b) WBS alerts over 23 years,
  c) CES alerts over 14 years, and
  d) BBS changes over 5 years,
4) Finally we discuss:
  a) rapidly increasing species,
  b) changes in breeding performance and
  c) summarise the overall patterns found.


The report should be cited as: Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Bashford, R.I., Beaven, L.P., Freeman, S.N., Marchant, J.H., Noble, D.G., Raven, M.J., Siriwardena, G.M., Thewlis, R. and Wernham, C.V. (2001) Breeding Birds in the Wider Countryside: their conservation status 2000. BTO Research Report No. 252. BTO, Thetford. (

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Last updated: 23 October, 2001

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