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4. DISCUSSION

4.6    Discussion of trends

4.6.1 Candidates for conservation listing

The new analyses presented in this report suggest that conditions have worsened sufficiently for several new species to be considered as potential candidates for listing as species of conservation concern when the lists are revised.  As described in section 6, the species listed as Priority Species under the Government’s Biodiversity Action Plan (BAP) are broadly equivalent to those that are Red-listed by the conservation Non-Governmental Organisations (Gibbons et al. 1996), and those listed as (non-priority) BAP Species of Conservation Concern are broadly equivalent as Amber-listed species on the NGO list. 

Under the criteria used at the first listing Yellowhammer would come straight onto the Red list, with a population decline of >50%, and Mistle Thrush, Willow Warbler and Cuckoo would come onto the Amber list, with population declines of >25%.

However, under the current criteria, several species would not be included although they certainly warrant urgent conservation attention.  These include House Sparrow (candidate Red), and Yellow and Grey Wagtails (candidate Red and Amber listing, respectively), which have undergone substantial population declines, but have been monitored for slightly less than the previously required 25-year period. Whitethroat (candidate Red) could be included because it suffered a large population crash more than 25 years ago, but has since shown only a poor recovery, and certainly a much slower rate than would be expected if conditions had not remained poor for the species (conditions may have declined in the UK). 

Then there are a number of species that have declined substantially, but the monitoring schemes may not be representative for the whole population.  However, substantial declines in part of the population, when there is insufficient information to be sure that such declines have not occurred for the remainder, could be a valid reason for conservation listing under the precautionary principle.   The species that are potential candidates for Red listing under this criterion are: Redpoll and Tree Pipit; and for Amber listing are: Meadow Pipit and Lapwing.

4.6.2     Candidates for changed conservation listing

Three species are candidates for upgrading from Amber to Red listing: Starling, and Willow and Marsh Tits, all three having declined substantially more than 50% over the past 30 years.  Woodcock is also a candidate for upgrading, although it is a species for which the monitoring programme may not be representative of the population in the UK as a whole: it was previously listed because of a decline in distribution, but the CBC now shows a decline in population size of >50%.

Two species warrant downgrading from Red to Amber listing, if 30 years is used as the period over which declines are assessed, but not because of a substantial improvement in their population trajectories: Bullfinch and Reed Bunting. The same applies to Kestrel, which shows little change over 30 years because it was still recovering from the impact of organochlorine pesticide effects in the early 1960s.  However, it still shows a decline of >25% over the last 25 years, because this is measured from the period at which it had generally recovered.

The population trajectories of two species are sufficiently changed to justify removal from the conservation listings: Swallow and Goldfinch.  Both species show relatively large-scale medium-term population fluctuations that resulted in their previous listings, but populations have recovered sufficiently to show no long-term trend over the past 30 years. The precautionary principle requires that alerts should be raised so that the statutory conservation agencies and non-governmental conservation bodies are aware of potentially worrying declines, even if they are later found to be just part of the natural range of fluctuation. Such alerts are increasingly unlikely to occur as monitoring time series increase in length and the presence of such medium-term fluctuations become more apparent for those species affected.

4.6.3     Accelerating declines

A source of considerable concern for conservation agencies should be that several species that are on the lists of conservation concern have actually accelerated their decline since the list was drawn up in 1996.  This is despite the presence of costed government Biodiversity Action Plans for some of them.  Thus the Red-listed Grey Partridge, Turtle Dove, Tree Sparrow, Bullfinch and Corn Bunting all show population declines of greater than 25% on CBC or BBS plots over the last 5 years.  Kestrel, Starling and Willow Tit, currently Amber-listed (but the last two, candidates for Red-listing), also show declines of greater than 25% over the past 5 years on CBC or BBS plots. 

Similarly, several species that have been in decline for several years, but were not considered sufficiently well-monitored throughout the UK to be listed previously, have shown a particularly large percentage decline (of >25%) over the last 5 years on CBC or BBS plots: Yellow Wagtail, Tree Pipit and Redpoll.  Also, two candidate species for Red or Amber listing have reached that state as a result of accelerated declines over the last 5 years: Cuckoo and Yellowhammer.

4.6.4     The role of breeding performance

In general, breeding performance appears to show a density dependent response to population changes.  As populations decline, breeding performance tends to improve, but as populations increase, breeding performance tends to decline.

However, there are a number of species for which declines in breeding performance are likely to driving the population declines (Linnet, Lapwing and possibly Nightingale) or helping to inhibit recovery (possibly Reed Bunting and Whitethroat).  The importance of declining breeding performance for declining Redpoll, Yellow and Pied Wagtail and for farmland Moorhen populations is, as yet, undetermined. 

There are also a number of species for which increasing breeding performance may be helping to drive population expansion.  This applies to the predatory Grey Heron, Sparrowhawk and Buzzard; the corvids Jackdaw, Magpie, Crow, Jay and Rook; the seed-eaters, Collared Dove, Stock Dove, Chaffinch and Woodlark; and the insectivores, Robin, Redstart, Nuthatch, Great Tit, Blue Tit and Long-tailed Tit.

For a few species, long-term population data are not available and changes in breeding performance from the Nest Record Scheme may provide a potential warning of population declines, either because they have the potential to drive population decline (Red-throated Diver and Ringed Plover) or because they are the result of density dependent changes (Stonechat, Whinchat, Wheatear, Tawny Owl and Ring Ouzel).  The importance of the substantial declines in productivity of Greenfinch, Blue Tit, Sedge Warbler and Garden Warbler is unclear at the moment, but warrant close attention.

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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. (http://www.bto.org/birdtrends)

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