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4.6    Discussion of trends

4.6.1 Candidates for conservation listing

The new analyses presented in this report suggest that several species should be considered as potential candidates for addition to the revised conservation lists currently being developed by the conservation agencies and conservation Non-Governmental Organisations (NGOs). Yellowhammer and Lesser Spotted Woodpecker have both exhibited rapid population declines of greater than 50% over the last 25 years, and Mistle Thrush, Cuckoo, Willow Warbler and House Sparrow have all exhibited population declines of greater than 25% over this period.

While the above species are obvious candidates for addition to the conservation lists, the status of other species is less clear. The Waterways Birds Survey (WBS) has identified rapid (>50%) declines for Little Grebe, Grey Wagtail and Yellow Wagtail populations, but as only 24 years of data are presently available from this scheme, the current acceptance criteria, which specify a 25 year trend, exclude them from the conservation lists. Other BTO monitoring schemes have identified population decreases of greater than 50% for Lesser Redpoll, Goldcrest and Tree Pipit, and of between 25% and 49% for Meadow Pipit and Lapwing. However, as the populations of these species may only be partially sampled by the respective schemes, the reported trends may not be representative of the conservation status of these species at a national level.

4.6.2     Candidates for changed conservation listing

Three species - Starlings, Willow Tits and Marsh Tits - previously listed as exhibiting moderate declines (>25%) now appear to be declining rapidly, decreasing in number by greater than 50% over the last 25 years. Conversely, the population trajectories of two species - Swallow and Goldfinch - have changed sufficiently to justify their removal from the conservation listings. Both species exhibit relatively large-scale medium-term population fluctuations that resulted in their previous listings, but populations have since recovered to the extent that no long-term trend is detectable over the last 25 years.

4.6.3     Accelerating declines

A source of considerable concern is that several species that appear on conservation lists have actually accelerated their decline since the lists were drawn up in 1996 (JNCC 1996, Gibbons et al. 1996), despite the presence of costed government Biodiversity Action Plans for some of them.  Thus the Red-listed Grey Partridge, Bullfinch and Corn Bunting all show population declines of greater than 25% on CBC or BBS plots over the last 5 and 6 years respectively.  Starling and Willow Tit also show declines of greater than 25% over the past 5 or 6 years respectively on CBC or BBS plots. 

In addition, two species that have been in decline for several years, but were not considered sufficiently well-monitored throughout the UK to be listed previously, have exhibited declines of >25% over the last 5 years on CBC plots (Redpoll) and WBS plots (Yellow Wagtail).

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 be driving the population declines (Linnet and Lapwing) or helping to inhibit recovery (possibly Reed Bunting and Whitethroat).  The importance of decreases in breeding performance for declining Redpoll and Yellow Wagtail populations and for farmland Moorhen populations is, as yet, undetermined. 

Increasing breeding performance may be helping to drive population expansion of a number of species:  the predatory Grey Heron, Sparrowhawk and Buzzard; the corvids Jackdaw, Magpie, Crow and Rook; the seed-eaters Collared Dove, Stock Dove 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 declines (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 warrants close attention.

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This report should be cited as:
Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Beaven, L.P., Downie, I.S., Freeman, S.N., Leech, D.I., Marchant, J.H.,
Noble, D.G., Raven, M.J., Simpkin, A.P., Thewlis, R.M. and Wernham, C.V.
(2002) Breeding Birds in the Wider
Countryside: their conservation status 2001. BTO Research Report No. 278. BTO, Thetford. (http://www.bto.org/birdtrends)

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