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1.2 The value of combining results from different monitoring schemes
   
  It is becoming increasingly obvious that simply monitoring changes in the size of a population does provide sufficient information on which to base effective conservation strategies is not enough for conservationists (Goss-Custard 1993). The monitoring of breeding performance and survival rates are essential to allow efficient interpretation of changes in population size (Temple & Wiens 1989) and, in the case of long-lived species, to provide early warning of impending changes in population size (Pienkowski 1991).
     
  Without access to good long-term datasets concerning breeding performance and survival, remedial conservation action has to be taken without a sound basis or must wait for detailed investigative research to be undertaken. In addition, for long-lived species, declines in population size may only occur after long periods of low survival or reproduction.
     
  The classic example is that of the Peregrine, which in the UK suffered from poor breeding performance during the 1940s and 1950s due to DDT contamination. This decreased the buffering capacity of the non-breeding population to withstand the severe mortality of breeding adults that occurred due to cyclodiene poisoning from the middle 1950s onwards (Ratcliffe 1993). Monitoring of breeding numbers did not reveal the problem as efficiently as an "early warning" based on the monitoring of breeding performance (Pienkowski 1991).
     
Another recent example of a decline in breeding performance preceded a decline in population size is provided by the catastrophic breeding failures of seabirds, and particularly Arctic Terns, in Shetland (Monaghan et al. 1989, Walsh et al. 1995).
     
  Farmland birds
 

During the mid-1980s the BTO identified rapid declines in the population sizes of some farmland bird species (O'Connor & Shrubb 1986, Fuller et al. 1995), but the causes of the declines were not readily apparent. The BTO has been able to investigate the causes of these declines because of its long-term historical databases (Siriwardena et al. 1998a, 2000). The alternative approach of funding intensive studies of the 10-20 species separately would have been very costly, taken several years to complete and would not necessarily have been representative of the UK.

The investigation, which was undertaken jointly with Oxford University, and funded by the UK Government, looked at changes in population size, breeding performance and survival rates of a variety of species in relation to changes in farming practice. The study showed that each species has tended to respond to different aspects of the agricultural environment but that these aspects tended to be symptomatic of the trend towards intensification and regional specialisation. Overall, declines in survival rates were found to be the main factor driving population declines in these species with the exception of the Linnet, for which the main factor appears to have been a decline in nesting success at the egg stage. The study was therefore able to identify areas for future research, thereby helping conservation bodies to target their scarce resources in the most efficient manner.

     
 

Other examples where the combined (or integrated) analysis of BTO datasets has helped to pinpoint the causes of population declines include:

  • Declines in breeding performance appear to have driven the population decline of Lapwing (Peach et al. 1994).
  • Declines in survival rates during the first year of life are sufficient to have driven the population decline of Song Thrush (Baillie 1990, Thomson et al. 1997).
  • Declining over-wintering survival, associated with below average rainfall in the Sahel wintering quarters, was the most important factor determining changes in Sedge Warbler abundance (Peach et al. 1991).
   
  Biodiversity Action Plans
  The ability to quickly determine the stage of the life-cycle which is most affected during population declines is particularly important for the conservation agencies considering the plight of species listed on conservation listings (JNCC 1996; Anon. 1995, 1998). (These lists were drawn up using data from the BTO's Common Birds Census (and other sources of information) to prioritise bird species of conservation concern). Indeed, analysis of BTO datasets is included as a key point in several of the UK Government's Biodiversity Steering Group Action Plans for rapidly declining species.
     
  Of course, this is not the only function of the BTO's Integrated Population Monitoring programme. Once conservation actions have been initiated, their successes will be monitored and assessed against the background information provided by the BTO's long-term schemes. This is the only way that conservation bodies can measure the effectiveness of their actions at a national scale in a cost-effective manner.

 

Next Section - 1.3 The aims of this report

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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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