Andre Thiel’s scientific contributions

Capsule A specific suite of moorland management prescriptions had no clear positive impact on breeding birds over ten years. Aims To test the expectation that a combination of grazing, and burning/cutting manipulations, the blocking of drains (affecting habitat quality and foraging resources) and the control of some predators (affecting survival and breeding success) will lead to an increase in numbers of breeding birds on 9.5 km² of moorland in Scotland. Methods General Additive Modelling was used to compare bird population trends at the managed site against a ‘control’ of moorland-specific background trends (spatially and temporally smoothed) derived from an extensive UK-wide bird monitoring programme. Changes in vegetation, the effectiveness of predation control and influences of disturbance were also examined to attempt to identify potential mechanisms for population size changes. Results Breeding populations for most species showed either a more negative trend at the managed site (Red Grouse, Skylark and Meadow Pipit) or no significant difference was detected (European Golden Plover, Eurasian Curlew, Common Snipe and Winter Wren) when compared to moorland-specific background trends. Stonechats and Carrion Crows increased, despite the latter being actively removed as part of predation control measures. No general change in the vegetation was detected and no reasonable habitat-based cause for the observed declines in some species was apparent. There was also no convincing evidence for a negative effect on moorland birds of disturbance from a nearby mine. As crow control failed to stem their increase and with supportive evidence for a decline in the breeding success of Red Grouse, it is suggested that the control of predation was ineffective and may have contributed to some species declines. Conclusion There has been wide advocacy of, and considerable resources (e.g. through agri-environment schemes) devoted to, moorland habitat management for birds and yet declines continue. However, there are practical difficulties of establishing management that is effective in increasing moorland bird abundance. It appears likely that in areas where those birds are vulnerable to predation and its control is not effective, expectations of increasing bird populations in response to habitat management alone may be unrealistic.

Capsule A minimum of four constant‐effort‐search survey visits are required to generate reliable population estimates of breeding birds on moorland that are not subject to biases associated with varying levels of detectability through the season.Aims To investigate the influence of the number and the combination of survey visits on the population estimates of breeding birds on moorland.Methods Four constant‐effort‐search surveys (80–100 minutes per km per visit) of moorland in southwest Scotland were undertaken in each of six years, 2003–2008. Using standard protocols, the numbers of apparent territories that would have been identified for each possible combination of survey visits were determined.glms were used to assess the influence of the frequency of survey visits, and different combination scenarios on the derived population estimates for Red Grouse, European Golden Plover, Common Snipe, Eurasian Curlew, Sky Lark, Winter Wren and Stonechat. Independent assessments of population density were made by transect sampling for Red Grouse and Sky Lark.Results Robust population estimates were possible from three survey visits for European Golden Plover, Eurasian Curlew and Stonechat. However, there were differences between species in the seasonal variation of their detectability. Four survey visits would underestimate the populations of Red Grouse (probably by 67–91%), Sky Lark (probably by 31–61%) and Winter Wren (by an undetermined proportion). Common Snipe were also likely to be underestimated after four survey visits, but the value of the derived estimate as an index of population density deserves further investigation.Conclusions If there is a need to carry out a multi‐species survey on moorland, we suggest that a minimum of four survey visits is required to ensure the derivation of reliable population estimates for a suite of the most readily detectable species. Population estimates derived from three or fewer survey visits risk biases through uneven sampling in periods of differing detectability. With evidence for changes in the breeding phenology of birds associated with changing climate or weather patterns, it arguably becomes more important to ensure that surveys sample an adequately broad period of the breeding season.