BRANTA — Lucy J. Wright

Productivity and population dynamics of Woodlarks Lullula arborea breeding in Breckland

Institution: University of East Anglia, UK
Supervisors: WJ Sutherland, PM Dolman
Details: PhD 2006 (Completed)

Address: BTO, The Nunnery, Thetford, IP24 2PU, UK (Oct 2012) Email

Subject Keywords: climate change, phenology, nest predation, habitat switching, forest management, farmland set-aside, conservation
Species Keywords: Wood Lark Lullula arborea

 

Abstract

Woodlarks Lullula arborea are ground nesting, multi-brooded passerines of European Conservation Concern. Around 30 % of the UK population breeds in the Breckland region of East Anglia. Woodlark populations have increased dramatically in the region during the past 35 years. This thesis investigates the mechanisms and causes of the observed changes in woodlark population size since 1970.

Woodlark breeding habitat in Breckland has varied historically between heathland, plantation forest clear-fells and, more recently, farmland set-aside fields. Currently all three habitats are occupied. Farmland set-aside could support a significant proportion of the Breckland population. There was no significant difference in reproductive output between heathland and forest clear-fells. However clutch sizes may be smaller on farmland, perhaps an indication that farmland is sub-optimal compared to the other habitat types and that a buffer effect is operating.

Habitat occupancy within Thetford Forest was investigated, in order to determine the factors influencing woodlark abundance in clear-felled coupes, including stand age, vegetation, soil type and coupe area.

Factors affecting productivity were considered for birds breeding in Thetford Forest. Nest success declined significantly over the 35 years of the study. Clutch size was reduced at higher population density, and woodlarks laid larger clutches later in the breeding season. Nestling survival rates were lower on younger stands.

Woodlarks bred earlier in warmer springs. Breeding success was controlled mainly by predation, but also by weather. Simulation modelling of repeat nesting attempts demonstrated that changes in predation rates had a greater effect on annual productivity than the combined effects of weather. Mortality was higher in cold winters, but annual recruitment rates were higher after 1988 compared to the period up to 1988 (controlling for the effect of winter temperature). The availability of winter stubble fields on farmland from 1989 (due to set-aside) may have allowed survival rates to increase.
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