Designing working landscapes with important birds in mind

Posted by Matt Geary

Species distribution modelling has become an invaluable tool in conservation science over the past decade. It has been widely used to delimit species' ranges, identify potential survey areas and predict future range-shifts due to climate change. Species distribution models have also been used to identify suitable habitat features for focal species and to suggest future management actions. In this paper, published in the latest issue of Ibis, we extended these ideas using multi-scaled models to 'design' landscapes for a species with complex habitat requirements, the black grouse.

Black grouse Tetrao tetrix is a medium-sized gamebird which has experienced serious population declines across western Europe over the last 100 years. In Britain populations are thought to have been negatively affected by land-use changes in the uplands, particularly canopy-closure in commercial plantation forests and increases in grazing pressure. Black grouse is a bird of the forest-edge and requires a habitat mosaic consisting of woodland, moorland, scrub and upland bog among other habitat types. Because of these complex requirements it can be difficult to assess habitat combinations for black grouse, never mind isolate one particular habitat mix.

Male black grouse in snow. Photo: Steve Garvie

Black grouse are relatively faithful to territories across years and compete for mates at traditional, communal display sites, within these territories, each spring. We used records of these territories (kindly provided by the volunteers at the Perthshire Black Grouse Study Group) along with habitat data from satellite imagery to fit species distribution models for black grouse within our study area in Perthshire, Scotland. We used MaxEnt to fit the models and performed the modelling at six radii around lek sites (between 0.2 and 3 km). We tried to identify habitat features which were associated with a high relative suitability for black grouse at each of these scales.

  

A view of the study area in Perthshire from Ben Vrackie. Photo: Jan Zeschky.

With this information we could start to show how habitat features in different parts of black grouse territories could contribute to the overall suitability of the landscape for black grouse. As you might expect, different habitat types were suitable at different proportions in different parts of our 'ideal' territory. Close to display sites, large proportions of several individual habitat types or varied habitat mixtures could all result in high relative suitability for black grouse. One habitat type in particular, though, was always detrimental at small distances from the lek. Closed canopy forestry in these locations reduced the suitability for black grouse, most probably because this sort of forestry would strongly reduce the visibility of the lek site. Dense commercial forests are very difficult for black grouse to move through and where these forests have hard edges they prove difficult to use as a refuge from predators. These factors would all be detrimental close to a display site.

   

Caledonian pine forest in North Scotland. Open canopy forestry with a rich understorey

At larger distances from the lek, however, larger proportions of forestry become acceptable. We also found that, while closed-canopy forestry might not be suitable close to the lek, at moderate distance a relatively large amount of open-canopy forestry, such as native woodland, would be less damaging. We also identified more than one habitat combination which could result in large or growing black grouse leks. Through use of multi-scaled models, we were able to consider a range of habitat mosaics which have the potential to be beneficial for this species. We believe that the messages from this study translate well across bird species. Combining landscape-scale conservation, translated into policy for example, with fine-scale habitat management can benefit not only individual groups but contiguous populations of species and ensure their survival into the future.

Photo: Billy Lindblom

Matt Geary finished his PhD at MMU last year. He used a range of modelling methods to assess the long-term viability of black grouse populations in the face of changes to the Scottish uplands. The PhD was funded by Manchester Metropolitan University and the World PheasantAssociation. Matt is now a lecturer in Conservation Biology and Animal Behaviour at the University of Chester. Contact him at M.Geary@Chester.ac.uk. More information about his research is at http://mattgeary.github.com.