Population responses of Red Grouse Lagopus lagopus scotica to expansion of heather Calluna vulgaris cover on a Scottish grouse moor

Abstract

Loss of heather Calluna vulgaris-dominated moorland in Britain has been associated with long-term declines in Red Grouse Lagopus lagopus scotica, a gamebird of economic importance. We tested whether restoring heather habitat on a grouse moor in southwest Scotland, where heather was previously in decline, improved Red Grouse density, productivity, and survival. We analyzed spatial and temporal relationships between Red Grouse demographic rates, estimated from counts, and habitat variables measured from ground and aerial vegetation surveys. Reductions in sheep Ovis aries grazing and other heather restoration measures (i.e. burning and cutting, and in some areas reseeding of heather following herbicide treatment to reduce grass dominance) increased total heather cover by 10% and the area of heather-dominated vegetation by 30% within six years. Prebreeding, and for aerial surveys also postbreeding, densities of Red Grouse were highest in areas with more heather cover (range: 0-92%), and prebreeding densities increased more where heather recovery was greatest. However, we found no relationship between heather cover and Red Grouse productivity or survival rates, the latter also when rates were estimated from radio-tagged individuals. Changes in heather cover were not associated with changes in postbreeding densities or survival of Red Grouse, although they were positively related to change in productivity for aerial surveys. Overall, management for Red Grouse had a larger effect on density and productivity than reductions in sheep grazing. This is the first study examining Red Grouse responses in relation to changes in heather cover within the same site, in contrast to previous between-moor comparisons, where other factors may have contributed to variation in Red Grouse demography. Our results suggest that, in the long term, heather restoration has the potential to increase Red Grouse carrying capacity, but realizing this potential first requires improving Red Grouse demographic rates. Population responses of Red Grouse Lagopus lagopus scotica to expansion of heather Calluna vulgaris cover on a Scottish grouse moor RÉSUMÉ. La perte de terrains marécageux dominés par la bruyère Calluna vulgaris en Grande-Bretagne a été associée à la baisse de longue date du Lagopède d'Écosse Lagopus lagopus scotica, un oiseau gibier d'importance économique. Nous avons testé si la restauration d'habitat de bruyères sur un terrain marécageux utilisé par les lagopèdes dans le sud-ouest de l'Écosse-où la bruyère était auparavant en diminution-améliorait la densité, la productivité et la survie du Lagopède d'Écosse. Nous avons analysé les relations spatiales et temporelles entre les paramètres démographiques du lagopède, estimés à partir de dénombrements, et les variables d'habitat mesurées au moyen de relevés de végétation terrestres et aériens. La réduction du broutement par le mouton Ovis aries et les autres mesures de restauration de la bruyère (c.-à-d. le brûlage et la coupe, et dans certains endroits le réensemencement de bruyères suiv...

Fluctuations in field vole abundance indirectly influence red grouse productivity via a shared predator guild

“…The 115-km 2 site was dominated by a heterogeneous mosaic of heather and grass moorland ( Fig. 1), which was surrounded by acid grassland (where heather previously dominated but had been lost through overgrazing by sheep, Thirgood et al 2000b), interspersed with wooded stream gullies, agriculturally-improved grassland and patches of commercial coniferous forest and mixed deciduous woodland (Ludwig et al 2018a).…”

“…Simultaneously, the moor was used for sheep farming, which became the primary land-use between 2000 and 2007, when the moor was not managed for grouse (Baines et al 2008). Following five decades of heavy sheep grazing, which converted almost half of the heather moorland to acid grassland (Thirgood et al 2000b), sheep grazing ceased in 2011 on 39 km 2 of moorland to facilitate heather restoration (Ludwig et al 2018a).…”

Long-term changes in the abundance and breeding success of raptors and ravens in periods of varying management of a Scottish grouse moor

“…Given the nonexperimental design of this study, it was not possible to fully disentangle the potentially confounding effects of the different management components such as predator control, habitat management, or diversionary feeding, which may not only influence raptors directly but also indirectly via their prey species. However, grouse moor management had no apparent effect on passerine or vole abundance at Langholm, and differences in Red Grouse abundance between management periods were largely explained by predator control because neither breeding success nor survival were related with habitat management or heather cover (Ludwig et al 2018a). Our data on management-related differences in predator indices and causes of breeding failures suggest that predator removal by gamekeepers may have been the main process influencing breeding success of Hen Harrier and Merlin.…”

“…Some studies also suggest that heather burning, which has increased in frequency on many grouse moors in England during the last decades (Yallop et al 2006, Robertson et al 2017, may reduce the availability of old heather stands preferred for nesting by both Hen Harrier and Merlin (Ewing et al 2011, Heavisides et al 2017 and of passerine prey such as Meadow Pipits (Smith et al 2001, Pearce-Higgins andGrant 2006). However, at Langholm, where heather burning was resumed in 2008, the average heather height did not change between 2007, prior to the restoration of management, and 2015 (Ludwig et al 2018a), suggesting that the amount of tall heather was not limiting nest site availability to either species. Furthermore, potential negative effects of heather management on Meadow Pipit breeding abundance may be balanced by increases in their breeding success, together with increases of other prey such as Red Grouse and waders following predator control (Fletcher et al 2010).…”

“…When managed for Red Grouse, gamekeepers legally controlled generalist predators on the whole 115-km² site and managed the heather habitat by rotational burning or cutting more mature stands of heather to provide a mosaic of heather height and structures that may benefit breeding Red Grouse (Robertson et al 2017, Ludwig et al 2018a. Predator control was carried out throughout the year.…”