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

Abstract

Management of heather moorland for driven Red Grouse (Lagopus lagopus scotica) shooting in the British uplands may benefit some raptors by reducing predation risk, especially when breeding, and by increasing food availability. We describe changes in abundance and breeding success of four raptor species and Common Raven (Corvus corax) during a 27-year study on a grouse moor in southwest Scotland in relation to whether or not the moor was managed by gamekeepers. Ground-nesting raptors, Hen Harrier (Circus cyaneus) and Merlin (Falco columbarius), increased during periods of grouse moor management and had a higher proportion of successful nesting attempts. Predation was the main apparent cause of breeding failure. In contrast, grouse moor management did not influence either abundance or breeding success of tree-and crag-nesting species, i.e., Peregrine (Falco peregrinus), Common Buzzard (Buteo buteo), and Raven. Buzzard sightings increased during the study, in line with their national recovery, whereas Peregrine and Raven showed little change in abundance. The results of our study highlight that management for Red Grouse can benefit both Hen Harrier and Merlin. However, on a UK scale these benefits to Hen Harriers, but not Merlin, are outweighed by their illegal killing, caused by fears that their consumption of Red Grouse can undermine the economics of grouse moor management. Busard Saint-Martin et au Faucon émerillon. Toutefois, à l'échelle du Royaume-Uni, ces avantages pour le busard, mais pas pour le Faucon émerillon, sont contrebalancés par son abattage illégal, causé par la crainte que leur consommation de lagopèdes puisse compromettre le marché économique de la gestion de la lande pour les lagopèdes.

Drivers of change in mountain and upland bird populations in Europe

“…This practice can be beneficial for ground‐nesting species such as grouse and waders on uplands, but at the expense of other predators such as mammals or corvids (Ludwig et al . 2020) and can be associated with the illegal persecution of raptors (see above).…”

“…Hunting had the highest magnitude effect size of all drivers, and included both legal hunting activity, which mainly consisted of grouse shooting on managed moorland in the UK (e.g. Ludwig et al 2020) or in boreal forests in Fennoscandia (e.g. Lampila et al 2011), and illegal persecution of protected species, such as vultures in southern Europe (e.g.…”

Retrospective comparisons of competing demographic models give clarity from “messy” management on a Scottish grouse moor

“…We used numbers of female hen harriers that successfully bred at Langholm (Ludwig, Roos, Rollie, & Baines, 2020) when modeling grouse productivity, because hen harriers commonly feed grouse chicks to their young, unlike peregrines. Redpath and Thirgood (1997) calculated grouse productivity at Langholm with and without harriers in 1995 and 1996; we applied their approach to their 1993–1994 data and derived a logistic relationship linking the proportional decrease in grouse productivity L P HH occasioned by harriers to the number HH of successful harrier nests: $$$$ {L}_{\mathrm{HH}}^P=\frac{0.2986}{1+{e}^{0.830\left(\mathrm{HH}-4.755\right)}} $$$$ Predicted decrease in grouse productivity, L HH , ranged from 0 when there were no hen harriers to 0.30 when the number of successfully breeding hen harriers exceeded 15 (Figure 2c).…”

“…The density‐dependent relationship for $$$ {S}_{w, dd} $$$ incorporated the effects of peregrines and hen harriers present over winter at Langholm. Breeding peregrine numbers at Langholm remained low throughout the study (Ludwig, Roos, Rollie, & Baines, 2020), wintering hen harrier numbers were unrelated to breeding numbers, and many wintered elsewhere (Ludwig, Roos, Rollie, & Baines, 2020; Redpath & Thirgood, 1997). Therefore, for the predictive model (Equation ) we assumed that $$$ {S}_w={S}_{w,\mathrm{dd}} $$$ remains the same in the presence of hen harriers, while $$$ {S}_s^{\mathrm{ad}} $$$ in Equation () took the same value as in the equivalent harrier summer model (Equation ).…”

“…Numbers of buzzard nests were not monitored consistently, so we used buzzard survey data based on sightings during breeding-bird transect surveys (Ludwig, Roos, Rollie, & Baines, 2020). Because the index of buzzard abundance thus obtained varied highly from year to year, we described the local buzzard population as low in years with a 5-year moving average of sightings/km below 0.10 (1992-1999), moderate at 0.10-0.15 (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007), and high above 0.15 (2008-2019; Figure 1).…”