Simon Thirgood

Habitat loss and raptor predation: disentangling long- and short-term causes of red grouse declines.

The number of red grouse (Lagopus lagopus scoticus) shot in the UK has declined by 50% during the 20th century. This decline has coincided with reductions in the area of suitable habitat and recoveries in the populations of some avian predators. Here we use long–term records of shooting bags and a large–scale manipulation of raptor density to disentangle the effects of habitat loss and raptor predation on grouse populations. The numbers of grouse harvested on the Eskdale half of Langholm Moor in southern Scotland declined significantly during 1913–1990 and grouse bags from the whole moor from 1950 to 1990 exhibited an almost identical but non–significant trend. Hen harriers (Circus cyaneus) and peregrine falcons (Falco peregrinus) were absent or bred at low densities on this moor throughout this period but heather–dominant vegetation declined by 48% between 1948 and 1988. Harrier and peregrine breeding numbers on Langholm Moor increased to high levels following protection in 1990 whilst grouse density and grouse bags declined year after year until shooting was abandoned in 1998. The prediction of a peak in grouse bags on Langholm Moor in 1996 based on the patterns of bags during 1950–1990 was supported by the observed peaks in 1997 on two nearby moors with few raptors which formerly cycled in synchrony with Langholm Moor. This study demonstrates that, whilst long–term declines in grouse bags were most probably due to habitat loss, high levels of raptor predation subsequently limited the grouse population and suppressed a cycle. This study thus offers support to theoretical models which predict that generalist predators may suppress cycles in prey populations.

Hen harrier foraging success in relation to land use in Scotland

In the UK, hen harriers (Circus cyaneus) are illegally killed on moorland that is managed for red grouse (Lagopus lagopus scoticus), and they produce fewer young per female on grouse moorland than on either unmanaged moorland or forestry. However, those breeding attempts on grouse moorland that escape nest destruction produce more young than in other land-use classes. One explanation for this difference is that food is more available to harriers on managed moorland than elsewhere. To examine this hypothesis, we compared the capture rates of hunting male harriers on sites across Scotland. Four of these sites were managed for grouse whilst the remaining three consisted of either unmanaged moorland or a mixture of unmanaged moorland and young forestry plantations. We found a significant difference in capture rates, with harriers on managed grouse moorland capturing prey at a greater rate than elsewhere, supporting the idea that prey were more available on grouse moorland. However, there was no difference in strike rates between the land-use classes, suggesting that prey were not necessarily more abundant on grouse moors. Males on unmanaged moorland tended to catch larger prey, though this was insufficient to compensate fully for the reduced capture rates. The improved hunting success on grouse moorland means that this habitat is likely to be more attractive to breeding harriers, thereby increasing the conflict between those interested in maximizing grouse numbers and those interested in conserving rare raptors.

Could translocation aid hen harrier conservation in the UK

Translocation is increasingly used in conservation to re-establish orn augment populations of threatened species or to remove individualn animals from areas of human-wildlife conflict. We assess the feasibilityn and utility of translocating hen harriers ( Circus cyaneus ) in the UK ton enhance their distribution and abundance whilst simultaneously reducingn the impact of harrier predation on red grouse ( Lagopus lagopus scoticus )n populations and shooting bags. Current knowledge of hen harrier feedingn ecology, dispersal, survival and recruitment suggests that they would ben suitable subjects for translocation with the aim of increasing theirn distribution in the UK. Assessment of habitat and food availabilityn suggest that there are suitable recipient sites beyond the currentn range of the hen harrier in the UK. However, translocation would notn be a sustainable method of reducing predation on grouse moors becausen it would have to continue indefinitely as long as grouse moorsn attracted harriers. Translocation of harriers to grouse moors where theyn have been locally extirpated would not be appropriate until levels ofn illegal control are reduced. Establishing new harrier populations throughn translocation away from grouse moors may become desirable if initiativesn to reduce human-raptor conflicts on grouse moors are unsuccessful, or asn an interim measure to accelerate the recovery of hen harriers in then UK.

Efficacy of acaricidal tags and pour-on as prophylaxis against ticks and louping-ill in red grouse.

Abstract This paper examines the efficacy of 10% lambdacyhalothrin‐impregnated plastic tags and a deltamethrin pour‐on preparation in protecting red grouse chicks from parasitism by ticks and subsequent infection with the louping‐ill virus. In 1995, ten red grouse hens (Lagopus lagopus scoticus) in a free‐living population in north‐east Scotland were fitted with lambdacyhalothrin‐impregnated plastic tags, glued to radio transmitters. Chicks of more than 10 days of age from a further ten untreated radio‐collared hens were caught and fitted with individual tags to the plagium. Both treatments significantly reduced tick burdens in the short term. The number of larvae and nymphs on chicks up to 45 days was less under both treatments than on control chicks and tagged chicks had fewer nymphs than chicks from treated hens. Nevertheless, treatments did not reduce viral infection rates nor increase survival to 10 weeks, possibly explained by incomplete treatment of tagged broods and/or direct or indirect mortality due to tags. In 1996 chicks in ten broods from hens with radio transmitters were individually treated at 14 days of age at a rate of lmg/kg of chick with a deltamethrin pour‐on preparation. This preparation significantly reduced the number of larvae and nymphs on grouse chicks 7–10 days after application below the number on untreated controls. At 20 days from application, however, only larval numbers were lower on treated chicks. Nevertheless louping‐ill virus infection prevalences were significantly reduced at 35 days of age and survival of chicks to 10 weeks increased.