David Newborn

Do parasites make prey vulnerable to predation? Red grouse and parasites

An extensive post-mortem survey of grouse revealed that birds killed by predators in spring and summer had significantly greater burdens of the caecal nematode Trichostrongylus tenuis than grouse shot during the autumn. Furthermore, grouse that appeared to have died through the effects of parasites carried greater worm burdens than grouse killed by predators. The proportion of grouse with high levels of parasite infection increased with the intensity of predator control as measured indirectly through keeper density. These two empirical observations suggest that predators selectively prey on heavily infected grouse. The interactions between parasites and predators were examined experimentally by reducing the worm burdens of female grouse with an oral anthelmintic

Regulation and stability of a free-living host - parasite system : Trichostrongylus tenuis in red grouse. I : Monitoring and parasite reduction experiments

Intensive population studies were conducted for 10 years on red grouse (Lagopus lagopus scoticus) and the parasitic nematode, Trichostrongylus tenuis, in northern England. Winter loss was the key factor determining changes in grouse numbers, although breeding losses were also important. T. tenuis had an aggregated distribution within the adult grouse population, even though the degree of aggregation was relatively low compared with other parasite systems

Factors affecting unintentional harvesting selectivity in a monomorphic species

1. Changes in the abundance of populations have always perplexed ecologists but long-term studies are revealing new insights into population dynamic processes. Long-term data are often derived from harvest records although many wild populations face high harvesting pressures leading to overharvesting and extinction. Additionally, harvest records used to describe population processes such as fluctuations in abundance and reproductive success often assume a random off-take. 2. Selective harvesting based on phenotypic characteristics occurs in many species (e.g. trophy hunting, fisheries) and has important implications for population dynamics, conservation and management. 3. In species with no marked morphological differences between the age and sex classes, such as the red grouse Lagopus lagopus scoticus during the shooting season, hunters cannot consciously select for a specific sex or age class during the shooting process but harvest records could still give a biased reflection of the population structure because of differences in behaviour between age and sex classes. 4. This study compared age and sex ratios in the bag with those in the population before shooting for red grouse at different points in the shooting season and different densities, which has rarely been tested before. 5. More young than old grouse were shot at large bag sizes and vice versa for small bag sizes than would be expected from the population composition before shooting. The susceptibility of old males to shooting compared to females increased with bag size and was high at the first time the area was shot but decreased with the number of times an area was harvested. 6. These findings stress that the assumption made in many studies that harvest records reflect the age and sex ratio of the population and therefore reflect productivity can be misleading. 7. In this paper, as in the literature, it is also shown that number of grouse shot reflects grouse density and therefore that hunting selectivity might influence population dynamics in a cyclic species. 8. The study is not only relevant for red grouse but applies to systems showing interactions between selective harvesting and wider ecological processes, such as age- and sex-related parasitism and territoriality, which may drive population fluctuations.

Brood defence in a precocial species: variations in the distraction displays of red grouse, Lagopus lagopus scoticus

Abstract Large temporal and spatial variations in both the frequency (percentage of birds) and intensity of distraction displays performed by red grouse were examined in relation to four hypotheses. First, that the display is performed in response to the risk of brood predation was supported by an increase in the frequency of high-risk distraction display with predator pressure, brood size and poor cover (for males but not females) although females disturbed when brooding were not more likely to display than females not brooding. Second, that the frequency of display depends on the predation risk on the parents was supported by a lower level of display by females whose mate was absent and a significant correlation between the levels of display of members of a pair. Third, that the condition of the parent bird influences the frequency of display was refuted since distraction displays in females with reduced parasite burdens and hence improved body condition did not display more than parasitized females. Fourth, that the frequency of display is related to the costs of replacing a brood was not supported since there was no association between frequency of display and either clutch size or brood age. The adaptive value of the large variation in the frequency of brood defence is discussed in relation to predator naivety.

Numbers and distribution of Black Grouse Tetrao tetrix males in England: results from the fourth survey in 2014

Capsule A survey in 2014 of male Black Grouse in England showed a continuation of declines in North Northumberland and increases in the North Pennines and Yorkshire Dales. Aims To survey the abundance and range of Black Grouse males in northern England. Methods Males attending leks were surveyed in spring 2014 and numbers compared with previous surveys in 1998, 2002 and 2006. Results Abundance increased from 773 males in 1998 to 1437 in 2014 and range from 74 occupied 5 × 5-km grid squares in 1998 to 108 in 2014. Conclusion Whilst numbers and range of Black Grouse in England have increased overall, the species has practically disappeared from North Northumberland, causing a 34 km gap to develop in the range, potentially preventing interchange between the English and Scottish populations.

No Evidence for Resistance to Fenbendazole in Trichostrongylus tenuis, a Nematode Parasite of the Red Grouse

Abstract The parasitic nematode Trichostrongylus tenuis has a detrimental effect on red grouse (Lagopus lagopus scoticus) at the individual and population levels. Treatment using grit coated with the anthelmintic fenbendazole hydrochloride reduces parasite infection and increases grouse density. However, a frequent and low dose of anthelmintic increases selection pressure for parasite resistance, a serious practical and economic problem. We used an egg hatch assay to test resistance of T. tenuis from 12 moors in northern England, which differed in grit treatment intensity. The anthelmintic concentration that prevented 50% and 95% of T. tenuis eggs from hatching (ED50 and ED95, respectively) did not differ among moors and were not related to treatment. We suggest annual monitoring and responsible anthelmintic use to prevent resistance so that medicated grit continues to enhance red grouse management.

Does rotational heather burning increase red grouse abundance and breeding success on moors in northern England

Rotational burning of moorland vegetation is considered by grouse moor managers to create structurally diverse habitat that helps maximise red grouse Lagopus lagopus scotica (Lath.) abundance for shooting by increasing breeding success and adult survival. However, there is growing concern that increasing levels of burning, particularly on deep peat, are impacting upon upland ecosystems. We used linear mixed models to examine the influence of burning on heather Calluna vulgaris (L.) height and structure, and on grouse density and breeding success, at 36 moors in northern England which practiced driven grouse shooting and employed full-time gamekeepers to burn heather, but also to control generalist predators of grouse and their parasitic nematode worms. Variation in heather height was positively associated with burning extent on moors and the relationship between heather height and burning was similar on moors of deep (blanket bog) and shallow peat (heath). Grouse pre-breeding density was not related to burning extent, but breeding success and post-breeding density were positively associated with extent of burning on moors. Relationships between grouse and burning were similar on heath and blanket bog. Higher grouse breeding success and post-breeding density were likely to be associated with a more varied vegetation structure following burning. Rotational burning is associated with higher grouse breeding success and post-breeding densities beneficial for driven grouse shooting. Thus a conflict may exist between rotational burning to benefit grouse and potential impacts of burning on ecosystem services such as carbon storage and flood protection. Potential benefits of burning for increasing grouse breeding success and post-breeding density need to be considered carefully against any likely impacts on ecosystem services, particularly in areas of blanket peat.