Predation Control Studies

Failure to address many of the difficulties inherent in the analysis of carnivore faeces has hitherto limited the value of this technique in comparing carnivore diets or quantifying carnivore food consumption. In this review, major problems are discussed, and improved procedures designed to overcome them are recommended.The principal improvements recommended for laboratory procedures address the microscopic fraction of faeces, which cannot be analysed visually. This fraction may be derived from a variety of sources, leading to bias in previous techniques, particularly with regard to the importance of earthworms and birds. Attention to the microscopic fraction is necessary for correct comparison or quantitative determination of diet.Particular attention is given to statistical procedures which quantify the errors that arise in collection of samples, or during analysis. Clear statement of such errors will lead to greater comparability between studies. The procedures recommended here define the limits to accuracy in relation to sample size, total faecal production, and laboratory methods. In conjunction with adequate pilot studies, these techniques will allow more effective design of ecological studies relating to carnivore diet and food consumption.

1. Foxes Vulpes vulpes probably did not occur naturally on the Isle of Man, but were present in small numbers in the mid 19th century. They were introduced again in the 1980s, and in 1990 the population was estimated at 120-300 individuals (20-50 per 100 km 2 ) on the basis of field signs. We used a nocturnal spotlight transect survey technique to assess the status of foxes on the Isle of Man in September 1999. This method had previously been used effectively to estimate fox densities in populations as sparse as 16 per 100 km 2 . We surveyed a total of 852 km over a period of eight consecutive nights, during weather conditions which allowed excellent visibility. No foxes were seen. 2. By comparison with equivalent survey efforts in reference areas of mainland Britain, we conclude that post-breeding fox density on the Isle of Man was certainly below 2.5 per 100 km 2 , implying a maximum of 15 foxes on the entire island. We estimate a probability of only 15-25% that a fox population of 1 per 100 km 2 was present but not detected; this would be equivalent to only five or six individuals on the whole island. Foxes may even be entirely absent, although unsubstantiated sightings continue to be reported. 3. This finding is significant in understanding the ecology of the Isle of Man, and in planning the conservation of a number of ground-nesting bird species there, as well as for farming interests, and for contingency planning against an accidental introduction of rabies.

SUMMARY 1. In the UK the population of Mute swans (Cygnus olor) has doubled since the early 1980s. Swans feed mainly on submerged aquatic macrophytes, especially water crowfoots (Ranunculus spp. subgenus Batrachium). The River Avon (a chalk-stream in southern England) is designated a Special Area of Conservation, in which Ranunculus-dominated habitat is required to be protected. This study focused on the River Wylye (part of the Avon catchment) to quantify the impact of grazing by swans on the biomass of ...

The introduction of American mink (Neovison vison; hereafter mink) into Europe has had severe impacts on many native wildlife species, including the water vole (Arvicola amphibius) in mainland Britain. Although trapping has been widely used to attempt to control mink, managers have little direct evidence of its effect on mink density or distribution, particularly where immigration of mink from nearby areas is inevitable. Such evidence is needed to justify the use of lethal methods in conservation policy. During 2006-2010 we removed mink from the River Monnow Catchment in western Britain, using track-recording rafts to monitor continuously for mink presence, guiding a strategic trapping effort. The area monitored and trapped was increased in stages, from a core sub-catchment with 109 km of water-course in 2006, to a 421km 2 catchment with 203 km of water-course in 2009. In each successive sub-catchment, mink detection and capture rates declined rapidly to near-zero levels after trapping began. Detections and captures showed seasonal peaks in every year corresponding to known dispersal periods, but also declined steadily from year to year, with increasing periods in which we did not detect mink. These results suggested that each subcatchment was cleared of mink within a few months, with subsequent captures attributable to immigration. On average, we detected each mink 5.1 times before capture (daily probability of detection ¼ 0.059 per mink and raft), and trapped them 3.4 days after deploying traps in response. On average, mink entering the area were likely to have been present for less than 13 days before capture. Water voles had been extinct in the Monnow Catchment since the 1980s. During 2006-2008 (starting 6 months after mink trapping commenced), we released 700 captive-bred water voles into the treatment area to re-establish a wild population. Persistence of this population through the 4 years of the project was considered indicative of effective mink control. This study demonstrates that, even in a mainland context, a systematic trapping strategy can have a substantial impact on the density and distribution of a damaging species, in this case allowing the restoration of a native prey species. ß 2013 The Wildlife Society

We developed and tested physical excluders to prevent non-target animals from entering tunnels containing spring traps intended to kill a range of small (<2 kg) mammalian pest species. In ®eld trials over 82,954 trap-nights, excluders did not signi®cantly decrease stoat (Mustela erminea) or weasel (Mustela nivalis) capture rates, but did substantially reduce the capture rate of larger target species, notably grey squirrels (Sciurus carolinensis) and rats (Rattus norvegicus). Excluders virtually eliminated capture of hedgehogs (Erinaceus europaeus) -a legally protected species. By inference, larger protected species (polecat Mustela putorius, pine marten Martes Martes, otter Lutra lutra and wild cat Felis sylvestris) would be excluded, as would mink (Mustela vison), a legitimate target species. These excluders should be advocated where there is a real risk of catching protected species. However, because excluders compromise utility, we recommend that their use should remain discretional unless clearly preferable alternative methods to manage target pest species are developed. #

We developed and tested physical excluders to prevent non-target animals from entering tunnels containing spring traps intended to kill a range of small (<2 kg) mammalian pest species. In ®eld trials over 82,954 trap-nights, excluders did not signi®cantly decrease stoat (Mustela erminea) or weasel (Mustela nivalis) capture rates, but did substantially reduce the capture rate of larger target species, notably grey squirrels (Sciurus carolinensis) and rats (Rattus norvegicus). Excluders virtually eliminated capture of hedgehogs (Erinaceus europaeus) -a legally protected species. By inference, larger protected species (polecat Mustela putorius, pine marten Martes Martes, otter Lutra lutra and wild cat Felis sylvestris) would be excluded, as would mink (Mustela vison), a legitimate target species. These excluders should be advocated where there is a real risk of catching protected species. However, because excluders compromise utility, we recommend that their use should remain discretional unless clearly preferable alternative methods to manage target pest species are developed. #