Designing the perfect fox snare

Key achievements

• Developed the design for effective break-away snares to allow non-target animals to break free.
• Achieved high capture rates compared with averages from gamekeepers.
• Developed the design for a cushioning spring to avoid injuring the caught animal.
• We are close to having a new, more humane snare ready for field-testing.

In fox snaring, performance (target capture rate, non-target involvement, and the welfare of captured animals) is chiefly dependent on operator skills and practices. As such, the Independent Working Group on Snares addressed these with its Code of Practice. However, snare design also makes a difference.

Although there have been attempts in the past to improve snares in various ways, new designs were only attractive to operators if they promised better catching ability. Now, however, the IWG Report and the Animal Welfare Bill place responsibility for welfare of the captured animal morally and legally (respectively) on the shoulders of the operator. One recommendation of the IWG was to explore any modifications to the snare that might conceivably reduce non-target captures and lessen the risk and severity of injuries for captured animals. There are two main concepts, neither of them new:

1. Break-away devices, which release species stronger than the target species by building a weak link into the snare.
2. Cushioning springs, which dampen the physical strain incurred by captured animals when struggling against the snare.

The keys to successful development of such devices must be accurate specification, and correspondingly precise manufacture. With break-away snares, for example, the aims are to release non-target species such as badgers and deer easily, and to retain foxes reliably. The distinction between target and non-target species is unlikely to be clear cut. Some species may challenge the snare with a steady pull, others with stronger but briefer lunges. There are big foxes and small badgers. Even among members of a species, the pull exerted by different individuals varies not only with size and build, but also with motivation. Any specification is therefore likely to compromise one aim or another. However, once the optimum specification has been chosen, it needs to be consistently achieved. The finished product must be dependable, not a lottery.

It is hard to add anything to a snare without destroying its essential minimalist nature. For this reason too, it is important to have high quality components that are dependably strong while also simple, small and discrete. In our research, we are indebted to DB Design for advising us and supplying suitable components.

Developing the break-away specification (see Figure 1) has been a steady but frustrating process. Prototype snares are necessarily hand-made. At each change of specification, an adequate number of snares had to be prepared for use, but the entire batch could be consigned to the rubbish bin by a capture on the first night of deployment. We began these cycles of development using break-away snares at the 'weak' end of the spectrum. From a research viewpoint it was important to know which species broke free and which were restrained, so we also had to devise a way of retaining the animal in the snare even though the break-away device had released it. This added yet more components. Despite these handicaps, we achieved high capture rates (27.5 foxes per thousand snare-days, or 38 snare-days per fox) compared with average figures from gamekeepers (1.1 and 3.5 foxes per thousand snare-days in two previous studies).

Figure 1. The break-away snare, showing the component parts

Developing a cushioning spring has to follow the specification of the break-away device. The only way to assess its benefit would be to compare the condition of samples of foxes taken in normal practice using snares with and without springs. Because foxes are variable in size, strength and motivation, quite large samples would be necessary, and because it is a big investment even to organise such a trial among gamekeepers, we need to make a very close guess at the correct specification for the spring. A spring that is either too weak or too strong will be inoperative for much of the time, so the ideal may be one that is progressive in action. However, we can also foresee a complex relationship with the break-away device. The break-away snare can open predictably only if pulled against a dead weight, so spring strength must be chosen so that it is inoperative under the strong pulls exerted by large non-target animals.

We believe we are close to a final design that will be ready for widespread field testing late in 2006.