The consultant, the newt trap and the water shrew
8th December 2009, TuesdayBecause great crested newts are a protected species developers are required to undertake surveys of ponds before proposing development on or near them. The intention is to determine if this amphibian is present, and then recommend mitigation to prevent damage to the newt population. The survey is usually undertaken by an independent ecological consultant holding a licence to disturb newts. Natural England, who are responsible for licensing such work, require that effective survey methods are used to determine if newts are likely to be present.
One of the best ways to confirm if newts are present in a pond is the bottle trap, made by cutting off the cone top of a squash bottle and inverting it into the bottom half of the bottle. All very Heath-Robinson, but a surprisingly effective way of determining the presence of this species, so much so that if you do not use traps you will be asked to justify their ommision when your report is delivered.
So far so good, but there is a problem. Unfortunately bottle traps are also very effective at capturing and drowning water shrews.
So, we have a situation where it is actually illegal to trap shrews in case you kill them, but legislation that protects the newt requires bottle trap surveys. Having checked with Natural England after I captured my first water shrew I was told to continue trapping and review the situation if I captured any more. This prompted some thought on alternative, safer traps, and the design that I have ended up using appears at first sight counter-intuitive. The trap is made in the same way, but has an escape hole cut at it’s end, located just above the water surface. This not only provides air for the newts, but is intended as an escape route for any captured shrews. This is on the assumption that water shrews swim with part of their body above the water surface and will therefore find it easier to escape than a newt below the water surface.
The results over the past two survey seasons have been pleasing. In 874 tests, comparing old and new traps in paired trials, we have drowned no water shrews in the new traps, and they seem to be only slightly less effective at capturing great crested newt. I am trialing the traps in pairs and comparing the results, with the intention of gathering a large data set to determine how less efficient they are. At the moment they appear to be almost as good a way to capture smooth newts, whereas you capture approximately 75% of the number of great crested newt you might expect in a conventional trap. In a pond where there is a risk of drowning water shrews it has to be preferable to use more modified traps, rather than drown these mammals. I need a larger data set for great crested newt and palmate newts to confirm how effective they are, so if any consultants out there are interested in helping me test these new traps this spring I would be delighted to hear from you - please use this link to get a contact e-mail address.