How to use a Larsen trap correctly and effectively

A Larsen trap is an extremely visible form of pest control but using one needs be done correctly. A passer-by who spots a dirty Larsen trap with a dejected-looking calling bird (decoy), standing on a heap of splattered droppings and flyblown carcass remains is not going to come away with a good impression of gamekeeping.

The reason for using a Larsen trap

The main aim to to prevent corvids predating wild game nests. The hope is that other vulnerable species, such as lapwings, curlews, blackbirds and song thrushes, will benefit too.

How a Larsen trap works

A Larsen trap trades on a bird’s territorial instincts. A corvid gets caught because it wants to drive the calling bird in the trap away. (Read how to catch a call bird.)

Crows and magpies start to get seriously territorial in late March, at much the same time as the first game eggs are beginning to appear. So this is the time to start with a Larsen trap, for it is the eggs that are most vulnerable. Once the game chicks have hatched and are away with their parents, they are much less vulnerable.

If you make an early start you do not allow the corvids to get too underway with their nesting season. I start with Larsens in late March and April, with crow and magpie decoys. By deploying my first captives in extra traps, I can soon have several running within a week and my aim is 
to remove the territorial pairs of both species by early April. From then on, 
it is just incomers that I am after.

This strategy also has a view to the welfare of the corvids themselves. By removing pairs before they start nesting and taking out incomers, I am making sure that there are no orphaned chicks. Breeding pairs from over the boundary will not abandon a nesting attempt — it is the non-breeding “lower orders” that are looking for vacant territories to colonise. You never know where a new colonist 
will turn up, so do not leave your trap 
in the same place for long.

Better results generally come from being mobile. I rarely leave a Larsen trap in 
the same place for more than two days. 
By then, if I have not caught, I am probably not going to, at least for the moment.

Choice of trap

The original Larsen trap, as invented by Danish gamekeeper Mr Larsen, had a wooden frame with wire netting. However, things have progressed and these days I much prefer an all-weldmesh version.  The all-weldmesh design has several other advantages, not least being that it is more robust than a wooden-framed model, so it is less prone to both accidental damage and vandalism. The lack of an obvious wooden frame makes 
it more difficult to spot from a distance 
too, so it is less likely to be investigated 
by trespassers.

Decoy welfare

The general licences that allow us to use Larsens have different wording between England, Wales, Scotland and Northern Ireland, but they all impose the same basic welfare criteria and you are legally obliged to follow the terms and conditions. In particular, you must supply appropriate food, water at all times, a decent perch and adequate shelter from adverse weather.

I always site my trap in the lee of 
a hedge or large tree, to supplement the roof shelter that is built in. I use rabbit drinkers from pet shops for water. They keep the water clean and healthy, and avoid the risk of bowls being tipped over and birds defecating in their water. The 600ml size is best, as it is less likely to be dislodged from the side of the trap than the smaller one.

For food, I fix a bowl to the side of the trap and use complete diet dog food kibble, soaked with extra water. This is clean, easy to use and provides balanced nutrition for birds whose natural diet is similar to the needs of a dog. It is also less likely to attract the attention of scavengers compared with bits of carcass — I have never had to evict 
a buzzard from a trap fed with dog food.

The soaked kibbles seem perfectly palatable to the birds, and it is much easier to keep the trap clean compared with the inevitable mess that comes from feeding bits of rabbit or other carcass.

Attracting the right birds

Minimising capture of non-targets is also a key objective. Part of this comes from siting the traps in places that have worked well in the past. As with so much wildlife, what makes a good crow or magpie territory seems to be written in the local geography. Another key objective is not to make the trap attractive to non-target species.

Check regimes

You are legally obliged to physically check your Larsen every day at intervals of not more than 24 hours. In practice this means that you need to check more often, because you cannot afford to be even a few minutes late. I usually go twice a day, but I try to site my Larsens where I can spy on them from a distance. In this way, if there is a bird about to get caught and my 24 hours are not up, I can leave the situation to develop.

When removing captives, I always 
wear gardening gloves to give me confidence and avoid being pecked. People have died of septicaemia from corvid bites, so be careful. It also means that I can grab the bird quickly and rap its head hard on the first available suitable object. This should kill it outright, but I always break the neck too, just to be sure.

Signs on Traps

I carry out my Larsen trapping as humanely as possible as part of a serious game and wildlife conservation package and I find that most sensible people are won over, even if they were sceptical. I also put signs on my traps to explain this, so that even trespassers can begin to understand.

Questions about Larsen traps

Q: Can you explain why I have little success with my Larsen traps in the autumn and winter? I have one with a magpie and the other with a crow on my smallholding. There are plenty of magpies and crows in the area, but they seem reluctant to be caught. 

A: Carrions and magpies become communal birds in the autumn and winter, and crows, in particular, may be seen in large communal roosts. In February, dominant crows break away from the community to pair up and defend a territory. It is worth remembering that the major predator of crows’eggs and young is other crows. The best results with a Larsen trap will be achieved when the trap is placed within the territory of a pair of crows or magpies as they will then try to attack and drive off the call bird.

Though the spring catching period is not exclusive, it is the most productive time.

Q: Will a non-local bird in my Larsen trap attrack more crows? This past spring I caught no fewer than 35 carrion crows in a single Larsen trap. In previous years the totals for this same trap have only been in single figures. I can’t explain the increase, but one factor may be significant. My decoy bird came from a friend who lives 80 miles away, whereas in previous years I’ve employed locally caught birds. Do you think this strange bird on the patch could have made any difference?

A: Our carrion crow population is divided into territory-holding pairs and non-breeders. Territorial birds are dominant, with the males in turn dominant over the females.

Studies have shown the boundaries of a pair’s territory are most vigorously defended against unknown intruders, while familiar individuals from the adjoining territory are more likely to be tolerated. This has the advantage of mutual defence against non-territory holders on the borders.

Thus it follows that a decoy bird brought in from some distance away is more likely to excite the residents than a local bird. Given a choice of decoy bird I would always opt for the bird caught as far away as possible from the area in which I was trapping.

Q: Are we allowed to use Larsen traps this year? I have heard different things about general licences covering England and the use of these traps, but no one really seems to know what’s going on and if we are allowed to use them.

In England, general licences have been extended from 1 March until 
1 August 2020. This includes the use 
of Larsen traps. You don’t need to do anything different from last year as long 
as you act as per the licence conditions — with two exceptions: if you intend to control wild birds within 300m of a protected site such as a Site of Special Scientific Interest, or you intend to control lesser black-backed or herring gulls. For these you will need to apply for and be granted an individual licence. The people who applied for individual licences last year should have already been contacted. Visit Gov UK for full details of the licences.