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Rat control 2: minimising risk to wildlife

Course: Rat control | Last Updates: 7th October 2015

Dr. Alan Buckle
Biography >>

Effective, but also safe and responsible control is essential because residues of anticoagulant rodenticides, which are widely used for rodent control, are increasingly found in wildlife.

That is why the industry has come together to devise the Campaign for Responsible Rodenticide Use (CRRU) to minimise the risk to wildlife.

Drawing on the knowledge of industry experts, Natural England, the Health & Safety Executive and the Universities of Huddersfield and Reading, it has developed a seven-point code, which is being promoted under the Think Wildlife banner.

1. Have a planned approach

Rodenticide use should be properly planned and managed just like any other agrochemical input. A few hours spent at the start will save days at the end.

rat-and-bird-of-prey A thorough survey of the infested site is essential to determine the distribution of the rat infestation, where baits can be put out safely and what risks there are to non-target animals.

During the survey it is necessary to look around the site and try to put any foods the rodents are eating out of reach. This will promote good bait uptake and get the treatment completed more quickly. Note any areas that could be "rodent-proofed" and tidied once the control programme is completed.

But this shouldn't be done before the bait application because major changes in the environment may put rodents off taking the bait and displace them to areas where they are harder to find.

Rodenticide baits should only be used for as long as is necessary to achieve satisfactory control. In most cases control will be achieved within 35 days, fewer if infestations are small and bait takes are good.

If bait continues to be consumed without effect, a more potent anticoagulant should be considered. But if bait take is poor, relative to the apparent size of the infestation, consider re-siting the bait points and possibly changing to another bait base.

In this case particular attention must be paid to preventing the rodents' access to alternative foods.

2. Record the quantity of bait and where it is placed

Draw up a simple plan identifying areas of particular concern and keep on file. Record all bait points and the amount of bait laid during the treatment and then note rat activity at each bait point as the treatment progresses.

By carefully recording the sites of all bait points, responsible users of rodenticides are able to return to these sites at the end of the treatment and remove uneaten bait so that it does not become available to wildlife.

3. Use enough baiting points

Outright treatment failure, or unduly prolonged treatments, are often caused by not having enough bait points. It is important to follow strictly the label instructions regarding the size and frequency of bait points.

Advice on the frequency and number of visits to the site should also be followed.

If enough bait points are used the time taken for the control treatment is minimised, which reduces the risk of exposure to non-target animals.

4. Always collect and dispose of rodent bodies

The bodies of dead rodents may carry residues of rodenticides and, if eaten by predators or scavengers, are a source of wildlife exposure. Their disposal is one of the most important points on the CRRU code.

It is essential to carry out regular searches for rodent bodies, both during and after the treatment period. Bodies may be found for several days after rats have eaten the bait and rats may die up to 100m or more away from the baited site.

Remove any rodent bodies from the site and dispose of them using the methods recommended on the product label.

5. Never leave bait exposed to non-target species

Bait must be sufficiently protected to avoid accidentally poisoning other mammals and birds. This is the key to the CRRU "Think Wildlife" campaign.

Use natural materials, where possible, to protect baits from dust, rain and access by non-target species, but obviously leave an entrance clear for rodents.

Tamper-resistant bait stations are also available and offer the highest level of protection of baits from non-target animals and from human interference. Use these bait stations where it is suspected that covers made from other materials will not be secure enough to protect baits properly.

But note that wild small mammals, such as wood mice and voles, cannot be excluded from bait stations and it is by consuming these animals that most predatory birds are exposed to rodenticides.

6. Inspect bait regularly


Visit the site as frequently as the recommendations on the product label specify and replenish baits as necessary. Check bait points for disturbance by non-target animals.

Search the site for dead rodent bodies and remove, and safely dispose of, any spilled bait.

You need to keep records of these visits to demonstrate that good practice has been followed. The required frequency of visits will also depend on the nature of the site. An undisturbed indoor site may require fewer visits than one that involves outdoor baiting.

7. Remove bait at the end of the treatment

Any bait left out at the end of a treatment is a continuous source of contamination of wildlife.

So remove all uneaten bait from the site at the end of the treatment and dispose of according to the product label. Again, records of these actions should be kept safely to demonstrate that good practice has been followed.

After the treatment

After the baiting is completed it is time to take action to prevent rats from coming back. The objective is to make the site as unattractive to rats as possible by removing areas where they may harbour and by protecting foodstuffs from their attack.

Killing rats using rodenticides will only provide temporary respite unless further action is taken to make the site less hospitable.

Autumn standby

Lower temperatures and less food and shelter in the fields will drive rodents indoors as autumn sets in and this is the time of year that many farmers step up rodent control programmes.

Stacks of straw and hay are the most likely areas where rats will take up residence, although any dark and undisturbed corner will be attractive.

Once safe harbourage has been found, rats will forage anywhere that attractive food is to be found. Grain silos, flat stores and milling rooms are favoured feeding spots.

Of course, all livestock units are highly attractive to rats because of the perpetual availability of food supplies and shelter. Properly managed rodent control programmes, following the CRRU Code when using rodenticides, are an essential part of modern farming practice.

More information on controlling rodents on farms

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