A s I was reading about the success of the Powerful Owl project (see facing article), I was reminded of a nasty threat to our owls: secondary poisoning from rodent baits. As Editor of this newsletter, I try to ensure articles are positive and practical to avoid environmental doom overload. I weighed up whether to write this article but decided that most, if not all, Land for Wildlife members would want to help owls, so I hope this goes some way to raising awareness of this issue.
Let’s start by looking at the source of the problem, rodenticides. They fall into two broad categories: first-generation and second-generation anticoagulants. First generation rodenticides require the rodent to eat the bait several times before a lethal dose accumulates. Second generation rodenticides act faster and require only one feed for them to be lethal.
The problem with second-generation rodenticides is that they persist in dead and dying animals and when a poisoned mouse or rat is eaten by an owl, the poison can also kill the owl. Owls are not the only non-target animal affected. Rodenticides can also kill pet cats and dogs, birds of prey and other wildlife that scavenge on rodents. Rodenticides also build-up in animals over generations with one generation passing on the poison to their young. For example, 95% of Barn Owls and 100% of Kestrels in the UK now have some levels of rodenticide in their systems.
The USA, Canada and EU have banned the public sale of second-generation rodenticides with licensed pest controllers being the only people still allowed to use them, and first-generation rodenticides can only be purchased by the public in tamper-proof bait stations.
So that is all quite depressing especially given owls are such magnificent creatures and any encounter with one is a privileged wildlife moment. So what can we do?
If you need to control introduced rodents (please don’t trap our native mice and rats), try to use the old-style manual mice and rat traps, or live cage traps or modern electric traps. Mechanical and electrical traps do not pass on any poisons.
Try to make your house and garden less attractive to pest mice and rats. For example, use rodent-proof compost heaps and chicken feeders that only release food needed by your chickens. Collect fallen orchard fruit and don’t leave out pet food overnight. Remove material where mice and rats nest or shelter. Block openings where mice or rats are entering buildings. By restricting the amount of free food and shelter for rodents, their numbers should not boom to pest levels.
If you do need to use a poison, there are now products on the market that do not use anticoagulants. They instead use sodium chloride (salt) and cause rodents to die of dehydration.
Buying rodent poison can be tricky as you will have to look closely for the active ingredient. First-generation anticoagulants have an active ingredient of either warfarin or coumateralyl. Second-generation rodenticides are usually labelled ‘single-dose action’ or ‘one feed’ and contain active ingredients of either brodifacoum, bromadiolone, difethialone or difenacoum. All common household brands like RatSak, The Big Cheese and Talon use either first or second-generation rodenticides or salt – please read the labels.
People have campaigned for many years to change laws relating to rodenticide use in Australia and I take my hat off to them. I am sure that it is only a matter of time before our love and ecological understanding of owls wins.
Article by Deborah Metters
Land for Wildlife Regional Coordinator
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