Wildlife Poisonings

by Maree McCarthy, Nature's Magic Garden Designs

I was working on a garden in Cardiff (NSW) last week when suddenly a Tawny Frogmouth fell out of the tree next to us screaming and throwing its head back and rolling its eyes in pain.

It screamed very loudly for the whole 20 minutes or so it took for us to pick it up and take it to the nearby vet. The vet said she'd call the native experts - wildlife carers. She said it looked thin but had no broken bones or obvious injury. It was most likely poisoned by rodent or cockroach bait poison.

Then I read in the February Landcare newsletter that there are people also upset because they found other animals poisoned recently - at Green Point Foreshore Reserve they found 'a Masked Owl, Kookaburras and Ravens', and at Valentine, 'a 1.5metre Diamond Python' - all apparently poisoned by mouse and rat baits.

How the Poison Works

Rodenticides are dangerous. When wildlife see a mouse, rat, or cockroach running around, they eat it - unbeknown to them that it has been eating a poison and probably the reason it was easy to catch.

All rat poisons are dangerous but some are worse than others. Most are based on anticoagulants and are of 2 basic types - multi-feed (eg. the chemical warfarin (Ratsak), and coumatetralyl (Racumin); and single-feed rodenticides (eg. brodifacoum (Talon), bromadialone (Bromakil).

Brodifacoum (single feed) is about 40 times more potent than warfarin and can easily kill an owl that eats the mouse or rat - and even fish if it gets into a stream or pond. It is also a highly cumulative poison.

Signs of poisoning include: anaemia from blood loss over several days; bloodstained faeces, blood appearing in the saliva or appearing from the nose, breathlessness from blood pooling in the chest cavity; weakness; crying out in pain, and convulsions.

Alternatives

Information offered at en.wikipedia.org/wiki/Rat_poison includes:

Traps such as the old wooden traps, cages, and drums where they fall in with a 'see-saw' added.

An alternative is the use of biological, non-toxic, yet lethal baits, consisting of anhydrous powdered maize/corn cobs, containing high fractions (over 40%) of a-cellulose, which is incorporated into a solid, gastric-resistant matrix, that is dissolved in the gut. The a-cellulose anhydrous powder released in the gut of the rodent disrupts water and electrolyte balance and so kills the rodent. This material is commonly formulated with taste and flavour additives to increase its palatability, and is compressed into granulate of appropriate size (granules of bigger size for rats, smaller granules for mice).

This material is completely non-toxic, leaves no harmful residues, is environmentally friendly and accidental ingestion of it by pets or children is simply treated by giving laxatives, plenty of water and electrolytes. Dead rodents killed by this mean pose no risk of secondary poisoning.

Newer rodenticides have been developed to work by reducing the sperm count in males, thus depriving them of the ability to procreate, rather than to kill the rodents outright. These are usually administered in the breeding seasons of most rodents.

Of course, the best idea is to eliminate the problem in the first place by making sure rats and mice can't get to where you don't want them, by keeping all food scraps in tight containers they can't get to, and by making sure your compost bins are buried very deeply so they can't tunnel under.

Landcare will issue fact sheets soon.

Image sources:

Tawny Frogmouth image courtesy of Royal Botanic Gardens Sydney, by P. Garlick (copyright).
Kookaburra image by Mary Trigger, copyright SGA.

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