Rodenticides and the risks of Brodifacoum for owls

Many farmers and people who live out in the country don't realize the risks of using rodenticides against mice or rats. Nowadays we are faced with second generation anticoagulant rodenticides, which are very toxic for rodents, and for small mammals and birds as well.
Rodents are the main prey for owls, many birds of prey and martens. In an indirect way these predators become poisoned too, and in some cases even killed. Among these birds there are characteristic farmland birds like the Barn Owl and Little Owl. Owls that are often living in or nearby farms. There's much evidence that Barn Owls are killed by Brodifacoum, and evidence about the Little Owl that there is serious reason for concern.

Brodifacoum is found in a lot of products as listed below:
In Europe, Brodifacoum has been worked up into the following products which are freely available on the market: Broditop (Italy), Finale, Folgorat, Havoc, Klerat, Mutikus, Mouser, Ratuk +, Rodend, Talon, Volak and Volid (source: www.inchem.org; detection limit for Brodifacoum 2ug /kg).
It's unknown in which countries these products are obtainable or not. In the Netherlands for example, from the listed products, only Klerat is available.

Beside Brodifacoum there are 4 other rodenticides on the market: Difenacoum, Bromadiolon, Difethialon and Chloorfacinon. Of these rodenticides only Bromadiolon has been allowed for outdoor use. Difenacoum, Brodifacoum, Difethialon and Chloorfacinon are meant for indoor use.

From the Netherlands it's known that these elements are the effective substance in the these products:
Difethialon in FRAP, TARGET
Bromadiolon in Super CAID, SPRIGONE, BROMATROL and TOMCAT (HOME) BLOX
Brodifacoum in KLERAT
Difenacoum in SORKIL-G, CASTRIX special, DIFENARD, FENTROl, RADICAAL, RATAK, RATTOX-G, RODEX, SOMITROL-N
Chloorfacinon in FINITO.
Unfortunately, we lack this kind of information from other countries.

According to the following sources Brodifacoum has a significant higher level of poisoning to owls, especially to Barn Owls and probably to Little Owls as well:

In Wildlife Society Bulletin 8 (4) 1980: 311-315 Mendenhall & Pank already report on tests with Barn Owls (Tyto alba) and anticoagulant rodenticides. In groups of 6 Barn Owls, 1 owl was feed 1 day with Difenacoum, Bromadiolon and Brodifacoum, 2 owls 3 days, 1 owl 6 days and 2 owls 10 days. Barn Owls consuming poisoned rodents for only 1 day didn't show any perceptible sensitiveness in a 3 weeks observation period. Rodents poisoned with Difenacoum and Bromadiolon in 3 successive days caused no harm at the owls, but with Brodifacoum the birds died. After 6 and 10 days foraging the Difenacoum group showed bleedings, but no mortality. With Bromadiolon 1 of the 2 owls, which had foraged on poisoned rodents for 10 days, died. With Brodifacoum both Barn Owls died.

In Planter 60 (1) 1984: 3-11 (Kuala Lumpur) Duckett informed about the mortality, in a period of 2 years, from 38 of the 40 present Barn Owls on a Malaysian plantation after a substitution of the resistant biocide Warfarin by Brodifacoum.

In Environmental Pollution 103 (1) 1998: 17-23 McDonald, Harris, Turnbull, Brown & Fletcher proved the existence of remnants of Bromadiolon and Brodifacoum, and the combination of both biocides, in the livers of Stoats and Weasels.

In Journal of Wildlife Diseases 35 (2) 1999: 187-193 Stone, Okoniewski & Stedelin described 51 well documented cases of mortality by anticoagulant rodenticides in non-target species, mammals as well as birds. 80% was caused by Brodifacoum. Poisoning by other biocides were partly in combination with Brodifacoum.

According to Bowles in Environmental News Network of January 1999 the number of Barn Owls in England with anticoagulant rodenticides has increased from 5% in 1983-84 to 36% in 1995-96. He also described the poisoning of a Red Kite fledgling after foraging on a rodent infected with Bromadialon.

About the negative effects of anticoagulant rodenticides on the Little Owl (Athene noctua) is little known yet, but we assume a comparable vulnerability for Brodifacoum as in Barn Owls.
In the Netherlands in the past 25 years, 13 Little Owls had been examined only about insecticides, of which one was found positive (Parathion).
Recently Peter Beersma (e-mail: ath-noctua@planet.nl) has started research into the damage caused by rodenticides on Little Owls. For more information see the article in Oriolus 67 (2-3) 2001: 94-99 by Peter and Wies Beersma or download the pdf-file "Rodenticides" on www.steenuilgroningen.nl, Or have a look on www.steenuilgroningen.nl/dode-steenuilen (a Dutch site with a special page about death Little Owls; also in English).

In his paper "Rodenticide effects on British Barn Owls" (a contribution to The Owls 2000 conference in January 2000, Canberra, Australia) professor Ian Newton (e-mail: i.newton@ite.ac.uk) describes a programme to monitor the levels of rodenticides in Barn Owls in Britain, and assess the effects on populations. On www.tasweb.com.au/owls2000 he further writes: "the fact that rats and mice in many parts of the world have become genetically resistant to Warfarin and other 'first generation' rodenticides has stimulated chemical companies to develop new 'second generation' compounds for use in rodent control. The new compounds are more toxic and more persistent than the old ones, with the potential to cause secondary poisoning in rodent predators".

More information about Brodifacoum (in Dutch) you'll find in Zoun 1999.
BRODIFACOUM Samenvatting van de toepassingen en de physische, chemische en toxicologische eigenschappen. Afdeling Immunologie, Pathobiologie en Epidemiologie ID-DLO Rapport no. H 99-687, Lelystad, the Netherlands.

Alternatives:

1. Fortunately there are some animal and environmental alternatives for these rodenticides to hand. Combat rodents for example:
2. In a mechanical way by means of mousetraps or with an electronic instrument to chase rodents away;
3. In a biological way, simply with the help of your cats;
4. By producing a wet flourball that consist of 1 part of sugar, 2 parts of lime and 3 parts of flour. In rodents that eat from these flourballs it causes a constipation in the intestines, by which the animals will die within 2 days;
5. By constructing an easy, but owl friendly micebox (for a drawing and description see www.steenuilgroningen.nl).
6. And if one buys rodenticides, always avoid the use of Brodifacoum.

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