Rodenticides and the risks of Brodifacoum for owls
|Article submitted by
Jan van 't Hoff, on behalf of
Wies and Peter Beersma. 2002-10-01|
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
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
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: email@example.com) 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
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: firstname.lastname@example.org) describes a programme to monitor the
levels of rodenticides in Barn Owls in Britain, and assess the effects 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.
- Fortunately there are some animal
and environmental alternatives for these rodenticides to hand. Combat
rodents for example:
- In a mechanical way by means of
mousetraps or with an electronic instrument to chase rodents away;
- In a biological way, simply with
the help of your cats;
- 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;
- By constructing an easy, but owl
friendly micebox (for a drawing and description see
- And if one buys rodenticides,
always avoid the use of Brodifacoum.
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