[Tweeters] rat poison and birds (wildlife)

Kevin Purcell kevinpurcell at pobox.com
Thu Feb 4 18:08:42 PST 2010

Apologies for the LONG stream of consciousness post.

And those who don't like citations and web links better stop reading
now. :-)

On Feb 4, 2010, at 1:35 PM, Barbara Deihl wrote:

> I received this message yesterday from a concerned pet owner and

> bird-watcher with whom I have corresponded regarding her interest in

> and sightings of a Cooper's Hawk and a Merlin in her neighborhood.

> I put her onto a couple of sites online about Contrac (they included

> an MSDS sheet), but I think some personal experiences dealing with

> this issue would have extra impact. Many of us deal with this

> conflict and could use some advice. The inquirer was also concerned

> with the possibility of birds ingesting the grainlike poison

> directly from the ground.

The active ingredient is Bromadiolone. It's a variation of coumarin
(to which quite a few rats are resistant).

This site has a copy of the WHO/FAO Pesticide datasheet.


> Bromadiolone is an anticoagulant, highly toxic to rodents and highly

> toxic to other mammals.

i.e. it prevents blood clotting. I doubt it would affect the eggs
(that was a specific effect of DDT/DDE) but it might directly kill a
bird or its offspring.

LD50 (lethal does 50%) is the dose required to kill half of the test

> 2.1.4 Toxicity, single dose:

> Oral LD50


> Rat 1.125 mg/kg b.w.


> Mouse 1.75 mg/kg b.w.


> Rabbit 1 mg/kg b.w.


> Dog > 10 mg/kg b.w. (MTD)


> Cat > 25 mg/kg b.w. (MTD)


> 2.3.2 Birds:

> Oral LD50


> Quail


> 1600 mg/kg b.w.


> Poultry are sensitive to bromadiolone. A bolus oral dose of 1.25 mg/

> Leghorn hen/day, for 10 days, killed 2/10 hens. A dose of 2.5 mg/hen/

> day for 30 days killed eight of the 10 hens tested.


> 2.3.3 Other species:

> No published information available.


So not direct info we want. But it does permit some back of the
envelope calculations.

Leghorns typically weight 2kg to 3kg so one might estimate a LD50
total dose is between 4mg/kg and 25mg/kg to but this kill rate is
slower than the five days for rats (from a single dose).

But for "quail" the LD50 is 1600 mg/kg. The paper below gives the LD50
for Bobwhite Quail as 138mg/kg.

So there is a about 100 fold range of sensitivity in birds.

A typical rat weights 0.25kg to 0.5kg so perhaps he'd be loaded with
maybe a few mg.

This paper "The status of bromadiolone in the United States" RM Poche
- Proc. Vertebr. Pest Conf, 1986 - is available from

(a PDF)

The source is a maker of the product but they show the drug is mostly
metabolized and excreted by the rat before it dies after several days
(see the Nontarget Hazard Potential for which there are lots of
qualifiers). They also quote a UK study on Barn Owls where 1 of 6 owls
fed with bromodialone died (though it had the highest mass and the
lowest overall does but ate the most livers where bromodialone
accumulates). As they point out that was 10 days feeding only in rats
that had been given a lethal dose.

A closely related compound brodifacoum that has a much longer half-
life in the rat (and birds) and perhaps should be avoided (sometimes
it's used with bromodialone) see the American Bird Conservancy link.
The ABC does not mention bromodialone on their site though they ones
they do mention are all pretty nasty.


This paper may have some of the info we want


but only the first page is free (those with a University subscription
might want to chip in ...) and they don't have a abstract summarizing
their results (I hate that).

Finally there is a paper (in JSTOR ... not free but if you are at a
univeristy site yo have access).

Rodenticide ecotoxicology: assessing non-target population effects
PR Cox, RH Smith - Functional Ecology, 1990 - jstor.org


> Rodenticide ecotoxicology: Assessing non-target population effects.

> Cox, PR | Smith, RH

> Functional Ecology [FUNCT. ECOL.]. Vol. 4, no. 3, pp. 315-320. 1990.


> Environmental hazards presented by pesticides and other toxicants

> are determined by exposure as well as toxicity. Predicting and

> estimating exposure is much more difficult than measuring toxicity

> since exposure depends on toxicant distribution, individual

> behaviour and population dynamics. We present a generalized

> compartment model for ecotoxicology and illustrate its use in

> relation to rodenticide hazard evaluation. The model highlights the

> need for particular sorts of field experiment. We present the

> results of a series of field experiments designed to assess

> potential effects of rodenticide use on some non-target animal

> populations.

The first page is free and warns that simple lab numbers like those
quoted above may not actually work out in the field.

Anyone who can help with these papers should contribute.

by WB Stone - 1999 - Cited by 37 - Related articles

> ABSTRACT: From 1971 through 1997, we documented 51 cases (55

> individual animals) of poisoning of non-target wildlife in New York

> (plus two cases in adjoining states) (USA) with anti-coagulant

> rodenticides—all but two of these cases occurred in the last 8 yrs.

> Brodifacoum was implicated in 80% of the incidents. Diphacinone was

> identified in four cases, bromadiolone in three cases (once in

> combination with brodifacoum), and chlorophacinone and coumatetralyl

> were detected once each in the company of brodifacoum. Warfarin

> accounted for the three cases

> documented prior to 1989, and one case involving a bald eagle

> (Haliaeetus leucocephalus) in 1995. Secondary intoxication of

> raptors, principally great horned owls (Bubo virginianus) and red-

> tailed hawks (Buteo jamaicensis), comprised one-half of the cases.

> Gray squirrels (Sciurus carolinensis), raccoons (Procyon lotor) and

> white-tailed deer (Odocoileus virginianus) were the most frequently

> poisoned mammals. All of the deer originated from a rather unique

> situation on a barrier island off southern Long Island (New York).

> Restrictions on the use of brodifacoum appear warranted.


Note in this case of the 51 cases only 2 involved bromadiolone alone:
4% of the cases (one every other year in three states).

And another UK study

Mortality Causes in British Barn Owls (Tyto alba), Based on 1,101
Carcasses Examined During 1963-1996

> Abstract.—During 1963-1996, 1,101 Barn Owl (Tyto alba) carcasses

> were received for autopsy and chemical analysis. Much larger

> numbers were received per month outside the breeding season than

> within it. A peak in the monthly mortality of first year birds

> occurred in autumn (November) and a peak in the mortality of adults

> in late

> winter (March).


> The main causes of recorded deaths were collisions (mostly with road

> traffic) and starvation. No great seasonal variation occurred in

> the main causes of recorded deaths. Among accident victims, the

> mean weight of females (305 g) was about 5 percent greater than that

> of males (291 g). Most starved birds of both sexes weighed less

> than 240 g.


> Organochlorine pesticide victims formed 20 percent of all dead Barn

> Owls obtained during 1963-1970, and a decreasing proportion

> thereafter. None was recorded after 1976 when the use of aldrin/

> dieldrin was greatly curtailed. During the 1980s and 1990s,

> increasing proportions of birds contained residues of second

> generation rodenticides, but relatively few at sufficient level to

> have caused their death.


Here they find 1% of the owls (i.e. 8) were killed with rodenticide
(but that includes warfarin, brodifacoum, etc) two of them only had
bromadiolone in their liver (and no other rodenticides). So that's

Pesticide Acute Toxicity Reference Values for Birds
by P Mineau


Bromdialone of the rodenticides seems to have the lowest toxicity of
the redenticides (excluding warfarin) see page 66.

Finally there are bromadiolone-resistant rodents out there. Isn't
evolution wonderful. Using it will create more.

It seems the risk is relatively low but non-zero. I agree with Bill
Anderson that there are other methods (e.g. trapping) that remove this
Kevin Purcell
kevinpurcell at pobox.com
twitter: @kevinpurcell

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