Barn Owls,Rats and Poison – Brenda

Still on poisons, I wonder how many of us are unknowingly also guilty of causing death. Take owls for instance, at some time in their life most will eat rats and mice. Rats and mice eat the baits we put out for them and are in turn taken by owls.
A study in England some years ago found that the number of barn owls with anti-coagulant rodenticides in their livers increased from 5% in 1983-84 to 36% in 1995-96. These figures were based on over 700 barn owl carcasses found dead during these periods. About half the owls were taken from the road and it is assumed were killed by vehicles, it is also thought that it is possible some of them had been weakened by the poison in their system and this had contributed to their becoming road victims. Only 5% of the owls had actually been killed by the rodenticides but it is felt that the mortality is much higher as the poisoned birds become lethargic and creep away and die in places where they are not likely to be found.
Owls ingesting poison is not new but as rats and mice are becoming more and more resistant to the anti-coagulant poisons, they consume much more before dying. As the rats become weaker they are more easily caught by the owls. The major threat now is that in the long term the anti-coagulant poisons will impact more on owls than on rats and mice. As their resistance to poisons increase and threat from the owls decrease, rats would seem to have a very bright future indeed.
Two hundred years ago the barn owl was the most common owl in Britain, now it is amongst the rarest. Farmers once appreciated their good work in controlling mice and rats and to help protect it built special owl holes in their barns so the owls had access to safe breeding and roosting sites; in the second half of the 19th century the tables turned on these beautiful birds and stuffed owls became popular as did shooting and trapping as it was thought that game was being killed by the birds. By the 1930’s concern as to the decline in numbers began and, in a first for a British breeding bird, a census was organised which concluded that there were about 12,000 breeding pairs of barn owls. Survey results announced in January 1999 showed that only about 1000 pairs remained in Britain. If anyone has updates on this it would be appreciated if you could forward the information to me.

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