It's a suburban thing, if you like. For small gardens or small spaces. Say 450 feet square. But the correspondent who has just sent off for it, has been plagued by cats which have ruined at least four birds' nests in her walled garden and, anyway, she doesn't like cats around the place. You may have heard of something similar for keeping mice away. Hospitals have been known to use them. This one is, Catwatch: "The ultimate cat deterrent and it really does work", says the advertisement she sends on.
The advertisers claim it works on the same principle as quality burglar alarms. it senses movement within its area and sends out a high frequency noise (which humans can't hear), which frightens off the cats. But it doesn't affect your dog or birds. They can't hear it. (You don't frighten off burglars that way surely? But never mind.) It's a device in a weatherproof plastic case, and you can stake it where you want it or fix it in place otherwise. You run it on a PP3 battery, though there is also a provision for a mains adaptor.
The advertisement boasts that it assists RSPB wardens in protecting Britain's second rarest bird, the little tern. It's only a small thing. Six inches by three by two. A gardener friend, a very long time ago, used some thing similar to keep mice off a bed containing acorns, which he valued highly, something out of the ordinary. He didn't know whether the device worked, nothing appeared, and when he dug them up, they had rotted in the ground. Not even a good, active, smelly dog will keep your nests safe in a suburban garden. Cats can walk over the greenhouse roof and reach down into the midst of the scaldies with their claws.
And cats you could be sure, know just how high a dog can jump at them as they lie comfortably on the branch of a tree. And it's the same cat on which you take pity and set out a saucer of milk for because it appears to have no home, the same cat which turns into a tigerish killer when it smells a nest.
Make up your mind. And is there an anti magpie device? The Catwatch people are at Concept Research, Forge House, Therfield, Herts. Costs you over £40. PS. It doesn't hurt the cats, just scares them, says the ad.