I realise I'm on contentious ground here but none the less the gardener's case for both these creatures needs to be aired. Only a few months ago there was once again the usual (is it an annual, biennial or perennial) press outcry against household moggies accusing them (on the basis of rather implausible and highly speculative statistics) of massacring so many millions of poor little furry mammals and/or precious garden songbirds per year. Now as much as I detest the habits of cats playing with prey, and worse, of killing some they do not ever eat, I must concede that this is natural in the sense of in their nature and they are indeed guilty. However I must disagree with the purported scale of the feline tribe's alleged depredations, and as a gardener I consider that on the whole, as with the birds, they are beneficial to us.
Firstly I do find such calculated figures for alleged massacres very dubious. I would point out that when a dead mammal or bird is found it is inevitably Tiddles who gets the blame. Regardless of the demise actually being from accident, old age or poison (modern varieties are formulated to cause rodents to go towards light to prevent them dying in dark places and smelling). An obvious fact is that birds must drop and die somewhere when they get old or if hit by a car on the road outside. And fledglings too often foolishly fly into patio windows. Sure I agree cats do kill; but not all of them. The pet or household moggie under a year old maybe keen but is frequently unsuccessful unless remarkably well taught as from recently feral stock. Likewise as any 'owner' knows older cats sleep all day, and night, and cannot be bothered with killing anything not presented on a plate in the usual corner. Unaltered males rarely kill except when hungry as they have other things on their minds almost all the time, and altered males are far more interested in over-eating and being pampered. It is usually only the young to middle aged female cats who are the successful hunters - so if any are to be reconstructed it is they. (a bell is cruel as it is claimed to damage the cat's hearing)
Secondly, and this is where the gardener's interest comes in, what do cats actually kill? We rarely see prey they killed and ate, though a few feathers, a tail or feet lying about is a give-away. I reckon the majority of hunting cats much prefer a rodent meal to a bird (roast chicken excepted); birds are all skin and feathers and die quickly if not actually or pretending to be stunned, the rodents give much more sport which is relish to a mouser. It is only a minority of feline hunters that go for birds as a first choice. Admittedly cats do kill some birds, but more to our point of view they scare the local birds into believing they will kill them! Meanwhile I maintain the hunting cats ruthlessly and methodically track down (young) rats, voles and mice and generally eat them up -while leaving on the kitchen floor for us only the bad flavoured shrew and mole. In support of their case it is acknowledged that hunting cats are most active at dusk -when the birds have gone home but the rodents are starting about.
As a gardener I suffer damage from both two and four legged vermin. (Indeed the two legged sorts without feathers have proved the worst of and it's a shame they are always in close season!) Birds can be a problem but are easier to keep away than rodents, in particular birds are daytime pests so are more easily disturbed by our activities, and also by scary devices. Rodents do by far the worst damage; they eat seeds, seedlings, the bark off stems, they devour bulbs and corms, and destroy roots and fruits both in the garden AND in our stores. (Some rodents, I believe voles, even ate the flower heads of my fritillaries and stripped the seeds off my strawberries leaving the ruined fruits in neat piles.) Moreover what rodents do not nibble they often urinate on. And they eat other things such as books and electrical insulation! And worst of all rats and squirrels will eat eggs and kill fledglings. It's very hard to deal with rodents, they get in and under netting and chew through many other barriers. I loathe using poison and traps seem no better and are too onerous for a heavy infestation. Rodents are a real pest in the garden and thank goodness cats do control them for us.
Meanwhile the damage to our gardens from birds -seedbeds disturbed, seeds eaten, seedlings razored off, fruit stolen and pecked is more than balanced by their incredible pest control, their additions to fertility and their delightful presence. I don't think we realise just how much good birds do for the gardener, but just one family of blue tits eats tens of thousands of caterpillars in a year. Their droppings may not seem much but in a year add up to a load of high grade guano distributed for free. In addition birds can be much more easily prevented from doing damage with simple barriers of wire and netting, glitterbangs and similar. And some barriers can simultaneously keep cats from fouling the soil and damaging the crops. (Apparently the easiest way to keep your beds from being fouled is to make the kids a sandpit! So make one just for the cats in a discreet place and regularly change the fouled sand which is probably then best buried by the roots of trees and shrubs.)
You cannot train the rodents or hardly the birds but cats are subject to coercion and bribery. I have found that if you consistently show anger and disdain when they kill birds and give congratulations and treats when they kill rodents and moles then they soon learn. (Admittedly I'll concede they may just learn to be sneaky but I haven't caught them out.) They can also be trained to catch moles if that is your want by the simple expedient of putting cat biscuits in mole holes and showing the cats... The cats (of which I currently have four) now rarely ever take a bird, but the birds do not realise this. So my lazy crew contentedly dozing around the garden dramatically reduces the bird damage IN WARM WEATHER!
In cold weather they are inevitably in the greenhouse, the stores or indoors by the Rayburn, thus all late autumn, winter and spring the birds are relatively free to search for seeds and insects throughout the whole garden. It is only when the weather warms up that the cats are abroad. In these warmer months the birds are likely to find food elsewhere so the presence of cats easily encourages them to go there leaving your own seedlings and fruit unmolested. A few live cats can also be augmented with fake cats made from artificial fur, or even teddy bears, as long as these are moved twice a day.
But there is another point always overlooked. Although we must be sad at the loss of any garden bird (I might make exception to pigeons) it is part of life that they all must die sometime. And more importantly they should be granted a relatively quick clean death not a lingering one. In nature the function of any predator is to soon eliminate the old, the sick and the stupid thus keeping the prey population healthy and fully viable. With our urbanisation and destruction of habitat we have eliminated most natural predators that once controlled the rodents and kept bird populations healthy. We have few ferrets, weasels, stoats, kites, kestrels or owls in our housing estates. It's a bloody good job we do keep cats or we'd be overrun with rats, mice and sick birds before the council pest control offices could ever do anything.