The complex interactions between predators and their prey are acted out in our gardens on a daily basis. Much of this predation goes unnoticed; for example small insectivorous birds predating aphids, caterpillars and tiny flies. Where predation involves larger animals, such as when a Sparrowhawk kills a Starling, it often catches our attention.
A question of balance
Sparrowhawks, Magpies and other native garden predators have evolved alongside the species upon which they prey. As such, complex interactions work both ways, and the size of the predator population is normally limited and controlled by the prey population. Information from BTO monitoring projects has been used to examine the potential impact of predators on their prey. This research found that, for the majority of prey species examined, there was no evidence that changes in prey populations have been caused by changes in garden predator numbers. The declines seen in many bird populations appear to be due to factors other than predation.
Some predators of garden birds
The Sparrowhawk is a predator of small birds and hunts across many different habitats, including gardens. Sparrowhawks often rely on surprise, using available cover, such as a hedge or a building, to allow them to get close. Females are much bigger than males, so can tackle larger prey (as big as a Woodpigeon) while the males target smaller and more agile prey, such as finches.
Magpies only rarely take adult free-flying birds but will take eggs and nestlings, a behaviour shared by other members of the crow family and even Great Spotted Woodpeckers. Both the native Red Squirrel and the introduced Grey Squirrel are known nest predators. The Grey Squirrel may not be as major a nest predator as was previously thought, seemingly being rather opportunitistic and predating only the more exposed nests. Like Great Spotted Woodpeckers, Grey Squirrels will break into nest boxes.
The domestic cat is an effective ambush predator. There are over ten million domestic cats in the UK, thought to predate as many as 180 million small birds and mammals each year, with the most common prey species being Robins, Blackbirds and Wood Mice.
The cat population is far higher than those of other predators (e.g. approximately 35,000 pairs of Sparrowhawks), and cat numbers are not controlled by prey populations. Cat predation can be a particular problem in urban areas, where cat densities are high, and predation rates are highest in spring and summer.
Predators in the garden... Reducing the impact on feeding birds
By thinking about where you position your feeders you should be able to reduce the risk to birds from predators. Birds need to be able to spot an approaching predator, and also benefit from having cover in which to hide if a predator appears. Low cover can mask the approach of a cat, but not having enough cover will leave birds exposed.
Position feeding stations in the open, with a good distance between them and any low cover such as bushes or flowerbeds.
Raising feeding platforms off the ground and attaching a wire-mesh fence or cage may reduce the risk of attacks on ground-feeding birds.
There are various cat deterrents on the market, including sonic devices that trigger an unpleasant sound when a cat crosses in front of them.’ to read ‘There are various cat deterrents on the market, including sonic devices that trigger an unpleasant sound when a cat crosses in front of them. Devices will need to be move around the garden regularly to ensure the cats don’t learn to avoid one area.
If you own a cat, and it will wear a collar, consider fitting a bell. A study in New Zealand showed that bells reduced rates of predation by 50% for birds and 61% for small mammals. You should also keep your cat in overnight, as this is when most predation occurs.
Position your feeders and bird tables close to high cover, ideally thick evergreen bushes, into which birds can dive at the approach of a Sparrowhawk.
Sparrowhawks rely on surprise, so to reduce the effectiveness of attacks you could move your feeders around the garden on a regular basis. This makes it harder for the Sparrowhawk to predict where it might find its prey.
Consider using a cage which goes around the feeder and restricts access, preventing larger birds from getting in.
Avoid placing feeders next to windows, especially patio doors, as a Sparrowhawk may panic small birds into the glass, either killing them or stunning them.
Predators in the garden... Reducing the impact on nesting birds
Cats and Magpies
Put up nest boxes in inaccessible places; for example, don’t put a nest box near the roof of a shed or a fence where it would be within easy reach of a cat.
Protection for open-nesting birds from cats, Magpies, and other predators can be provided by planting thorny bushes for nesting, which are more difficult for a predator to access (see box). When young birds leave the nest they are unable to fly very well for a few weeks; dense, thorny cover in the garden will provide a hiding place for young fledglings.
Squirrels and woodpeckers
Grey Squirrels gnaw around nest box entrance holes until they are large enough for them to enter. Woodpeckers may hammer at the wood at the level of the nest contents, usually leaving the hole untouched.
Metal plates placed around the entrance hole of a nest box can work, but nest predators may break in elsewhere on the box. Woodcrete boxes, made of a mixture of sawdust, clay and concrete, are effective against squirrels and woodpeckers.
Plants that provide nesting cover
Berberis darwinii (Darwin’s Barberry)
Berberis gagnepainii (Gagnepain’s barberry)
Crataegus monogyna (Common Hawthorn)
Hedera helix (Ivy)
Hippophae rhamnoides (Sea Buckthorn)
Ilex aquifolium (Holly)
Prunus spinosa (Blackthorn)
Pyracantha species (Firethorn)
Rosa canina (Dog Rose)
Rosa rubiginosa (Sweet-brier)
Rubus fruticosus agg (Bramble)