It is probably fair to say that soft fruit like strawberries are not uniquely attractive to birds, but they are certainly high on the list of garden plants that suffer most from bird damage. Birds of many types find soft fruit plants worthy of their attention at most times of the year. The fruit are clearly desirable to them as food in the summer, although they tend to ripen at a time when there is plenty of other food material available. Most gardeners find that it is during the winter months that birds cause the greatest damage by feeding on the buds, and it's in cold months, with food supplies in general fairly low, that a fruit cage really pays for itself.
I know that I share many other gardeners' sentiments in saying that I simply couldn't grow soft fruit without proper protection. At a pinch, canes and bushes can be protected by throwing loose netting over them, but this rarely very satisfactory and I have to say that my own considerable investment in plants and time would be wasted without the added cost of a decent cage. There are now several proprietary fruit cages available in fairly readily assembled kit form. Most comprise a light tubular aluminium frame over which lightweight plastic netting is fitted.
Modern modular construction means that almost any size of cage can be constructed to fit your own range of plants. Alternatively, a more robust cage can be made from rustic poles of treated timber, if preferred.
The netting should be chosen carefully and be of a mesh size that excludes small birds and yet be unlikely to trap their legs. The ideal mesh is between about 0.5in (1.3cm) and 0.75in (2cm) across. The side netting on proprietary fruit cages is usually plastic but galvanised chicken wire makes a stronger construction for cages with wooden frames. Galvanised wire should not be for the top netting, however. Not only is it harder to support than lightweight plastic, but damage to fruit plants will occur from zinc washed from the netting by rain. Lower cages of similar style, about 12in (30cm) tall can be used for strawberry beds, although growing early strawberries under cloches obviates the need for any additional protection.