RSPB -
The apparent disappearance of birds in August is another natural change and a part of the annual cycle of birds. There are two reasons for this.
Firstly, once birds have completed their breeding for the year, they start to moult into fresh new feathers. Completing a moult of all feathers takes several weeks. During this period birds look rather scruffy, and while they are moulting their wing feathers, they are less able to escape predators.
During this time, they conceal themselves as much as possible to avoid predators and territory disputes. It's easy to get the impression that they've disappeared.
Secondly, in late summer a bounty of natural food becomes available as grain, berries and fruit ripen. Many birds abandon their nesting areas and move to where the most food is. This is probably the time of the year when birds are least interested in the offerings on our bird tables.
In areas where farmland is nearby, house sparrows, starlings and many finches move out to fields to feast on the abundance of grain before it is harvested, and on the spilt grain after the harvest. Depending on the location, this can cause a sudden disappearance of these birds from residential areas and gardens.
Even in cities, sparrows and finches are attracted to any piece of rough ground that provides a good crop of weed seeds. Tits tend to abandon their territories soon after their young fledge, and spend most of their time in the late summer (first in family groups, later in larger flocks) high up in tree canopies, where they are easily missed. Even blackbirds and song thrushes tend to move to where there is an abundance of fruit or berries.
Birds often only return to our gardens when autumn frosts appear.
I feel reassured now