During the summer it’s interesting to see the difference between adult birds and the recently-hatched youngsters.
We are all familiar with Great Tits, with their bright white cheek patches standing out against a black head, bright yellow belly, and blue and green upperparts with white wing bars. Juveniles, however, have a yellow ‘wash’ over all their plumage; the cheeks are yellow rather than white, the blue of the wings is greenish, and the black cap is duller and browner. They will lose these juvenile feathers at the end of the summer, when they moult mostly into their clean adult colours. After this time you can tell the males and females apart by the width of the black stripe that runs down the centre of the chest; in females this tapers off towards the belly, while in males it broadens to a wide black patch between the legs.
Originally birds of broad-leaf woodland, Great Tits are now entirely at home in urbanised areas, and a large proportion of our estimated 2.5 million pairs are found in our gardens and parks. Their natural diet includes nuts and seeds, and they are among the most frequently-seen visitors to peanut and seed feeders, though this does mean fewer Great Tits are recorded in gardens in years with a good natural crop of Beech seeds.
Great Tits are very likely to take to nest boxes; being bigger than Blue Tits, they prefer cavities that are larger, with wider entrance holes, though they will nest in a very wide range of natural and artificial holes. They generally nest just once a year, producing a single large brood timed to coincide with the May burst of young leaves in broadleaf woodland, and the resulting peak in caterpillar numbers. The parents need to collect 10,000 caterpillars to raise a brood of Great Tits, which they manage by working 18-hour days for two to three weeks! As with nearly all birds, the nestlings are fed on insects by their parents, as they need protein-rich food for their growth. Adults generally won’t use seeds or fats from bird feeders to feed their young, but these food supplies will benefit the parent birds, as they need high-energy foods during this period of hard work! By early June the young birds will emerge, leading to a peak in Great Tit numbers at bird feeders
In recent years an increasing number of Great Tits with large, tumour-like swellings have been reported; this has been shown to be a new strain of avian pox. It seems unlikely that this new disease will affect Great Tit populations overall, but individual birds can be severely affected. The virus that causes the pox can survive on bird feeders, so it’s particularly important to maintain good feeder hygiene if your garden Great Tits show signs of the disease.