Great Tits are cavity nesters, breeding in a hole that is usually inside a tree, although occasionally in a wall, rock face, and they will readily take to nest boxes. The number in the clutch is often very large, but seven or eight white spotted red eggs are normal, with bigger clutches being laid by two or even more hens. The bird is a close sitter, hissing when disturbed.
The nestlings are unusual for altricial birds in having plumage coloured with carotenoids similarly to their parents. In most species it is dun-coloured to avoid predation. The nape is yellow and attracts the attention of the parents by its ultraviolet reflectance. This may be to make them easier to find in low light or a signal of fitness to win the parents' attention. This patch turns white after the first moult at an age of two months, and diminishes in size as the bird grows.
The color of the male bird's breasts has been shown to correlate with stronger sperm, and is one way that the male demonstrates reproductive superiority to females. This is due to an increase in carotenoid, which gives the breast its color, as well as enables the sperm to better withstand the onslaught of free radicals.
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