Blue Tit

The Blue Tit is such a familiar and widely distributed species that it is all too easily dismissed by some as being of little interest. This, of course, is a rather narrow view of what is actually a rather interesting little bird.

Blue Tit breeding abundance 2008-11
(Click to enlarge)

Blue Tits are very frequent visitors to garden feeding stations, where they are often inquisitive and sometimes confiding. They are, however, primarily birds of lowland deciduous woodland, something reflected in the recently published abundance maps produced for Bird Atlas 2007-11. These maps show measures of Blue Tit abundance to be lowest in the uplands and across the open, treeless, landscapes of the Fens, while relative abundance measures reach a peak in the woodlands of south-east England, particularly from the north of London south across the Weald to the south coast.

Boxing clever

The Blue Tit is a common tenant of garden nest boxes, typically favouring those with a small entrance hole (c.25mm diameter). The size of the entrance hole is important because smaller, less dominant species, like Blue Tit, may be ousted from otherwise suitable cavities by larger species like Great Tit or House Sparrow. Nest box design and placement have also been found to influence occupancy in tit species, a pattern additionally shaped by the competition between species

Blue Tits are single-brooded, opting for an ‘all your eggs in one basket’ approach, that sees clutch sizes typically in the range of 8-10 eggs, (although clutches of 16 have been noted by BTO Nest Recorders). In years or sites where there is plenty of food they will do very well, but in poor years they may well lose the whole brood.

Individuals may be seen investigating potential cavities, including nest boxes, very early in the year. Such visits may be just a reflection of the tit’s inquisitive nature or they could be individuals checking out potential overnight roosts. The increasing use of nest box cameras by garden birdwatchers has highlighted the degree to which nest boxes are used on winter nights by blue tits and other small birds for roosting. Presumably the boxes provide shelter from the worst of the winter weather and reduce the quantity of body reserves spent overnight in keeping warm. If you have a camera, then turn it on one winter evening to see if it is being used for roosting.

Parental investment

An average clutch of Blue Tit eggs contains roughly 0.5 g of calcium, which might not sound like a lot; but given that there is only about 0.6 g of calcium in a Blue Tit skeleton, this represents a significant investment for the female and it is likely that she will need to source this from the environment, presumably in the form of fragments of snail shell and other calcium-rich material. As well as the demands around the production of eggs, Blue Tits then have to work hard to provision any resulting chicks. Within a good piece of mature oak woodland, breeding Blue Tits will have access to sizable caterpillar populations but within urbanised landscapes finding suitable food for their chicks can be more difficult and levels of productivity are likely to be lower.

On the move

While our Blue Tits are largely sedentary in habits, individuals from some Scandinavian populations may undertake substantial seasonal movements, very occasionally resulting in the arrival of some of these birds on our shores. Such ‘eruptions’ are rare today – perhaps a consequence of a changing climate or because of increased provision of food at garden feeding stations by Scandinavian householders. Local movements of British and Irish Blue Tits are equally fascinating, with the birds ranging over an area and moving around in small flocks that often include other tit species, Goldcrest and wintering Chiffchaff. You may think that you only have five of six different Blue Tits using your garden feeding station in the winter, but you could easily have ten times this number passing through during the course of a single day.

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