The private lives of tits

A REALITY show with a difference is running on the internet.

It features a blue tit nest in Derek Mooney’s garden at Kilmacud in Dublin. The nest-box has a television camera inside it with another one focused on the tits’ front door, the tiny hole through which the pair enter and leave.

With almost three million blue tits in Ireland, such nests are commonplace. Yet the interest in this little family has been phenomenal. The number of hits to the website on Friday, May 11, the day the eggs began to hatch, was 24,276 and the total since ‘live screening’ began is over a 250,000. Paddy Power Bookmakers is giving odds on the fledging date of the babies.

Blue tits love to nest in boxes, and this makes them easy to observe; it’s not surprising they are among the world’s most extensively studied birds. In Britain and Europe, blue tits compete for resources with four other tit species; in Ireland, they have only two rivals. Our ones, therefore, occupy a wider ecological ‘niche’ than their foreign cousins.

Apart from their interest to science, blue tits are the most entertaining of our little birds. Marvellous acrobats, they are resourceful and intelligent. In 1929, a blue tit broke open a milk-bottle top in Southampton to get at the cream. Others copied the little burglar and the craze spread. Soon, milk raids had become a nuisance throughout these islands. Then there are two well-documented cases of tool-use by blue tits; one prized peanuts from a feeder with a twig, another used a pine needle as a table fork. Tough little fighters though, blue tits bite when being handled and ringing them is no fun.

A pair nested successfully in Derek’s box last year. About 70% of adults die annually and the divorce rate is around 25%. Between deaths and divorces, therefore, the odds that last year’s pair have returned are fairly slim. The female is more likely to be back than the male. Although males rule the roost during most of the year, the female is boss in the breeding season, and she chooses the nest site. Last year’s female, if she survived, would probably return to the box with either her old partner or a new one in tow.

Nest building began in April. Male tits bring some material but the female does most of the work. She ‘decorates’ the nest with leaves of ferns and nettles, the odours from which probably discourage insect parasites. This year’s nest is particularly bulky and untidy, making it difficult for the camera to see deeply into the cup.

The first egg, we think, was laid on April 20, followed by seven more, one each day. The adult weighs about 11 grams. A full clutch is as heavy as the mother and she must consume huge amounts of food while she is laying. The male helps by bringing her juicy treats. It used to be thought that this ‘courtship feeding’ was a ritual, or a prelude to mating, but we now know the food donated by the male is a vital source of extra nourishment. He contributes about 40% of her food needs during the early breeding season. Still, she has to feed so often during the laying period that there is no time to incubate; as the newly-laid eggs cool, cell division within them ceases temporarily.

Incubation began on April 27. Only the female sits. She does so almost continuously, taking occasional short breaks to feed and stretch her wings. The male keeps bringing the takeaways. Nests in boxes, particularly when lined with hair and feathers, are well insulated and embryos develop quickly in the warmth.

Blind and naked babies can just detect the shadow of a parent above them and open their bills for food. Snug in the nest, they sleep most of the time and little energy is wasted — a most efficient system. Small chicks can’t control their body temperature; the mother must ensure they don’t chill and she spends much of her time in the nest. Food demands are modest when the chicks are small but, like children, their appetites improve as they grow and the pressure on the parents mounts relentlessly. Demand peaks around the ninth day after hatching. By then, the parents will be making about 1,000 deliveries per day. Each chick receives between 90 and 100 caterpillars, spiders or bees between dawn and dusk.

Trees hate caterpillars, which gobble up their leaves, and tits are allies in the war against these pests. Chemicals are the weapon of choice; trees produce tannins to poison the caterpillars but these can be a problem for the tits.

As the season progresses the amount of poison in the bodies of the caterpillars increases, making them toxic to nestlings. Captive chicks, fed experimentally on mealworms laced with tannins, grew much more slowly than normal ones.

The blue tit’s larger cousin, the great tit, pulls the heads off caterpillars and removes their digestive organs, where the toxins are concentrated, before feeding the babies. We don’t know if blue tits do this; they are difficult to observe high in the canopy.

See www.rte.ie/mooney