Blue tits learned to raid milk bottles and taught each other how
In the 1920s British householders noticed something odd on their doorsteps: blue tits pecking through the foil caps of delivered milk bottles to drink the cream. The trick spread from bird to bird, a textbook case of learned behaviour passing through a population. It faded only when doorstep delivery and full-fat milk did.
The Eurasian blue tit is a small bird in the tit family, about 10.5 to 12 centimetres long and weighing roughly 11 grams. It has a bright blue cap, a dark stripe through the eye framing white cheeks, a greenish back and sulphur-yellow underparts. That yellow depends on diet: the more yellow-green caterpillars a bird eats, the richer the carotene pigment. Males and females look alike to us, but blue tits see ultraviolet light, and under it a male's crown shines brighter blue.
It lives across temperate Europe and parts of western Asia, favouring oak-rich woods but thriving in parks, gardens and town centres, with somewhere between 20 and 44 million pairs in Europe. Linnaeus named it in 1758, though the Swiss naturalist Conrad Gesner had used the same Latin name two centuries earlier. Genetic work in 2005 moved it into its own genus, Cyanistes, from the Greek for dark blue. Acrobatics define it: it hangs upside down from the thinnest twigs and holds big seeds with one foot to hammer them open.
Few birds take to nest boxes so readily, and a single hole may be reused for years, a new pair moving in when the old one dies. The female incubates while the male brings her food. Seven or eight eggs is typical, though a single female in the UK has laid 14, and the whole clutch can weigh one and a half times as much as she does. At the peak of the season a parent may bring food every 90 seconds. Sitting birds hiss and bite at probing fingers, earning the south-western English nickname Billy Biter.
Life is short. British ringing records show just 38 percent of young birds survive their first year, against 53 percent of adults each year, so a breeding bird can expect about three years. The oldest known individual, ringed in the Czech Republic, reached 11 years and 7 months.
Source: Eurasian blue tit
