Nick Baker’s Hidden Britain
The coal tit’s stashing strategy
I f you are one of the 75,000 Brits who feed the birds in your garden, and you’re blessed with a little curiosity, you might have noticed that your avian visitors don’t just pitch in and eat – they behave strategically. To them, the feeder represents a patch resource: a weird metal tree bearing strange fruit hanging in Perspex tubes and wire cages. To them, it’s an ephemeral source of food, and they act accordingly to exploit it to the maximum. Watch carefully and you may notice a hierarchy, with certain birds displacing others. Close to the bottom of this pecking order will be the coal tit. This small, humbug-headed bird has to be sneaky to outwit the bullying blue and great tits.
Coal tits dash and grab – flying in and quickly out. Follow them and you’ll see that though they might sometimes sit away from the feeding frenzy and delicately dismember a snatched peanut or sunflower heart for immediate consumption, most often they’ll whizz off to some secret corner of the garden and return minutes later to repeat the process – engaging in what scientists call scatter hoarding.
Making continuous repeat visits allows them to dodge the competition. By hiding each prize discreetly in moss, leaf litter, crevices in the bark of a tree, or cracks in a wall or fence post, they can accumulate more food than birds that simply peck away until full.
This strategy is so effective that related species, such as the marsh tit, can cadge up to a morsel a minute – that’s a staggering 50–60,000 food items each autumn. This number might be as much as three times as high in a bumper ‘mast’ year – a situation that we may be replicating with feeders in our own gardens. Coal tits don’t guard these hidden morsels – but then they don’t really need to. Though a competitor may sneakily follow a tit to a stash, or randomly discover one, such a loss is negligible compared with that experienced by a species that puts all its nuts in one basket and creates a larder, risking the lot if its hoard is discovered.
Corvids are also well known for hiding excess food for later consumption. The European jay can hide as many as 5,000 acorns during one autumn.
This strategy creates one obvious challenge for the caching bird: how to re-find its stash. How, up to a year later, does a species with a pea-sized brain perform these mental gymnastics?
Brain food
In fact, the hippocampus (the part of the brain associated with spatial memory) of foodstoring species grows up to 30 per cent bigger over autumn and winter, swollen with newly generated brain tissue and nerves. As the bird reaches peak memory capacity, it is thought that parts of the brain holding old memories are overwritten with new neural material like a computer disk.
Far from ‘bird-brained’, these species are able to recall an incredible number of stash spots. Jays can remember the locations of between 20 and 70 per cent of their caches.
Inevitably, though, birds do forget the locations of some of their stashes; in addition, some birds are eaten by predators, and some hidden seeds are simply not needed, so may germinate. As a result, these birds make a contribution to the spread of hazel, oak and beech woodland.