Watching the birds on my bird table, I am always impressed by the dexterity of their manoeuvres in dealing with food. Their bills might seem crude in comparison with human fingers, but with the aid of their tongues and sometimes a little juggling they can handle a variety of seeds and other foods. Some, like the greenfinch, actually seem to prefer to work at their food, teasing open sunflower husks to get at the seed within.
Beaks (or bills, the terms are interchangeable) are a bird’s most important tool, used in finding and capturing food, preening, courtship, defense, nest building, communicating, and feeding young. They have evolved to allow them to adapt to different environments. Ask an avocet what to do with a dead rabbit and you won’t get an answer; likewise if you need to get at those juicy lugworms on the sea shore don’t ask an eagle.
Beaks are a primary indicator of polymorphism, in which two or more forms appear within the same species. Darwin famously considered variations in beak size and shape in species of finch in the Galapagos Islands in his development of the theory of evolution. Sometimes beak size and shape go along with other characteristics, such as song. The large cactus finch, for example, has two distinct types, ‘A’ and ‘B’. ‘A’s have shorter beaks and can tear apart the base of the prickly pear to get at the flesh and any insect larvae; whereas ‘B’s have longer beaks with which they pierce the fruit to get at the pulp that surrounds the seeds. Slight variations in beak morphology can give an individual bird an edge in the pecking order.
A beak, more than any other part of a bird, indicates its particular niche in the evolutionary jigsaw. It is, figuratively speaking, the ‘point’ of a bird: what it does, what it is. Ted Hughes knew this when he wrote about “the bounce and stab” of a thrush’s hunting movement as it searches a lawn for food:
Terrifying are the attent sleek thrushes on the lawn,
More coiled steel than living – a poised
Dark deadly eye, those delicate legs
Triggered to stirrings beyond sense – with a start, a bounce,
Overtake the instant and drag out some writhing thing.
No indolent procrastinations and no yawning states,
No sighs or head-scratchings. Nothing but bounce and stab
And a ravening second…
(Thrushes by Ted Hughes)
Crossbills have one of the more unusual beak formations. These little finches are incredibly adaptable, and can breed in the winter months in order to get the best crack at the crop. The beaks of different populations have evolved in ever so slightly different forms to cope with different food sources. They all specialise in feeding on various forms of conifer seeds, and their weird beaks act like pocket knives to get at the foods other birds cannot reach. When courting they grab each other by the bill, in a gesture known as billing.
Hawfinches have the largest bill of any British finch. Theirs is a mighty weapon indeed, which can crack a cherry stone using a pressure equivalent to more than 60 tonnes! These formidable little birds can rip chunks of flesh out of the hands of the unwary handler; yet they too have a tender side to their nature: in courtship they will tap each other’s beaks in a gesture not unlike a kiss.