The type of beak, or bill, a bird has, depends on several factors, most of which can be linked to the type of food they eat.

There are exceptions where the environment has an obviously influencing factor such as the toucan, whose bill is so shaped because they live in extremely hot conditions in the tropics.

Not only are their bills an impressively robust tool designed to crack open the shells of nuts, seeds, some tough fruit skins and even the bodies of lizards and other small birds, it also uses it as a thermoregulator, controlling its body heat through that vast expanse of brightly coloured headwear.

But not all birds in the tropics have that kind of bill, so something else must be at play.

On the whole, understanding the bill shape a bird has can be a very useful way to identify the bird type. If you consider that there are broadly only a handful of different kinds of food out there – seeds, nuts and grains, insects and crustaceans, fruit, nectar, mammals – then you can soon pair up that bird’s diet with the shape of its beak.

Or bill.

You say beakato, I say billato

Right – let’s get that double name issue out of the way. Both beak and bill are interchangeable and there is no right or wrong usage of the word. Although you may find this depends on who you ask, both words refer correctly to the pointy top end of the bird.

Some will say you use the word bill when discussing birds like waders, whose long pokey bills are used to swoop and sift through mud for crustaceans, and beak when talking about birds like raptors who stab, tear and rip their food apart.

But on the whole, either is fine, and our usage throughout the rest of this article is purely based on whichever word feels right in the sentence structure.

Food stuff

Birds like finches that eat seeds and grains have broad, strong and stunted beaks to mash up the hard shells; honeycreepers and humming birds who eat nectar have curved, slender bills for dipping into tubular flower parts; swallows and other birds who feast on insects whilst flying have flattened, wide beaks to snap up their snacks in mid-flight.

‍Eagles, hawks and falcons all have variations on a theme, with sharp and often hooked bills to impale and tear asunder their food.

Dabblers like swans, geese and ducks chow down on vegetation – their beaks are long for reaching below the surface to the water grasses below, and fairly flat to help keep hold of the slimy sustenance.

Sawbills like mergansers are thus shaped to make their pursuit fishing sport as efficient as possible, and to grind their live prey – small fish and aquatic invertebrates and worms, also frogs, and even small mammals – into bite-sized morsels.

Observe the waddling pelican: they love fish, and that huge net-shaped extendable beak shows it. A bird’s bill tells the story of food.

How these hard, bony structures developed over time to be the shape they now are is all down to adaptation, how a species becomes suited to the environmental niche in which it lives.

When things were all a bit up in the air about 60 million years ago, it’s entirely possible there was very little variation among beak shapes at all, until the continents came to rest after the volcanic cataclysm of land mass separating and subsequent continental drift and as all the parts of the planet stabilized into what we know them as today.

But what we also now realize is, the only constant is change.

Feeding frenzy

A recent study on garden birds visiting feeders in the UK found that great tits were displaying a variation in beak shape between two groups in the UK and the Netherlands. Using museum collection records for the UK population spanning 26 years, the researchers found that the bird beaks in the UK were not only longer than their Dutch counterparts', but had dramatically increased in length in recent decades, which happily coincided with the rise in households putting up feeder stations.

UK folk spend twice as much annually on birdseed as do people in mainland Europe. It was theorized that the UK birds’ longer bills had become thus to enable the birds to extract the seeds, normally and naturally found on the ground and in flower heads, from the cages of wire feeders, giving them an advantage over their shorter-billed relatives.

Although the authors of the study declined to flat-out state that bird feeders were responsible, it seemed reasonable to suggest it nonetheless.

Darwinning

Scientists are finding that there are still beak changes taking place every day among many of our bird folk, and by using the research of a modestly famous historical figure to understand what is taking place in our modern times, a whole new field of science is opening up.

The study of epigenetics is the study of how the environment and other factors can change the way that genetic material is expressed, that is, how the environment can bring about changes that are reversible - they do not change the DNA sequence of an organism, but change how the body reads a DNA sequence.

A well-known example of beak adaptation can be seen in Darwin’s finches, a group of around 15 bird species that live in the Galápagos Islands on the equator in the Pacific Ocean.

Due to their geographical isolation, Darwin’s finches are prime research organisms – genetically very similar, but showing extreme variations in certain ways. Research into these songbirds has shown rapid changes in beak size and shape in response to sudden environmental events.

‍Medium ground finches and their relatives, the large ground finches, both experienced a drought in 2004. This led to competition for seeds, then in limited supply.

These seeds were the typical diet of medium ground finches, but because the large ground finches could out-compete their cousins for the seeds, basically by being larger birds, the medium ground finch population underwent an epigenetic shift where their beak size decreased in the subsequent generation.

This dramatic evolutionary change has also been detected in other field studies between the same species of finch. Studies on both rural- and urban-dwelling medium ground finches, living a maximum of 10km apart, found that their beaks were becoming subtly different – more drawn out and less stocky in one, much wider at the base and shorter in the other.

What drives these changes is still being investigated; until now it has always been the go-to theory that food was the influence. But now, there seems to be something else about the environmental factors the birds were experiencing. Research is ongoing…

The science of bird beak morphology is an impressively complex field of study, and one that certainly warrants closer attention; given that there appears to be an increase in dramatic climate and environmental changes afoot in the world today, this will inevitably have an impact on food availability and type.

Keep an eye out on your feathered friends’ dining mechanisms – maybe one day you’ll be identifying that finch because of its flat and long bill, and that raptor’s bill ends in a scoop.

A little far-fetched, we know, but the world is a fascinating place, and we have always looked to birds for signs of change.