Of birds and their beak, And what they eat D. Indumathi, The Institute of Mathematical Sciences, Chennai Early morning is a good time to watch birds getting busy about their daily tasks. One of the most important ones is getting food. In fact, this is an important aspect for most living things, including ourselves. But our food comes to our plate, while birds and animals have to forage for it. Birds have developed different kinds of adaptation to their local environment. In particular birds do not have teeth. (That is itself an interesting story; see the accompanying article in JM). So their beaks are specially modified to be able to eat the food that they prefer. In fact, birds have one of the most varied diets, including fruits, plants, seeds, and even nectar, as well as other smaller animals (and fish). So the digestive system of birds is very special. It has three unique parts: a beak, a crop and a gizzard apart from the usual components. See box for details. BOX: Bird's digestive system You must have often seen birds quickly picking up food or worms and pecking away at great speed. Apart from the beak and mouth where food enters, and the throat (pharynx and eosophagus) that we also have, birds have a special “crop” to store food. When a bird finds food, it has to eat it as soon as possible (before a rival comes and eats it up). The bird swallows the food and stores it in the crop, and this is later slowly digested in a safe place, far from predators. Wish we could do this too: swallow breakfast quickly and slowly digest it in class! The stomach has two parts, the proventriculus and the gizzard. The first part is especially useful for birds that swallow fish whole and need to digest it whole, including the bones. The gizzard has very strong muscles which are used to grind the food. Birds pick up and swallow sand and small stones and store them in the gizzard. The food is mixed with this in the gizzard and crushed by the muscles. So the stones help grind the food. In fact, the gizzard is very specialised and different depending on the kind of food the bird eats. END OF BOX What birds eat So, what do birds eat? Birds that eat different kinds of food (fruit and insects) are called generalists, while others that prefer specific food items or have a special strategy to obtain food are considered specialists. Generalists forage across open and forested habitats. So they promote growth of tropical forests and increase plant diversity. Which birds eat grains? Granivorous birds eat seeds and grain. This is the primary diet for many types of birds, especially sparrows, and finches. Many of you may have put out rice, corn or seeds for the local birds in your garden. Pigeons and doves are especially common in urban areas. Parakeets are commonly sold as pets although this is illegal in India. Some grain eating birds are treated as pests by farmers because they can destroy crops. Smaller birds with small, sharp bills will choose smaller seeds such as millet. Larger birds prefer larger seeds such as sunflower seeds. Some seed-eating birds have very specialized bills, such as finches and some woodpeckers, with big beaks and tongues, which can crack pine cones open to get the seed. Nectar feeders Nectar is a sweet, nutritious liquid produced by some flowers. It has two jobs: one to feed insects and birds which eat the nectar. At the same time, these help to pollinate the flower and so help it to reproduce. Nectar feeders such as sunbirds and hummingbirds have specially adapted brushy tongues and long bills designed to probe for nectar and directly lick it. Birds with sharp bills such as warblers pierce the bottom of the flower in order to release the stored nectar so it can be drunk easily. Birds with sturdier bills, such as finches, nibble at the flower, crushing the bloom and releasing the nectar that way. No bird has a diet exclusively of nectar since it contains no proteins and essential minerals. So nectar eating birds also eat insects. Fruit eaters Fruits like apples, cherries, grapes and plums are liked by all, including birds! They are an excellent source of sugar, especially during breeding and migration. Of course, they can be a pest to fruit farms. Birds like the red whiskered bulbul and jungle myna are particularly fond of fruit. However in the tropics, almost all birds will eat some fruit. Fish catching birds These are very common around water bodies. The most common is the kingfisher. The water birds catch their prey in the water or near the shore, while some birds stalk their prey from the air. Dip Netting You must have seen (at least photos of) a pelican with their funny shaped beaks. They have a long straight upper jaw, often with a small hooked end, and a lower jaw that looks like a pouch. It is adapted to hold a large fold of skin that is used like a net to trap fish when they gulp water. The water is drained off and the catch is then swallowed. Surface skimming birds The Indian Skimmer is a black-and-white bird with a bright orange beak. It has a lower jaw that is much longer than its upper portion of beak. The bird uses this to skim the water surface, and scoop up its prey. It is an endangered species. Scything Some wading birds like the pied avocet use their bills in mudflats and wetlands to catch small insects. They catch them by sweeping their long, thin, upturned bill through the surface waters or mud. Filter feeders Some birds like the lesser flamingo filter the water in which they scoop up fish. Their bills are therefore adapted to this form of feeding. Aerial Bird Adaptations Aerial birds have slender, streamlined bodies and long wings that maximize flight efficiency, along with unusually lightweight skeletons and other adaptations for easier, lengthy flight. Some of them eat insects while others eat fish. Aerial fishers The kingfisher is the most common of aerial fishing birds. It hovers above the water until it spots its prey, and then swoops in a spectacular vertical dive to capture the fish. Some species of aquatic birds chase fish by diving from the surface of a pond, lake, river or sea. Inectivorous birds Many birds catch both insects and fish. Ground feeding birds catch their prey by gleaning them from the foliage or ground where they are found. You may have seen some birds pick off insects from larger animals like cattle. Those species that seek pest insects are considered beneficial to humans. It is estimated that insectivorous birds eat 400–500 million metric tons of arthropods (insects, spiders, etc) annually. Chiseling Birds with chiseling beaks are wrens, woodpeckers and warblers. The chisel-shaped beaks are strong and sturdy with a chisel-like tip (like a broad screw-driver). The birds use these to drill holes into tree barks, to catch insects and eat. You must have heard woodpeckers pecking away loudly for long periods of time. Have you wondered why they don't get headaches?! Hawking and flycatching When birds catch a flying insect in the air, it is called hawking. Such birds like bee eaters (shown with a bee in the picture) return to their perch with their prey. Some birds spend almost their entire lives flying, so they are called flycatchers. Birds like swifts and swallows also catch insects while flying and are called aerial feeders. Many birds have a combined strategy of both hawking insects and gleaning them from foliage. Apart from wing size and shape, bill size and shape is also important. Compared to the bills of birds specialized for gleaning, a relatively larger, broader bill and a wide gaping mouth is ideal for catching sizeable insects such as bees and flies. Their long wings allow swifts to spend virtually their entire lives in the air (some non-mating common swifts have spent as much as 10 months in the air without landing). They rely on insects as their main source of food. Scavenging Birds Scavenging birds are birds like vultures that feed on dead and decaying flesh. They are important to keep the environment clean and prevent spread of disease due to rotting carcasses. Raptors Birds like hawks that hunt and kill other animals are called raptors. The most famous is the tawny eagle, which is under threat in India. They mostly target live prey that is on the ground; sometimes they fly down and take birds on the wing. The term "hawking" comes from the similarity of this behavior to the way hawks take prey in flight. Whereas raptors may catch prey with their feet, hawking birds catch insects in their bill. Next time you see a bird feeding, observe how and what it eats. There is such a variation and complexity in this seemingly simple activity. Acknowledgement: This article is adapted from numerous fascinating internet sources, especially Wikipedia and https://www.thespruce.com.