Aves - Birds - Animalia

Kingdom - Animalia
    Phylum - Chordata
        Subphylum - Vertebrata
            Class - Aves

Basic Features:

Aves is a Class in the Subphylum Vertebrata of the Phylum Chordata, so they have all of the characteristics of both of these groups in addition to the following:

• Waterproof skin covered in feathers
• Endothermic, warm blooded
• Hard shelled eggs that are waterproof (cleidoic - closed egg)
• Beak or bill rather than teeth
• Bipedal (walk on two legs only)
• Forelimbs developed into wings
• Most members are highly adapted for flight with forelimbs modified as wings and many weight saving features such as hollow bones

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What do birds eat?

You would expect such a widespread and varied group as the birds to include members that eat most things. This is largely true, though there is usually one common factor to the food eaten by birds and that is that it is high-energy.

Birds have the highest body temperatures of any animal with the highest metabolic rate in terms of energy needed per gram of body mass.

This means that they can't afford to waste time eating bulky low energy foods as they wouldn't be able to be so active. It also means that they need highly concentrated energy foods in order to still be light enough to fly. Birds can't keep food in their digestive systems for long as the weight would soon build up and make flight very difficult. There are no bird equivalents of cows or sheep for instance.

As examples of the energy needed, a warbler (small songbird) might eat 80% of its own body weight a day, while a shrike can digest a whole mouse in three hours.

Generally speaking food from an animal source, invertebrates, fish, small mammals, other birds etc. is more nutritious than much plant derived food.

Birds that do eat plant material eat the higher energy parts such as seeds, nectar and fruit rather than leaves and stems. Those birds that do eat leaves tend to be very selective choosing only the most tender nutrient dense ones that are the easiest and quickest to digest.

One herbivorous bird, the Canada Goose removes the easy to get at nutrients from grass that it eats and then rather than further digestion to recover more nutrients, it defecates it out and then eats fresh grass. The faecal pellets so produced may be eaten by reindeer such is their remaining nutritional content.

Another unique aspect of the way that birds feed is that they have a beak or bill and no teeth, most food is swallowed more or less whole and not chewed in the way that other animals might. The digestive systems of birds are very efficient with a gizzard to grind up the food and very aggressive digestive enzymes.

Birds eat fish, squid, worms, grubs, ant and termite eggs, other birds, small mammals, snakes, lizards, frogs, toads etc. any animal smaller than them that they can catch.

They may eat fruit, seeds, unopened flowers, young leaves, buds, nuts, and other concentrated energy easy to digest plant material.

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What eats birds?

Catching birds to eat is not easy because they can quickly fly away. However while flight enables them to escape predation it also puts them in the way of predation.

Flight requires birds to be lightweight, so when they reproduce, they carry the young for as short a time as possible. The fertilized egg with a very large food supply is produced. This means that birds are tied to their nests in order to reproduce which makes them very vulnerable to predation at this time. So what eats birds?

• Predatory birds such as falcons, eagles, hawks and owls eat other birds.
• Domestic cats eat birds, catching hundreds of millions a year world-wide, perhaps billions.
• Some unexpected animals like large spiders, frogs and toads eat small birds.
• Mammalian predators such as stoats, weasels, raccoons, jaguars, foxes, lions, tigers, and bears will eat birds especially if they can catch them on the nest where even if they don't catch the adults, there are likely to be nestlings or eggs to eat.
• Seals, sharks and large fish eat water-birds.

Birds are often in the middle to the top of food chains being both predator and prey to different animals.

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The group includes:

Possibly more than any other animal group, the birds are the easiest to identify and the least likely to be mis-identified. The combination of the obvious characteristics of  bipedalism, a beak and feathers is unmistakable. There are around 10,000 species of birds arranged in 29 orders, some examples are given here:

• Anseriformes - waterfowl, web-footed for swimming - ducks, geese, swans
•  Apodiformes - "footless" in Latin (they do have feet though), legs are used for perching and have no scales as other birds do - swifts, hummingbirds
• Cathartiformes - large scavenging birds, usually have a bald, featherless head - New World vultures or condors
• Charadriiformes - usually found around water, frequently the sea - gulls, auks, plovers, terns
• Columbiformes - the only birds capable of drinking by sucking without having to tilt the head back, able to produce "crop milk" to feed the young - doves and pigeons
• Falconiformes - raptors,  sharp hooked beak, strong legs and feet with strong claws - falcons, eagles, hawks
• Galliformes - fowl, ground feeding, heavy bodied birds, usually able to fly but only for short distances, walk to get about - chicken, turkey,  grouse, pheasant, ptarmigan
• Opisthocomiformes - young possess claws on two of their wing digits (fingers), a very primitive feature - a single species the hoatzin
• Passeriformes - songbirds or perching birds, usually smallish birds, more than half of all bird species are in this order - sparrows, crows, drongos, birds of paradise, larks, swallows
• Pelecaniformes - water birds that feed on marine life, webbed feet, some have a large throat pouch - pelicans, cormorants, frigate birds
• Phoenicropteriformes - long-legged, long-necked filter-feeding waders - flamingos
• Piciformes - mainly tree-dwelling, feet have two toes forwards, two backwards - woodpeckers, toucans,
• Procellariiformes - tubenoses, most feed in the open sea, nostrils in tubes, nasal gland to secrete excess salt, long narrow wings, webbed feet - albatrosses, petrels
• Psittaciformes - mostly tropical and subtropical, strong curved bill, upright stance, strong clawed feet, often bright or vivid colours - parrots, macaws, cockatoos, parakeets
• Sphenisciformes - aquatic flightless birds found in the southern hemisphere only as far the equator - penguins
• Strigiformes - sharp hooked beak, strong legs and feet with strong claws, large forward-facing eyes in a characteristic and obvious circle of feathers, binocular vision, the eyes can't move in the socket so the whole head moves - owls
• Struthioniformes - ratites, large flightless birds, no "keel" on the breastbone (sternum) which is used in other birds attach their flight muscles - ostriches, emus, kiwis

The smallest bird is the bee hummingbird at 5.7cm (2.25in) long and 1.6g (1/18th of an ounce).

The largest bird is the ostrich at over 2.7m (9 feet) high, weighing 156kg (345lb), this is 97,500 times heavier than the smallest bird.

The largest wingspan is that of the wandering albatross with a measured maximum of 3.63m (nearly 12 feet).

The commonest bird is the domestic chicken as it is reared for food, there are around 4 chickens for every person on earth which comes to 25 billion + chickens. Of wild birds, the European house sparrow is thought to be the most common being found on about 2/3 rds of the land surface. A small songbird, the red-billed quelea is thought to be close in numbers with a population of 1.5 billion though is confined to sub-Saharan Africa.