Class Aves

What is a "Bird"?

  A bird is a two-legged, bipedal vertebrate that is distinguished from others by having feathers. Another distinguishing factor is that all birds have wings and most use these wings to fly. Birds give birth by laying eggs, from which live babies hatch. Beaks or bills are another characteristic that is found on all bird. There are currently over 9,000 species of birds living on Earth with over 2,217 genera. 

 

Phylogeny and Evolution

       Birds have been on Earth for millions of years. Most scientist and people think, and what most theories are pointing to, that birds evolved from bird-like dinosaurs. In the 1800's, in Germany, a fossil called  Archaeopteryx was discovered. While it was a dinosaur, the fossil was more bird-like in structure, as it had bird-like feet, a wishbone, and feathers. This lead scientists to the conclusion that modern birds evolved from dinosaurs like Archaeopteryx. 

      Birds have adapted themselves over millions of years to be able to fly. Hollow bones were adapted to make them lighter, and therefore more aerodynamic and faster. Another adaptation is the air sacs in there body that connect to their lungs. Since Birds need more power to fly, they need more oxygen, which is where the air sacs come in.


Here is a modern Phylogeny Tree for birds.

 

Taxonomy

   Birds belong to the kingdom Animalia, the phylum Chordata, and class Aves. 

    Here is a list of the orders of birds and what type of birds are in this order:

Struthioniformes: ostriches, emus, kiwis, and allies
Tinamiformes: tinamous
Sphenisciformes: penguins
Gaviiformes: loons
Podicipediformes: grebes
Procellariiformes
Pelecaniformes: pelicans and allies
Ciconiiformes: storks and allies
Phoenicopteriformes: flamingos
Anseriformes: waterfowl 
Falconiformes: falcons, eagles, hawks and allies 
Galliformes: fowl 
Gruiformes: cranes and allies
Charadriiformes: gulls, button-quails, plovers and allies
Pteroclidiformes: sandgrouse
Columbiformes: doves and pigeons
Psittaciformes: parrots and allies
Cuculiformes: cuckoos and turacos 
Strigiformes: owls
Caprimulgiformes: nightjars and allies
Apodiformes: swifts and hummingbirds
Coliiformes: mousebirds
Trogoniformes: trogons 
Coraciiformes: kingfishers and allies
Galbuliformes: Jacamars and Puffbirds
Piciformes: woodpeckers and allies 
Passeriformes: passerines

 

Habitiat

    One of the most amazing things about birds, in my humble opinion, is how well they can adapt to their surroundings. And because of this, birds can be found on all 7 continents on Earth in any kind of biome. 

    Some Examples:

In woodlands, you kind find owls, sparrows, falcons, eagles, and warblers.

A Chestnut-sided Warbler: A Woodland Bird From Glorious Canada
In wetlands, you can find all kinds of birds such as ducks, herons, storks, among many other water fowls.

 
A Shoebill. I love this beak.


Grassland, Savannah, and Prairie birds include grouse, pheasants, Ostriches, and some other small birds.

A Prairie Chicken.  Those are some REALLY strange eyebrows.

The desert is also a home to many birds like vultures, some quails, Roadrunners, and hawks. 

The Roadrunner. Fast and nothing like it's cartoon counterpart.

Seabirds include seagulls, pelicans, puffins, and terns. 

An Albatross, one of the largest sea birds. Doesn't come with wafers.

The tropics have a list of many bright and colorful birds like macaws, parrots, and toucans, just to name a few.

A quetzal is a tropical bird from Mexico. It is also ridiculously cute.

In the frozen tundra, arctic, and taiga, birds such as penguins, owls, and terns make their home here.

An Arctic Tern. 

 

Digestion and Excretion

    Not present in all birds, after digesting food, most birds transfer this to the crop, a storage device for soon-to-be-digested food. When a bird is resting and digesting it's food, the crop refills the stomach with the food it has collected.

    The bird has a two-chamber stomach. The proventriculus, being  the first chamber. It's job is to secrete food with acid, to help break it down, and is best developed in birds that swallow it's food, such as fish, whole. The gizzard is the toughest chamber of the stomach because it's function is to grind and digest really tough food. But muscles are not able to do it alone. Sometimes, birds pick up and swallow small rocks or grit which helps pulverize the food and breaks it down. 

    From the stomach, the food travels through the intestines, where nutrients are absorbed and wastes are eventually excreted out of the system.

    Also found in the body, are the caeca, where they aid in the absorption of water and proteins and the microbial decomposition of fiber.

    Finally, the cloaca is where waste from the digestive and urinary tract accumulate before being dumped

Reproduction

    Like mammals, avian reproduction begins when an egg, or ovum, is fertilized in the oviduct by contact with a sperm cell. In birds, this is done when both the male and female's cloaca press against each other during coitus (called the "cloacal kiss") and the sperm moves from the male to the female.
    
    The fertilized egg will soon develop with a food source (yolk) and a casing (shell) surrounding the nucleus of the egg. After this has been developed, the female will lay the egg. Something else to note, most domestic birds, such as chickens and ducks, will lay eggs even if they are not fertilized. These eggs are used for commercial goods, and are the eggs that are available at stores.

    Because birds need to be as light as possible for flight, special adaptations have been made to ensure that the organism can fly, and yet still be able to reproduce. For instance, the male's testes only grow when producing sperm; where they become several hundred times bigger, giving new meaning to the term "Big Balls". The female's ovaries also swell when producing an ova for the breeding season.

Circulatory System

    Birds have a closed circulatory system, which is common in every vertebrates. They also, like a mammalian heart, have four chamber hearts, with two atria and two ventricles, with no mixture of venous and arterial blood. However, the aorta curves down to the right in birds, while in mammals, it curves down to the left.

Nervous System

    The spinal cord is found in all vertebrates, and is part of the central system and acts as the brain's "messenger", relaying decisions that the brain makes to the muscles that correspond to the "message". 

    Birds have a three part brain, composed of a section for the bird's olfaction, optics, and hearing. 

    Cladisticly new in bird brains is the hyperstriatum. This section is associated with the intelligence of the bird, and smarter birds will have larger hyperstriatums.

Body Plan, Structure, Movement, and Symmetry

    Birds have a really unique body plan and an incredible way to move around. While other animals swim, run, walk, or crawl to get to their destination, birds are the only animals aside from bats to have evolved the ability to fly. And because of this adaption, birds have adapted their bodies in order to fully be able to do this.

    Most birds are designed to be as light and aerodynamic as possible. All birds have wings, which enables some to fly. (Other birds, such as penguins, emus, and kiwis are flightless, but still share most of the qualities as birds who can fly.) As birds flap their wings, air is pushed down lifting the birds up in the air. The wings are curved, as to create the needed angle in which the air is pushed down, giving lift. 

    Birds have also evolved feathers, which is perhaps their most useful adaption as they assist in warming the bird and helping it's flight.

    Other adaptions birds have made include a really light body. Birds need to be as light as possible in order to fly. One of these adaptions is hollow bones. 

    Birds are bi-lateral symmetrical.

Respiration

    Like mammals and reptiles, birds have lungs, but they alone have air sacs. They're about 7-9 air sacs in a bird depending on the species. This includes two posterior thoracic, two abdominal, two anterior thoracic, two cervical (these are not present in some species), and one interclavicular. These sacs extend to the humerus, the femur, the vertebrae, and even the skull. And since birds do not have a diaphragm, they instead, move air in and out of the respiratory system through pressure changes in the air sacs. 

    It should also be noted that birds have two respiratory cycles instead of just the one in mammals.

Defense

    While flight is always an option, some birds have actually developed some other ways to defend themselves.



    The burrowing owl, when threatened, is able to mimic a rattlesnakes rattle to turn away predators.

    
    The hooded pitohuis is one of the few poisonous birds in the world. By eating certain beetles, it can excrete the poison onto it's skin and feathers.


    
    The potoo uses camouflage to escape predators by staying completely still and blending in with the tree bark.

 

Communication

    Birds use a variety of different methods to communicate with one another. One of the most obvious is with vocal calls. In mammals, it's the larynx that functions as the "voice box". While birds have a larynx too, it is not used to make sound. Instead, it is the syrinx that is used to make noises. The syrinx generates sound when the contraction of muscles (thoracic & abdominal) force air from air sacs through the bronchi & syrinx. 
Here is a video of a bird using the syrinx to "sing":

Common Loon Calling



https://youtu.be/Hw1It3AlX



Some birds use their environment to use as calls. 

Woodpecker Pecking at Wood



https://youtu.be/hAZgKanSm1c



    But by far, the most amazing use of communication, at least to humans, lies with the parrot. This is because parrots can learn to mimic human speech. They do this by controlling muscles in their throat to direct air in such a way that it can mimic certain tones and sounds. In some cases, there have been parrots who are smart enough to learn how to carry conversations. 

 

Interesting Facts

1. The only wingless bird in the world is the kiwi.

2. Falcons are able to swoop down at speeds up to 200 mph.

3. Penguins and Ostriches (and relatives) are the only two kinds of living birds that do not fly. 

4. The ostrich egg is the largest living bird egg on Earth. To hard-boil it, it would take up to 2 hours.

5. A bird's heart beats 400 times per minute while resting and up to 1000 beats per minute while flying.

Three Specific Species

Snowy Owl - Nyctea scandiaca

    Snowy Owls are a special species of owl, as they are white and live mostly in cold climates, being partial to the Arctic Circle during summer, and Canada and the northern United States in the winter. They can grow up to 20-28 inches with a wingspan of 4.2-4.8 feet, and mostly eat lemmings as well as other small mammals, birds, and fish. It also has the unique distinction of being the official bird of Quebec.                   


Because Rush wasn't awesome enough, they went ahead and put a Snowy Owl on their album cover.



Kakapo- Strigops habroptila

    The Kakapo is the world's only flightless parrot as well as the heaviest at 4 kilograms. It is only found in New Zealand and is one of the most endangered animals on the planet with about 126 still left in the world.  These parrots are also herbivores that feast on fruit, almonds, and stems of plants. 

This video is from the BBC reboot of Douglas Adams's Last Chance To See, a radio show in which he went around the world to take a look at endangered animals. This reboot, hosted by Stephen Fry, took a look at the animals that Adams examined to see how they are getting along since Adams saw them in the 1980's, and one of these animals is the Kakapo.

https://youtu.be/Opv8vZ6RvB0

 

Adelie Penguin- Pygoscelis adeliae

    The adelie penguin is perhaps the most familiar species of Antarctic penguins; it is also one of the smallest,

 being about 8-12 lbs and can be as tall as 18-24 inches. Like all penguins, it is flightless, but makes up for it by

 being a great swimmer. Adelies usually live in colonies of 200,000-300,000, with a total estimated population of

 4-5 million. Adelies feed on krill and small fish. 

 

 

 

 

Outlook

    There are over 9,000 known species of birds in the world right now. 1,253 of these are endangered with 4 species extinct in the wild. 

    Birds are preyed upon by many animals including, mammals, reptiles, other birds, and man.

    One of the best reasons why some birds are endangered is because of man's intervention. Aside from habitat destruction, the hunting of birds is one of the biggest things man has done to birds. Man hunts birds for a variety of reasons: sport, food, and even for a bird's feathers and other body parts.

 

Links

1. Birds: http://www.birds.com/