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Birds Classification Study Guide

Animal Biology

What are the distinguishing traits for different classes of vertebrates? No idea? Don't worry! We've got your back. Engage with our study guides and interactive 3D models to recognize these traits.

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## Introduction
Birds are __[vertebrates](https://www.inspiritvr.com/general-bio/vertebrates/vertebrates-diversity-evolution-classification-and-reproduction-study-guide "vertebrates")__, having a vertebral column and a skull. These warm-blooded animals have feathers, and their forelimbs are modified to form wings. Birds were the last vertebrates to evolve, but they increased and diversified in no time. Today they are the most numerous vertebrates on the earth (number & species). We have birds as tiny as 5 cm and as large as 9 feet surviving strongly. 

### Bird Structure
Birds have different anatomy. Somebody parts of birds are different than that of other animals. This is a result of several structural adaptations, making them more sustainable.

![Anatomy of a Bird](//images.ctfassets.net/4yflszkpcwkt/3cQ4TSGiU2l7PkIpJPyU1D/71480927ed9f542e4087a84c2fafdeaf/il_794xN.1861404527_lvre.jpg)
[Source](https://www.etsy.com/listing/677297406/bird-anatomy-print-c-1937-bird-diagram?show_sold_out_detail=1&ref=nla_listing_details)

__Wings__

- The most distinctive feature of the birds is their wings. Wings are their modified front legs. To move these wings, birds have very strong and large in their chest. These muscles contribute to about 35% of the bird's weight. 

- The main function of the bird's wings is to provide them with the ability to fly. All birds have two wings, but that does not imply flying. The terrestrial birds which can't fly have very small wings, and some birds like penguins use them as flippers.

__Feathers__

- Feathers are a chief distinguishing feature of birds. Bird's feathers are made up of keratin and have many functions. The most important being helping them to fly and to insulate their body. 

- There are two types of feathers for each function- Flight feathers and feathers. Flight feathers are stiff, long, and waterproof. Without adding weight, they help in flight, whereas the down feathers are short and fluffy and help insulate the body by trapping the air next to the bird's skin.

__Beak__

- Like other vertebrates, birds don't have dense and heavy jaws and teeth. Instead, they have keratin beaks. It is an example of structural adaptation for flight in birds, and the flight would not have been possible if birds had . 

- The shapes and sizes of beaks vary with different birds, but they all have a similar underlying structure. The main function of the beak is to eat, preen, feed their young ones, collect things, attack their prey and defend themselves.

__Feet__

Feet of the bird are generally covered with scales.
There are predominantly two major types of feet present in the birds. 

- Three toes are directed towards the front and one at the back. They are very powerful, with sharp, curved talons used to catch, hold and kill prey. Owls, Hawks, Eagles have such feet.

- The other common feet structure have a web between three front toes, providing an expanded surface for swimming and walking on soft surfaces. These kinds of feet are generally seen in seagulls, ducks, etc.

### Organs of the bird
The body of a bird has to be very light to stay aloft. Thus, nature has provided them with such an organ system that serves the purpose, and all the bird's body parts contribute towards that.

![Bird Organs](//images.ctfassets.net/4yflszkpcwkt/69SczM4hQcujPVlRxZNp3h/a0dc332513b7bcafc19a292a4a864299/anatomy_bird_color_poster72.jpg)
[Source](https://www.exploringnature.org/db/view/Bird-Anatomy-Poster)

__Bones__

- The bones of a bird are generally very lightweight and filled with air. A bird's skeleton is very lightweight because of the thin and hollow bones and thus does not add to the bird's overall weight, hence helping in their flight.

__Air Sacs__

- The flying muscles of birds need a constant oxygen supply. To ensure this, nature has provided them with air sacs that store inhaled air and push it to the lungs, hence, keeping the lungs always filled with oxygenated air. 

__Heart__

- Birds have a large __[four-chambered heart](https://www.inspiritvr.com/general-bio/human-biology/heart-study-guide "four-chambered heart")__. The size of their heart is 0.2%- 2.4 % of their body weight, which is quite high compared to other mammals. Birds also have relatively high heart rates, which help them to keep a constant flow of oxygenated blood to muscles and other tissues.

__Digestive tract__

- The two important parts of a bird's digestive tract are- Crop & Gizzard. The crop is a sac-like part used to keep and moisten food before digestion, whereas Gizzard is used to store the swallowed stones, which help digest the food more quickly. 

__Brain__

- Generally, birds have a big brain compared to their body size, which accounts for their intelligent and complex behavior. Ravens & Crows are said to have more intelligence than many mammals.

__Kidneys__

- The bird's kidneys lie on the underside of the pelvis.

__Urinary Bladder__

- Birds do not have a bladder, and urine is secreted with the feces. 

__Sight__

- Birds have excellent sight, making up for their low sense of smell.

### Conclusion
- Birds have evolved, and with the help of many structural adaptations, today they are the most occurring (in numbers & species) and sustainable vertebrates on the earth.

- The organ system of the birds is highly adaptive to their flight. The skeletal system, circulatory system, respiratory system are such that they aid the bird's flight.

- Birds have a relatively larger heart and a large brain, and their intelligence is found more than many mammals.

### FAQs
__1. What structures help the birds get and eat their enemies?__

Ans. The bird's beak and feet are the two structures that help them get and eat their enemies. Every bird has a distinctive, adaptive beak and feet structure according to its habits and habitats.

__2. What is the structure of a bird's bones?__

Ans. Bird's bones are hollow and thin, filled with air.

__3. What are the structural adaptations in birds?__

Ans. The major structural adaptations in birds are
Beaks instead of heavy jaws and teeth.
Feathers instead of heavy fur. Feathers are lightweight, streamlined, and adjustable for flight control.
Pneumatized (hollow) bones keep the body of birds lightweight.

__4. What is a bird structure?__

Ans. Birds have a light skeletal system and light yet strong muscles. They have a circulatory and respiratory system that gives them a high metabolic rates and abundant oxygen supply to help them with their flight. 

__5. What are 5 examples of structural adaptations?__

Ans. The 5 examples of structural adaptations in birds are-
- Webbed feet 
- Beaks
- Hollow bones
- Sharp eyesight
- Feathers

__6. What is the function of a bird's wing structure?__

Ans. The function of a bird's wing structure is similar to that of human arms. Wings in birds adapt to flight, and they are the modified front legs. With the help of strong chest muscles, birds use their wings to fly.

__7. What is the function of a bird's beak?__

Ans. The main function of a bird's beak is to eat and preen along with gathering & catching prey, feeding their young ones, picking materials for the construction of their nests, and sometimes to defend themselves.

*We hope you enjoyed studying this lesson and learned something cool about __Birds- Structure, and Function__! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App to experience our fun, VR classrooms - we promise, it makes studying much more fun!* 😎

## Sources
1. Bird Structure and Function [https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/12.19/primary/lesson/bird-structure-and-function-bio/](https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/12.19/primary/lesson/bird-structure-and-function-bio/) accessed on 6 Dec 2021

2. Bird anatomy [https://en.wikipedia.org/wiki/Bird_anatomy](https://en.wikipedia.org/wiki/Bird_anatomy) accessed on 6 Dec 2021

3. Bird Classification [https://www.britannica.com/animal/bird-animal/Classification](https://www.britannica.com/animal/bird-animal/Classification) accessed on 6 Dec 2021

Bird - Structure, and Function Study Guide

Fish: Structure and Function Study Guide

## Introduction
Reproduction of birds is a key process through which birds create new individuals, perpetuate the species, and transmit their genes. Birds' reproduction is not similar to other animals in a lot of aspects. Their anatomy itself is different where most males do not have external genital organs, and females reproduce with just a single ovary (usually the left ovary). The other aspects of aves reproduction include an increase in the size of sexual organs, hormone production, and other ethological parts like how birds mate, territorial behavior, and their exhibition of pairs.

### Do Birds Reproduce Sexually or Asexually? 
Are birds asexual? Asexual reproduction is not yet known in avian species, but a single bird can become reproductively active and lay an unfertilized egg in its lifetime as a captive. Birds reproducing an offspring starts by laying eggs. 

### Bird sexual reproduction
- The process of how a bird gets pregnant begins with a bird finding its pair to mate.

- A male bird generally presents signals like songs and calls to attract a female bird.

- After a pair forms, it is the end of the courtship period and the copulation period.

- Both male and female birds have a cloaca, the single exit and entry point for eggs, sperms, and waste matter.

- The ways birds mate and their position while having sex vary from one species to another. But in most cases, the male bird balances on top of the female bird to copulate, and both males and females face in the same direction.

- Then the female bird moves aside her tail to expose her cloaca, and the male will curl or arch his body to rub his cloaca against the female’s cloaca.

- The rubbing (also known as cloacal kiss) lasts for less than , and the sperm is quickly transferred, and the mating is completed.

- The sperm then travels through the oviduct and reaches the , fertilizing the egg.

- The hard-shelled egg develops inside the female bird.

- The eggs are then incubated by the bird that provides heat to the eggs with the help of its brood patch. Incubation can be done by both male and female birds.

- The incubation period can last from 10 to 80 days, depending on the species.

- After the embryo has fully developed inside the egg, hatching occurs where the beak breaks the eggshell of the baby bird.

![Reproduction in Birds](//images.ctfassets.net/4yflszkpcwkt/71ibIJySUXZDHl4HDcYXmx/1b71a348c624340943a4c52579bc1f42/2722102_orig.jpg)
[Source](http://theblackcappedchickadeeresource.weebly.com/uploads/1/7/0/8/17080078/2722102_orig.jpg?567)

### Courtship in Birds
The courtship period in birds can last much longer than actual copulation. Birds try to charm their partner in many ways and signals, visual and auditory. In the courtship period, the male bird tries to showcase his strength and health to female birds to convince them that they are the best mate.

The courtship period can have many stages, which begin with claiming territory to wooing a prospective mate. Some of the signals and acts performed by birds to woo a partner are:

- Intricate songs and calls.

- Vibration of feathers

- Drummings displays

- Air sacks and spectacular flights.

- Extravagant crests.

- Dances

- Aerobic flights.

- Moving wings and tails.

- Offering nests or nests sites and food.

![Courtship in Birds](//images.ctfassets.net/4yflszkpcwkt/4xJ4UafaY2QnVwV3uf2CFE/6c8f36e6ee2485600f80c8fab28abaef/robin-courtship.jpg)
[Source](https://www.birdspot.co.uk/bird-reproduction/courtship-behaviour-in-birds)

### Establishing Territory
Once birds form pairs, most of the species establish a territory where the bird defends against other species. The territory is chosen to protect from predators and with sufficient food resources. The birds build their nest and raise their young in this territory.

- The size of the territory depends on the birds' species, their size, and their needs. For instance, raptors need , and passerines build small territories.

- The pair forms a small territory around the nest. In some birds like seabirds form large colonies. The incubating bird defends the nest while the other partner looks for food.

- In most species, the territory is defended by the male though there are some species where females also defend the territory.

## Conclusion
- Birds reproduce sexually where males and females go through a period of courtship and then copulation. 

- The transfer of sperm to the ova happens through the cloaca, which is present in both males and females. 

- In general, birds are , and both parents take care of their offspring together.

### FAQs
__1. How do birds reproduce sexually?__

During mating, the male bird goes on top of the female, facing the same direction. They have an entrance called cloaca which they rub against each other. From the cloaca, the male sperm passes onto the female ova, where it is fertilized. After fertilization, the egg comes out of the female cloaca.

__2. Do birds have penises?__

Most male birds do not possess a penis apart from some waterfowl like swans, ducks, ostriches, and geese. The embryo does develop a penis, but it disappears once the egg hatches. The gene called Bmp4 is responsible for the missing penises in birds. Due to this gene, the cells at the tip of the penises of birds die faster than they grow back.

__3. How often does a bird reproduce?__

In general, birds nest once a year but certain species such as American Robin can nest four or five times in a single breeding season.

__4. How long is a bird pregnant before laying eggs?__

The incubation period in birds varies hugely from species to species. The egg may be laid within a few days or take several months before eggs are ready to be laid.

__5. Do birds reuse nests?__

No matter how clean their nests are, most birds do not reuse their nests. A bird builds a new nest for each clutch in a new location, and building a new nest reduces parasites and lice that lay eggs in the nest materials.

__6. Do birds lay unfertilized eggs?__

Apart from domesticated chickens and other pet birds, none of the wild birds lay unfertilized eggs. The eggs laid by domesticated birds are infertile and do not hatch.

__7. How long is the mating season for birds?__

Most of the residential species of birds start mating in spring so that the breeding season falls between mid-June and September. They prefer this period for breeding so that their young ones are not exposed to too hot or cold climates.

*We hope you enjoyed studying this lesson and learned something cool about the __Bird- Reproduction__! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App and check out our awesome VR room for this guide - we promise it makes studying much more fun.* 

## Sources 
1. Bird Reproduction. [https://www.ck12.org/biology/bird-reproduction/lesson/Bird-Reproduction-MS-LS/](https://www.ck12.org/biology/bird-reproduction/lesson/Bird-Reproduction-MS-LS/). Accessed 3 Dec, 2021. 

2. How Do Birds Mate?. [https://www.thespruce.com/how-do-birds-mate-386108](https://www.thespruce.com/how-do-birds-mate-386108). Accessed 3 Dec, 2021. 

3. Bird Reproduction. [https://avianreport.com/bird-reproduction/](https://avianreport.com/bird-reproduction/). Accessed 3 Dec, 2021. 

4. Bird Reproduction. [https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/12.20/primary/lesson/bird-reproduction-bio/](https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/12.20/primary/lesson/bird-reproduction-bio/). Accessed 3 Dec, 2021.