Pigeon (Chordate)


external image pigeon&sa=X&ei=LLXCUK37Eo6w0AGB4IGABA&ved=0CAkQ8wc&usg=AFQjCNEmSyR0WYdn6oafZWWvetWmDUPbiA
By: Shreya Bhatia

Topics:

  1. Classification/Diagnostic characteristics

  2. Relationship to humans

  3. Habitat and niche

  4. Predator avoidance

  5. Nutrient acquisition

  6. Reproduction and life cycle

  7. Growth and development

  8. Integument

  9. Movement

  10. Sensing the environment

  11. Gas exchange

  12. Waste removal

  13. Environmental physiology (temperature, water and salt regulation)

  14. Internal circulation

  15. Chemical control (i.e. endocrine system)



Classification/ Diagnostic Characteristics


Pigeons belong to the kingdom Animalia, the phylum chordate and the class aves. Birds and crocodilians have common ancestry originating from dinosaurs. Birds, specifically, are thought to have originated from “therioids,” dinosaurs with traits such as bipedal stance (two feet), hollow bones, a furcula (wishbone—forked bone found in neck area of birds and such animals) elongated metatarsals (bones that make up our feet/ toes) with three fingered feet, elongated forelimbs with three-fingered hands, and a backwards pointing pelvis. Other major and distinctive characteristics pigeons have are that they hatch from eggs, have feathers, a beak, two feet, and wings (1).


Relationship to Humans


Pigeons were used to transport letters years ago. According to Mr. Snow, a biology teacher at Sharon High, Darwin loved pigeons. Pigeons are very well known for finding their home and destination even if they are in unknown territory. This ability to return to specific locations is called homing. Even though pigeons can do this by following the path of the sun, they do not always need the sun to find their way. Perhaps Darwin loved using pigeons to transport mail because of this natural and adept ability (1).

Pigeons are also in contact with humans when it comes to food. One often finds pigeons in cities, since cities are full of food, and pigeons love eating whatever food they can find. People often personally feed pigeons, perhaps out of pity or admiration for their looks. Because of this proximity, pigeons are not that afraid of humans, and can come to very close distances to us. Pigeons can also be used for research and experiments. For example, Charles Darwin bred pigeons in his study for artificial and natural selection (1).

Domesticated or hunted pigeon have been used as the source of food since Ancient Middle East, Ancient Rome and Medieval Europe. It is familiar meat within Jewish, Arab and French cuisines. According to the Tanakhm, doves are kosher, and they are the only birds that may be used for a korban, a sacred offering. Other kosher birds may be eaten, but not brought as a korban. It is also known in Asian cuisines, such as Chinese and Indonesian (2).


Habitat and Niche


Pigeons are located all around the world, especially in forests and coasts. They are mostly found in urban areas where there is a high density of humans, specifically in cities and parks where food is easily sought. Pigeons nest in trees near areas of easily available food. Pigeons usually eat worms, seeds, and human leftover foods from garbage and the ground.

Pigeons are eaten by large birds such as hawks, and animals such as cats and racoons (1).

Even though certain species are in a large abundance, a third of the 316 pigeon species are thought to be threatened, according to the World Conservation Union. These animals have very limited habitats, occupying only small oceanic islands. The passenger pigeon, for example, was driven to extinction by human hunting (3).

The original native habitat of the pigeon is cliff sides, and many can be found today nesting on eastern Washington on cliffs (4).




Predator Avoidance


Pigeons travel in large numbers to avoid larger predators such as Goshawks. Pigeons travel in large flocks because the more members they have, the higher the chance that one will see the hawk and fly away. When one member flies away, the other pigeons quickly disperse, making it difficult for the predator to target and attack one pigeon (1).


A Goshawk, predator of the pigeon.
A Goshawk, predator of the pigeon.
http://www.fs.fed.us/psw/topics/ecosystem_processes/sierra/bio_diversity/images/NOGO_adult_male_head.jpg


In addition to traveling in large packs, pigeons also use a common defense mechanism of birds known as the broken wing display that divert a predators attention away from a birds nest. Pigeons also have rather short nesting periods to avoid the chance that a predator can attack the nest (5).

boy chasing pigeons
boy chasing pigeons
Pigeons and squirrels not getting along.
Pigeons and squirrels not getting along.


Nutrient Acquisition


Pigeons are primary and secondary consumers, eating many types of seeds and worms, even insects. They get nutrients from their foods by digesting and absorbing the nutrients in the process. Since pigeons mostly live in human occupied spaces, they eat many foods leave behind by people. This can be deadly since pigeons may choke on large foods, or eat foods toxic to their bodies (1).



A pigeon eating food left behind by humans.
A pigeon eating food left behind by humans.


Because pigeons eat just about anything, they are very prone to health issues.
Because pigeons eat just about anything, they are very prone to health issues.
Pigeons may be bullies sometimes if they desire food.
Pigeons may be bullies sometimes if they desire food.

http://gothamist.com/2007/11/13/pol_wants_pigeo.php


Reproduction and Life Cycles
Affectionate pigeons.
Affectionate pigeons.


Pigeons are part of the avian family and thus, reproduce sexually and lay an egg from which the offspring hatches. The baby birds grow and develop and female birds begin giving birth after a few years. Their life span is about 11-15 years (1).

Pigeons can reproduce year round. During one year, a female may have up to five babies. The incubation period lasts for about sixteen to nineteen days. When the young hatch, they will be fed with crop milk for the first two weeks and then it is replaced by seed in a domestic environment (6).

When a hen, a female pigeon, lays her eggs, she sits on them to incubate them. During the day, the cock, the male pigeon, occasionally switches with the hen to incubate the eggs so that both parents are able to have opportunities to eat. The eggs must be kept warm at all times so that the embryos can develop properly within the eggs (7). [GW]

Growth and Development


Pigeons initially develop in the same way as humans do. When sperm from the male fertilizes the egg in the female, the egg begins to develop. That egg, called the zygote, goes through several cell divisions, known as cleavage, until a blastula is formed, which is made up of numerous cells. That blastula, in birds known as blastodisc, then goes through a process called gastrulation in which the blastula transforms into the embryo. Bird eggs have a lot of yolk, and so, their blastulas are flat and have a distinctive gastrulation process. After gastrulation, layers in the embryo are formed that soon differentiate into features and formations of the body that give pigeons their idiosyncratic characteristics (1). When the chick is well developed enough and grows so large that its shell cannot hold it comfortably, the baby pigeon breaks out of the shell. The chicks are quite helpless when young and rely on their parents to feed them. However, they are also able to stand and walk on their own just hours after hatching (8). [GW]

Integument


Pigeon’s protective covering consists of skin and feathers. There are many layers of skin and on top there are feathers with oil glands that serves as a barrier from water invading to the bird’s skin. Together the skin and feather barriers also protect the pigeon from pathogens entering the surface of the bird (1).
A close up of feathers.
A close up of feathers.
external image feather1.jpg




Movement


Pigeons have two legs and one set of wings, and they move with the help of bones, muscles, and tendons. The spinal cord, brain, and peripheral nervous system direct muscles to contract, which results in movement. There are different types of muscles that coordinate different types of movement. Cardiac muscle sustains heat beats, smooth muscle mostly directs involuntary movement deep within our bodies, and skeletal muscle is responsible for the bird’s voluntary movement. Muscles are especially important in pigeons since they are constantly in need of strong, dependable muscles when flying long distances (1).
A pigeon about to take flight.
A pigeon about to take flight.













Sensing the Environment


Pigeons are very apt at sensing the environment around them. Not only do they have piloting (storing and remembering the structure of the environment) and homing (finding the way home) which are very helpful when migrating and finding the way home from unknown territories, pigeons also have their own internal compass. Even if the sun is not out, they find their way to places since pigeons can sense Earth’s magnetic field. This is called having a “compass sense" (1).

Pigeons have many types of feathers, some of which are accompanied by one or two filoplume feathers that look like hairs. These filoplumes may have sensory functions, such as detecting touch and pressure changes. Pigeon eyesight is excellent. Like humans, pigeons can see color, but they also can see ultraviolet light – part of the light spectrum that humans can’t see. Pigeons are sometimes used in human search-and-rescue missions because of their exceptional vision. Pigeons can hear sounds at much lower frequencies than humans can, such as wind blowing across buildings and mountains, distant thunderstorms and even far-away volcanoes. Sensitive hearing may explain why pigeons sometimes fly away for no apparent reason (9).


Gas Exchange


Pigeons have a system of gas exchange unique to birds. Since birds require a tremendous amount of oxygen and energy for flights, they have a lung system that constantly supplies the birds with fresh air. Bird lungs, unlike human ones, decrease in volume when inhaling and inflate when exhaling. The bird has anterior and posterior air sacs. A major advantage of such evolution is that incoming air and deoxygenized air do not mix. The air comes in through the trachea (wind pipe) into the posterior sacs, which are at the back or lower part of the bird. Then, the air is pumped into the lungs so that the capillaries in the lungs absorb oxygen from the air. Next, the air from the lungs is pumped into the anterior sacs before it is exhaled out of the body. Birds, unlike humans, have two respiratory cycles. The two cycles occur simultaneously, which includes inhalation of air to posterior sacs and expiration of air to lungs for the first cycle, and inspiration of air to anterior sacs and expiration of air out of the body as the second cycle. This structure is efficient for absorbing oxygen from the air, and is necessary for birds since they fly in high altitudes and are in constant need of energy to maintain flight (1).


external image bird-airsacs.gif&sa=X&ei=jsXCUJjANuW-0QHUr4HgBA&ved=0CAkQ8wc&usg=AFQjCNH43wxOnTFsna-mCJSmM4kV0gpvNQ


Waste Removal


Pigeons are uricotelic animals, meaning they excrete uric acid as wastes. Since uric acid is not very soluble in water, bird waste is semisolid, including urine and the uric acid particles mixed together to produce the recognizable white color of pigeon droppings (1).
A pigeon removing waste on an unfortunate individual's cranium.
A pigeon removing waste on an unfortunate individual's cranium.
(Colin Gray)
http://www.arras.net/fscIII/wp-content/uploads/2007/06/PigeonPoopsOnGirl.jpg


Environmental Physiology (Temperature, Water and Salt Regulation)


Pigeons maintain homeostasis to maintain stable internal conditions. They are endotherms and thus maintain high and stable body temperatures. Because of this, they have high metabolic rates that keep them warm at constant temperatures, and thus require a lot of energy. Birds, since they are osmoregulators, maintain salt and water levels with the help of their excretory system. Pigeon excretions are made up of urine, which consists of extra water and salt, specifically sodium and chloride ions, the body needs to dispose. Thus, urinating regulates water and salt levels in the body (1).



Internal Circulation


Pigeons a have four chambered heart in which oxygenated and deoxygenated blood are separated. The deoxygenated blood is brought into the right atrium, one chamber of the heart, pumped into another chamber called the right ventricle, travels through the pulmonary artery to the lungs to be oxygenated. The pulmonary vein carries the oxygenated blood into the left atrium, another heart chamber. The blood is then pumped into the left ventricle, and finally carried by the aorta (an artery) to the body. Such circulation provides cells in the body with essential gases such as oxygen (1).

external image X+science+Blood+Circulation.JPG&sa=X&ei=XcbCUNm4FcaX0QGNtYCwAg&ved=0CAkQ8wc4fg&usg=AFQjCNEhzaud1fXqDJ5Jte9hOqgZmqPqfQ



Chemical Control (i.e. The endocrine System)


Pigeons have an endocrine system similar to that of humans that maintains blood sugar, metabolic rate, and many other processes in their bodies. There is a master gland, known as the pituitary gland, that controls the excretion of hormones in the body that are responsible for maintaining certain levels in the body (sugar, calcium, etc.), controlling reproduction by forming sexual organs and initiating sexual differentiation, and for regulating growth (1).

Pigeons are endothermic organisms that excrete hormones like calcium, glucose, and other substances to control the bodies metabolic rate, and other gland production rates. Also, their heart rate remains high because they are always being active due to the constant threat of having to run away/ fly away and they have a strange yet unique bone structure that allows them to fly with limited effort (10). (EK)

Important glands and organs in the pigeon.
Important glands and organs in the pigeon.



Review Questions


1. How are pigeons able to get around in the dark and migrate back and forth without getting lost or displaced?

2. What gland in the pigeon controls the excretion of hormones in the body that is responsible for maintaining, sugar calcium and other levels?

3. Describe the two respiratory cycles and explain the advantages of this structure.

4. Explain how the pigeon's waste removal system is advantageous when it comes to water and salt regulation.

5. How does the pigeon change, from the production of the egg to having parts with specific functions?

6. Explain the advantages of the pigeon's integument. How does this protect the organism from the temperatures at high altitudes?

7. What common defense mechanisms do pigeons posses that allow them to divert a predator's attention? (Alexander Soloviev)

8. How is the oxygenated and deoxygenated blood separated in the four chambered heart? (Cam Somers)

9. Explain the advantages of the pigeon's improved sight (ability to see larger range of wavelengths compared to humans). Give possible reasons of why this adaptation came about.

10. What adaptations do the pigeon's gas exchange and internal circulation systems have that allow them to successfully maintain homeostasis while being able to undergo strenuous activity such as flight?





Thank you for reading this wiki!
Thank you for reading this wiki!



Citations (Not including image citations)


1). Hillis, David, David Sadava, H. Craig Heller, and Mary Price. Principles of Life. High School ed. Sunderland: Sinauer Associates, 2012. Print.

2). http://en.wikipedia.org/wiki/Columbidae#In_religion

3). http://animals.jrank.org/pages/759/Pigeons-Doves-Columbidae.html

4). http://www.birdweb.org/birdweb/bird/rock_pigeon

5). http://animaldiversity.ummz.umich.edu/accounts/Columbidae/

6). http://www.pleasebekind.com/pigeon.html

7). http://bjornpigeons.webs.com/pigeonslifecycle.html

8). http://bjornpigeons.webs.com/pigeonslifecycle.html

9). http://www.pleasebekind.com/pigeon.html

10).http://classic.sidwell.edu/us/science/vlb5/Labs/Dissection_Lab/conclusions.html