Essay on migration of birds

What are the Major Effects of Light on Animals? The Major Effects of Light on Animals are as follows: The growth, colouration of plumage or body, migration, reproduction and diapause are affected by light in various insects, birds, fishes, reptiles and mammals. Many animals prefer to remain in dark, while others like hydroids fail to survive in absence of light.

Essay on migration of birds

These are the salmon spawning grounds where salmon eggs are deposited, for safety, in the gravel. The salmon spawning grounds are also the salmon nurseries, providing a more protected environment than the ocean usually offers.

After 2 to 6 months the eggs hatch into tiny larvae called sac fry or alevin. The alevin have a sac containing the remainder of the yolk, and they stay hidden in the gravel while they feed on the yolk.

When the yolk has gone they must find food for themselves, so they leave the protection of the gravel and start feeding on plankton. At this point the baby salmon are called fry.

At the end of the summer the fry develop into juvenile fish called parr. Parr feed on small invertebrates and are camouflaged with a pattern of spots and vertical bars. They remain in this stage for up to three years.

At this point salmon are called smolt. Smolt spend time in the brackish waters of the river estuary while their body chemistry adjusts their osmoregulation to cope with the higher salt levels they will encounter in the ocean.

When they have matured sufficiently in late spring, and are about 15 to 20 centimetres long, the smolt swim out of the rivers and into the sea. There they spend their first year as a post-smolt. Post-smolt form schools with other post-smolt, and set off to find deep-sea feeding grounds.

They then spend up to four more years as adult ocean salmon while their full swimming ability and reproductive capacity develop. Then most of them swim up the rivers until they reach the very spawning ground that was their original birthplace. One theory is that there are geomagnetic and chemical cues which the salmon use to guide them back to their birthplace.

The fish may be sensitive to the Earth's magnetic field, which could allow the fish to orient itself in the ocean, so it can navigate back to the estuary of its natal stream. Speculation about whether odours provide homing cues go back to the 19th century. They further demonstrated that the smell of their river becomes imprinted in salmon when they transform into smolts, just before they migrate out to sea.

They may also be sensitive to characteristic pheromones given off by juvenile conspecifics. There is evidence that they can "discriminate between two populations of their own species". InLeggett identified, as mechanisms worth investigating, the use of the sun for navigation, and orientation to various possible gradients, such as temperature, salinity or chemicals gradients, or geomagnetic or geoelectric fields.

Migrating salmon have been observed maintaining direction at nighttime and when it is cloudy. Likewise, electronically tagged salmon were observed to maintain direction even when swimming in water much too deep for sunlight to be of use. The quantities present are sufficient for magnetoception.

InQuinn hypothesized there is a dynamic equilibrium, controlled by genes, between homing and straying. However, if the spawning grounds have a variable quality, then natural selection should favour a mixture of the descendants that stray and the descendants that home accurately.

Fish swim by contracting longitudinal red muscle and obliquely oriented white muscles. Red muscles are used for sustained activity, such as ocean migrations.This essay delves deeply into the origins of the Vietnam War, critiques U.S.

justifications for intervention, examines the brutal conduct of the war, and discusses the . Abstract.

The advent of agriculture has ushered in an unprecedented increase in the human population and their domesticated animals. Farming catalyzed our transformation from primitive hunter-gatherers to sophisticated urban dwellers in just 10, years.

Essay on migration of birds

Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate.

Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where . Essay No. Pollution. The word pollution has been derived from the Latin word pollution, which means to make dirty.

Pollution is the process of making the environment land water and air dirty by adding harmful substances to it. THE NEW ORGANON OR TRUE DIRECTIONS CONCERNING THE INTERPRETATION OF NATURE. Francis Bacon. [Note on the Text] AUTHOR'S PREFACE.

Those who have taken upon them to lay down the law of nature as a thing already searched out and understood, whether they have spoken in simple assurance or professional affectation, have therein done philosophy and the sciences great injury. The idea of this study struck me six years ago after the first mention of the Black Irish as told to me in variant four of the myth.

The question of its origin, meaning, and purpose has haunted me ever since, primarily due to my own Irish heritage (my mother's family .

Extinction of the American Passenger Pigeon -- The True Story