Great Migrations Reading Passage
Great Migrations Reading Passage
Paragraph A
Animal migration is far more than just the movement of animals. It can be vaguely described as a movement that occurs at regular intervals, mostly annually, involving many species of animals and is rewarded only at the end of the long journey. It shows inherited instinct. Hugh Dingle, a biologist, recognised five features that apply, in varying combinations and degrees, to all migrations. They are prolonged movements that bring animals outside their familiar habitats. The route is linear, not zigzaggy. It involves special behaviours like preparation, such as overfeeding and arrival. Animals need to specially allocate energy for the migration. They maintain an intense focus on the greater mission, which keeps them undistracted by temptations and undeterred by challenges that would turn other animals aside.
Paragraph B
On its 20,000 km flight from the extreme south of South America to the Arctic Circle, an arctic tern will take no notice of a fish that a bird-watcher gives along the way. The tern flies on while local gulls will dive voraciously for such handouts. Why? By an instinctive sense, the Arctic tern resists distraction because it is driven by a larger purpose at that moment—something we humans admire. It is persistent in reaching its destination. The bird understands that it can eat, rest, or mate later on. During the process, it is completely focused on the journey; its goal is the destination.
Paragraph C
The larger purpose will be served by reaching some coastline in the Arctic, upon which other arctic terns have gathered. It will find a place, a time, and an environment in which it can lay eggs and rear offspring.
Paragraph D
Migration is a complex problem, and biologists view it differently, depending on what type of animals they study. Joel Berger from the University of Montana, researching the American pronghorn and some large terrestrial mammals, prefers what he calls a simple, practical definition suited to his beasts: "movements to a home area from another area and back again." Mostly, the reason for such seasonal migration is to seek resources that aren't available within a single area throughout the year.
Paragraph E
Vertical movements by zooplankton daily in the ocean—upward movement to seek food at night and downward movement to escape predators during the day—can also be considered migration. Also, the movement of aphids after depleting the young leaves on a food plant, their offspring then fly towards a different host plant, and no aphid ever returns to where it started.
Paragraph F
Dingle is an evolutionary biologist who researches insects. His interpretation is more complicated than Berger's, citing those five features that differentiate migration from other forms of movement. They allow for the fact that aphids will become sensitive to blue light from the sky when it's time for takeoff on their big journey and sensitive to yellow light when it is time to land.
Paragraph G
Birds will feed heavily in advance of a long migrational flight to fatten themselves. Dingle argues the value of his definition is that it focuses attention on what the phenomenon of wildebeest migration has in common with the phenomenon of the aphids, and therefore helps guide researchers towards understanding how evolution has created them. However, human behaviour is having a detrimental impact on animal migration.
Paragraph H
The pronghorn resembles an antelope even though they aren't related, and it is the fastest land mammal in the New World. One population follows a narrow route from its summer range in the mountains, across a river, and down onto the plains, spending the summer in the mountainous Grand Teton National Park of the western USA. They wait out the frozen months here, mainly feeding on sagebrush clear of snow. These pronghorns are notable for the severity of the constriction and invariance of their migration route at three bottlenecks. They can't reach their bounty of summer grazing if they can't pass through each of the three during their spring migration. They will likely die trying to overwinter in the deep snow if they don’t pass through again in autumn, escaping south onto those windblown plains.
Paragraph I
Pronghorn traverse high, open shoulders of land where they can see and run. They are dependent on speed and distance vision to be safe from attacks. Forested hills rise to form a V at one of the bottlenecks, leaving a corridor of open ground only about 150m wide, filled with private homes. Increasing development creates a crisis for the pronghorn, threatening to block off their passageway.
Paragraph J
Biologists, along with some conservation scientists and land managers within the USA's National Park Service and other agencies, are now working to conserve migrational behaviours, not just species and habitats. A National Forest has identified the path of the pronghorn, much of which passes across its land, as a preserved migration path. Neither the Forest Service nor the Park Service can control what happens on private land at a bottleneck. And with some other migrating species, the challenge is further complicated by vastly greater distances traversed, more jurisdictions, more borders, and more dangers along the way. We will need knowledge and determination to ensure that migrating species can continue their journey longer.
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