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The migration of birds

Migration is the perilous seasonal journey undertaken by many bird species. In the northern hemisphere it is prompted by the scarcity|scarceness(SCARCE) of food. Migrants are also genetically(GENE) programmed to respond to the changing length of the day as autumn approaches. Nevertheless, in the tropics, where there is little variation in the amount of daylight, migration is still a surprisingly common occurrence(OCCUR)

Many birds will display considerable restlessness before beginning their journeys. Their sensitivity(SENSE) to the earth’s magnetic field helps them navigate, but inexperienced birds may get things spectacularly(SPECTACLE) wrong and end up far from their intended destination.

In the past, the return dates could be predicted with great precision but climate change makes this harder. Although it is advantageous(ADVANTAGE) for birds to return earlier than their rivals so they can establish territories, getting back too early could have incalculable consequences for their long-term survival. However, some birds are progressively(PROGRESS) reducing the distances they migrate in response to a milder climate. Their adaptability in such a short period in evolutionary(EVOLVE) terms has greatly surprised scientists.

Test 2 / 30


The twentieth century witnessed a momentous(MOMENT) change in the relationship between science and society. In World War I scientists were conscripted and died in the trenches. In World War II they were exempted as national treasures and committed to secrecy(SECRET), and they rallied behind their country’s war effort. The explanation of the change is not hard to find – governments came to believe that theoretical(THEORY) research can produce practical improvements in industry, agriculture, and medicine.

The belief was firmly reinforced(FORCE) by developments such as the discovery of antibiotics and the application(APPLY) of nuclear physics to the production of atomic weapons. Science became so identified with practical benefits that the dependence of technology on science is commonly(COMMON) assumed to be a timeless(TIME) relationship and a single enterprise. Science and technology, research and development these are assumed to be almost inseparable(SEPARATE) twins. These rank among the sacred phrases of our time. The belief in the coupling of science and technology is now petrified in the dictionary definition of technology as applied science.