Question

1. Many migratory birds may be guided by the ....during the day and ....at night. There is some evidence that birds may use the ...of the earth to find....​

Answer 1

Answer:

Migrants often return to breed in the exact locality where they were hatched or born. This journey homeward, particularly that of birds, may cover thousands of miles.





Homing experiments have demonstrated the ability of animals to orient themselves geographically. Such experiments involve removing animals from a specific point (usually the nest), transporting them for various distances, and analyzing their speed and degree of success in returning. Starlings have returned to their nests after being transported 800 kilometres (500 miles); swallows have returned a distance of more than 1,800 kilometres (1,100 miles). A Manx shearwater (Puffinus puffinus) returned from Massachusetts to Britain, 4,900 kilometres (3,050 miles) across the Atlantic, in 12 1/2 days. Laysan albatrosses (Diomedea immutabilis) returned to Midway Island in the Pacific after being released at Whidbey Island, Washington; the journey covered 5,100 kilometres (3,200 miles) and took 10.1 days. Experiments with certain fishes and mammals have demonstrated similar homing ability.

It is apparent that homing animals use familiar landmarks; both random and oriented searches have been observed in birds and fish. Homing experiments with gannets observed from aircraft have demonstrated that, after release, the birds explore the region and hesitate as they apparently look for landmarks. Landmarks vary from topographical (for example, mountain systems, river systems, and coastlines) to ecological (such as vegetation zones) to climatic (e.g., air masses differing in temperature and humidity, prevailing winds). Fishes may orient themselves by using similar clues in the same way. Passive drifting is an important factor in the movements of larvae and young fishes, such as those of the eel, cod, herring, and plaice, and even in adult fishes that are passive after spawning, such as herring and cod. As a result of drifting with the current, the movements of such fishes are similar from year to year.

Familiar landmarks and exploration do not, however, explain how migrants find their way along routes covering many hundreds or thousands of miles nor do the results of most homing experiments.