How do they know that it is time for them to go into your long flight? It is known that they fly every year at the same time, when there is a change of seasons. What is the true, infallible sign of this change? Of course, not temperature. We all know that autumn and spring may be late or early. The most clear and unmistakable characteristic is the duration of the day. Birds are able to determine when the days become shorter (or longer - in the spring), and it serves as a signal for the beginning of the flight. Although the temperature change and the amount of food may also provide an additional pulse to the beginning of the flight.
It was considered that as the seasonal flights and the return of birds to the old nesting place for the main role is played by instincts. Support for this view a lot. So, Professor Maiwald from California many years watched ringed bird - the bald zonotrichia that annual return in your garden, on your hive at the house of Professor, flying three and a half thousand kilometers from Alaska, where of zonotrichia build their nests.
In 1941, the ornithologist With. Tours watched even more touching commitment suburban starlings and skylarks to their native land. In spring, they, as usual, came from the South and found the water surface of the Rybinsk store, which a year ago was not. Arrived starlings took their old birdhouses, although they looked now from the water and fly from them for food for future children was very far away. And larks for a long time carried their trills over spilled water because it was their own field! It is the instinct attributed to the fact that in the spring the birds are coming back not only in the same country, but often even in the same nest in the same house!