Have you ever observed a large number of swallows or grackles congregate and prepare for the “take-off”? Did you ever listen to the weird honking of geese as they journeyed southward through a cold, bleak, snow-laden sky? Where do you suppose they were going? Why?
Occasionally, one still hears the query, “Do birds migrate?” This is not so strange, for centuries ago Aristotle taught that certain species as the European Robin changed to another species as the Redstart with the approach of winter. Until the last century the hibernation theory was quite generally accepted. It was based upon the annual finding of many birds in the mud and marshes during migration. The poor creatures dropped from exhaustion or were unable to resume the flight after a short rest in the marsh, with the result that observers assumed they were preparing their winter dwelling in the weedy marsh to protect themselves from the cold of winter. Less than 50 years ago one author, in reviewing the literature on migration, found no less than 175 books and articles on the hibernation of swallows, which strange to say, is a migrant.
According to the Tartars, the larger birds transported the smaller ones; as for example, the Crane carried the Corncrake on its back. This, of course, was mere legend. The highly imaginative speculators of the 13th century maintained that the birds migrated to the moon. Hence, we readily realize that there was little scientific knowledge concerning the seasonal movements of the birds of the temperate and arctic regions.
Today, charts have been constructed indicating the important highways through the sky. Banding of the winged creatures has been the most important single factor in determining their pathways. However, the airplane and the camera have been extremely helpful.
Why do birds migrate? When the cold of winter approaches and the supply of food for most birds diminishes (since insects and worms disappear) the very existence of the feathered creature is jeopardized. Undoubtedly, you recall from a previous article on birds, that they surpass all other animals in appetite because their active nature necessitates such a great expenditure of energy and their temperature (110 degrees) requires the production of considerable more heat than most creatures. A constant consumption of food is required as they do not store it. In one instance a House Wren was recorded feeding its young 1217 times during a single day; a Scarlet Tanager devoured 630 gypsy moth caterpillars in 18 minutes; and a Maryland Yellow-throat ate plant lice at the rate of over 5,000 an hour. In fact the greatest value of birds lies in their ability to destroy insect enemies.
Also to be considered is the fact that the hours of daylight are greatly shortened with approaching winter, consequently their time of foraging is greatly reduced. Hence, birds instinctively seek another home during the inclement season.
Where do they migrate? Many have the mistaken notion that they simply journey to a warmer section as our own southern states of Central America where food is more plentiful and the temperature more favorable. However, the migratory maps indicate that birds of the Arctic as the Tern travel to the Antarctic-a distance of 11,000 miles-and those of the northern United States go to southern South America. Naturally they seek their own climate alternating between Arctic and Antarctic Zones and North and South Temperate Zones according to season.
Many species pursue different routes in autumn than they do in spring; for example, many follow the Atlantic Coast route in autumn and return by the Mississippi Valley. The impulse to migrate is so strong that birds will leave their brood behind them to starve when the urge seizes them.
Numerous experiments have been performed in an attempt to determine what directs a bird on its course. Although they found that the bird’s vision and sense of balance are unusually acute (in most cases) nevertheless, they are insufficient to direct them at night, through fog and over sea. In fact, they concluded, the arrival at the ultimate destination we can only attribute to a deep-seated sense of direction combined with a topographical memory developed in birds. Many attempts have been made to isolate the seat of this sense of direction. It cannot be truthfully said that to date any have been successful. None of the known senses seem to offer great possibilities. However, this does not explain the action of the young Golden Plovers who, while their parents follow the Atlantic Coastal route, make their first flight south by following the Mississippi Valley, arriving at the same destination. Certainly this cannot be ascribed to acquired deep-seated sense of direction and topographical memory.
Evolution minded naturalists, being unable to explain it scientifically, finally ended up in an attempt to interpret migration by the inheritance of acquired characteristics, that is, through the process of trial and error they have established definite routes for their spring and autumnal flights. These acquired experiences are transmitted en mass to the young.
We cannot agree with their interpretation for it is instinct which not only gives them the urge, but also guides them every foot of the way. Instinct is an irresistible, God-given directive force. It is instinct that directs the Tern for 11,000 miles to a similar climate in the Antarctic that it has left in the Arctic: it is instinct that guides the young Golden Plover for 3,000 miles unescorted by adults on its first flight to the winter quarters in the south.