Forest Preserve District of Cook County, Illinois
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Migration of Insects, Fish and Mammals
Nature Bulletin No. 148   March 27, 1948
Forest Preserve District of Cook County
William N. Erickson, President
Roberts Mann, Supt. of Conservation


Birds are not the orly animals that migrate. A sense of direction, or "homing instinct", seems to be highly developed in certain insects, fish and mammals. Bulletin No. 147 mentioned the migrations of bats. The fur seals of the eastern Pacific Ocean all congregate upon the Pribilof Islands in the Bering Sea to bear and raise their young. Mountain- dwelling deer, elk, bighorn sheep and goats migrate to lower levels each autumn. Buffalo used to migrate in vast herds.

Some butterflies and moths migrate. In early fall the Monarch Butterflies congregate in groups and, later, flocks of many thousands mya be seen flying southward. In spring, often battered and bedraggled, they return. Bees do not migrate but their homing instinct is so remarkable that the shortest distance between two points is commonly called a "bee line". They apparently memorize landmarks and return home by sight. Bees taken several miles inland from their hive on the shore of the lake, returned home safely; but when the same bees were released from a boat several miles out in the lake, none of them returned.

Herring, mackerel and other fish migrate in huge numbers to shallow waters where their spawn can find food and protection from enemies. And a later bulletin will tell of the curious migration of the eels from all the rivers tributary to the Atlantic Ocean, to one deep spot where they lay their eggs and die; and how the young eels return to the same streams from which their parents came.

The Pacific salmon do just the opposite. These large fish lay their eggs and then die in the headwaters of the streams of Oregon, Washington, western Canada and Alaska. The eggs hatch and the young fish live there two years before they go downstream and out to sea. There they gorge themselves and grow rapidly for two more years. Then each fish returns to the mouth of the river from which it came and fights its way back upstream, jumping up over water falls and dams, until it reaches the same tributary where it was hatched. There they mate, lay their eggs, and die.

Nothing but a poor fish would go to all that trouble.

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