Forest Preserve District of Cook County, Illinois
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Fish-Eating Birds
Nature Bulletin No. 307-A   May 18, 1968
Forest Preserve District of Cook County
Richard B. Ogilvie, President
Roland F. Eisenbeis, Supt. of Conservation

FISH-EATING BIRDS
Man adopted checks and balances as a part of government long after they were part of nature. Since prehistoric times, these complex relationships between the hunters and their prey -- between the eaters and those eaten -- have gradually developed to check the overabundance of any species. Their absence is unnatural. Nature, let alone, is always orderly, Man, however, is radically changing the face of the earth by draining and levying submarginal lands, ploughing the prairies, clear-cutting the forests, and polluting the streams. In his zeal to "manage" and "improve" wildlife populations, he has upset many of those relationships and destroyed many of the natural checks and balances.

Fish, for instance, lay enormous numbers of eggs -- thousands or hundreds of thousands. Not all of these hatch and, of those that do, only a few reach maturity. This is good: there cannot possibly be room or food for all of them. We see this most strikingly in inland lakes and ponds. A body of water contains just so much oxygen, food and space. If the fish in that water are to benefit from these essentials, reach maturity and keep on growing there must be no more than a limited number of them. There are only two drumsticks on a turkey.

Injury, disease and other natural causes -- remove many eggs and young fry but not enough. Other fish eat them and bigger fish may eat those fish. Snapping turtles, water snakes, mammals and, especially, fish- eating birds help remove the surplus and keep the fish population on an even keel. Without sufficient numbers of fish-eating birds and other predators, the fish in a body of water become overcrowded, stunted, thin, and not worth the taking. Sportsmen who complain of poor fishing in so many of our inland waters, and wonder why it is not as wonderful as it was when the white man first came, forget that in those days there were great numbers of fish-eating birds -- herons, egrets, bitterns, loons, mergansers and several other species of diving ducks, cormorants, grebes, terns, ospreys, bald eagles, kingfishers, gulls, crows and pelicans.

In the Chicago region, even though we have restored or created many lakes, ponds and marshes in our forest preserves, many of these big birds are uncommon or present only during part of the year. Occasionally we see a stray pelican. A few loons spend some time here on their way to and from the lonely lakes in Canada and also, in spring and fall, a few ospreys and some bald eagles. Cormorants, mergansers, large numbers of bluebills or scaups, and some of the other diving fish- eating ducks rest and feed here during their migrations. Bitterns and three kinds of herons -- the great blue, the little green, and the black- crowned night herons -- are fairly common. In recent years, increasing numbers of American egrets have come up the Mississippi and Illinois valleys in midsummer after their nesting season in the south. Some snowy egrets and little blue herons are beginning to accompany them on these "reverse migrations".

Gulls and crows are scavengers and very numerous at all times. They frequent our garbage dumps. They clean up all the dead fish in our waters, but even the gulls seldom catch a live fish unless it is a cripple or unless a school of small ones is found swimming near the surface. Kingfishers, however, constantly patrol our streams and lakes: swooping down to seize small fish and pursuing them underwater. We need more kingfishers.

These birds are stream bankers that keep checks and balances.


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