Overpopulation is not just a problem for mankind - it can be a problem for ''birdkind'' as well. Consider the case of the terns vs. the sea gulls on Petit Manan and Green Island off the Maine coast.
Wildlife managers with the United States Fish and Wildlife Service are claiming success this summer in eliminating what had become a teeming nesting area for ever-proliferating sea gulls on the two islands. It is a move that officials say has already helped bolster the region's dwindling tern population.
In recent years, larger, more aggressive herring gulls and great black-backed gulls had moved into and taken over what seven years ago was the largest tern-nesting area on the Maine coast. The gulls were able to move in because they traditionally nest earlier than the terns, beating them to the prime nesting spots by two or three weeks. In addition, the large gulls are known to prey on tern eggs and chicks.
As a result, between 1977 and 1982 the nesting population of terns on the two islands had dropped by 40 percent.
The proliferation of gulls was in part due to the availability of a steady, reliable source of food - primarily garbage in urban landfill areas. Terns, on the other hand, feed on small, live fish. They are thus more subject to natural population fluctuations, biologists say.
Federal officials decided that the most efficient way to open the island for tern nesting and prevent the gulls from returning would be to poison the gulls.
Small cubes of bread laced with gull poison were spread throughout the gull nesting area. Some 668 gulls were killed. The actions raised objections from some Maine residents who were concerned about the use of toxins and the killing of the sea gulls. Federal officials say the action was necessary to give a much needed boost to the tern population.
''We hope people will understand that this is sometimes necessary for the sake of another species,'' says Inez Connor of the Fish and Wildlife Service.
Ms. Connor adds that the action has permitted nearly 25 percent of the region's tern population to return to nest on the islands. It was done, she says , at the expense of only a small percentage of the sea gull population.
There are an estimated 30,000 nesting pairs of common terns in the Northeast, as well as an estimated 3,000 pairs of the more rare roseate terns. By contrast there are an estimated 180,000 nesting pairs of sea gulls.
Federal officials had expected that it would take several years before large numbers of terns began coming back to nest at the two islands. But they were pleased to find that the terns began coming back almost immediately.
''Much to our surprise they came back much more rapidly than we thought they were going to,'' says Paul O'Neill, a refuge staff assistant with the Fish and Wildlife Service.
At last count on the two islands, there were 450 nesting pairs of arctic terns; 650 pairs of common terns; and 15 to 20 pairs of roseate terns, including some razorbills, murres, and 12 individual puffins.
Connor says there were also 200 pairs of laughing gulls, a smaller species of gull that is not prone to harass nesting terns.
There are still some 400 individual herring gulls and 300 great black-back gulls on the islands. But federal officials say that these pose little threat to the nesting terns and will be permitted to remain in the area. ''These gulls are loafing rather than nesting, and that cuts down on their predation,'' Connor says. ''At this point they are just using the island and the area to loaf, and rest, and so forth.''
The tern restoration project was jointly run by the Maine Audubon Society, the State of Maine, the College of the Atlantic, and the Fish and Wildlife Service.