However, much of the best breeding habitat has been lost or disturbed due to river damming, dredging, and straightening. By regulating the rivers, we have disrupted the flood cycle that scoured vegetation out of the riverbed and shifted sandbars in the wide river bottom. Regular flooding reduces the invasion of the riverbed by plants. However, floods during the breeding season can wash away tern nests, eggs, and chicks. Too little water in the river also can adversely affect the tern population. Not enough water in the river can result in fewer fish and consequently reduce the food source for terns. To be successful along Oklahoma’s rivers, breeding terns need a combination of suitable sandbars, favorable water levels, and sufficient food during the nesting season.
In addition to changes in natural river processes, terns also are threatened by increased disturbance by humans. Our rivers have become popular recreation areas, and the number of people on the river is increasing. ATV use in and along rivers has grown, hurting ground-nesting birds. Because terns build well-camouflaged nests on the bare sand, their simple nests are vulnerable to trampling by people, pets, and livestock. Even if we do not destroy the nest, human activity can keep parent birds away from the eggs and chicks, leaving them subject to overheating in the summer sun or predation by animals such as coyotes, crows, or raccoons.