Least terns nesting at sand- and gravel pits have low reproductive success because of predation and human disturbance. The availability of habitat and the reproductive success of least terns using the Missouri River depend entirely on the discharge of water from the mainstem dams. Untimely discharges for hydroelectric power and navigation continue to inundate interior least tern colonies. Least tern eggs and young are extremely vulnerable. When least tern colonies are disturbed, adults leave eggs or chicks unprotected, increasing their vulnerability to predators and severe weather.
Prolonged disturbances can lead to destruction or abandonment of the colony.
Predation by avian and mammalian predators, such as American crows, American kestrels, great horned owls, raccoons, coyotes, minks and feral dogs and cats, has been documented at nesting colonies. Studies along the Platte valley have shown that selenium and mercury concentrations were elevated above background levels, and selenium in particular might be affecting the reproductive success of least terns in the Platte valley study area. Agricultural chemical runoff into rivers and tributaries can affect the quality of least tern nesting and foraging habitat. More important, the effects of contaminants combined with the physical degradation of habitat and the increase in human disturbance could further accelerate population declines. Management and Outlook Nebraska supports one of the largest populations of least terns in the interior United States, and annual surveys to monitor least tern population status in Nebraska began in 1980.