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I' -, ., I I t I II l II J I , I t I ~ I C0:.!)~4 SECTIONFOUR least Tern \ colonies in denser vegetation may be a response to habitat loss or a function of strong site tenacity. Eventually, least terns will abandon heavily vegetated nesting sites. Least terns are colonial nesters, meaning they nest in close proximity to each other, and they benefit from the anti-predator behavior exhibited by the entire colony when the nesting territory is invaded. If a predator or some other disturbance disrupts the colony, adult least terns dive- bomb, defecate on, and shriek at intruders in a mobbing fashion to persuade the invader to leave. During the breeding season, the tern's home range is generally limited to 2 miles from the nesting location. Least terns nesting at sand pits along rivers use the adjoining river as well as the sand pit lake for foraging. Upon arrival at the breeding grounds, least terns begin to engage in courtship displays. Soon after pair formation, both sexes participate in making many shallow nest scrapes dispersed in open, gravelly, or sandy areas. Although a pair may build several scrapes, only one is used for nesting. Nest scrapes are sometimes located near small pieces of wood or debris or near clusters of small stones which may make the nest less noticeable to predators. After the female selects a suitable scrape, two or three eggs are laid. The eggs are pale to olive-buff and are speckled with streaks or splotches of dark purplish-brown, chocolate, or blue-gray. If a first clutch of eggs is lost, they will renest up to two times at a new location. . Incubation, which is shared by both adults, begins after the first egg is laid and lasts for about 21 days. All chicks usually hatch within 24 hours (Kirsch 1990). Chicks are precocial and are brooded for approximately 6 days after hatching (Wilson 1991). A day or two after hatching, the chicks begin to wander from the nest scrape and become increasingly mobile. Both adults catch small fish, which are fed to the chicks. The chicks fledge approximately 21 days after hatching, but they do not become competent at fishing until after migrating from the breeding grounds in the fall (Whitman 1988; Wilson 1991). Least terns are generally a long lived species and banding results have shown that natural longevity can exceed 20 years (NGPC 1997). The least tern is piscivorous (fish eater) and forages in shallow waters of rivers, streams, reservoirs, and ponds and feed almost exclusively upon small schooling fish (Atwood and Kelly 1984; Wilson et al. 1993). In Nebraska, important forage fish genera include: Fundulus, Notropis, Campostoma, Pimephales, Cyprinella, Dorosoma, Lepomis, and Carpiodes. Least terns are viewed as opportunistic feeders, exploiting any fish within the 1- to 3-inch size range. Riverine habitat along the Platte River continues to be important to the life requirements of the least tern, despite the presence of forage fish in the sand pit lakes. Successful nesting at sand pits does recruit birds into the population. However, birds nesting at these non-riverine locations move to the river upon chick fledgiilg and continue to use this riverine habitat until their southward migration. The presence of a healthy forage fish community in the Platte River is imperative to the success ofleast tern nesting efforts along this river. Baseline information regarding forage fish in the central Platte River is provided in Section 9.2 of this report. Following the breeding season, least terns gather in small flocks along rivers to feed and prepare for migration. .1n Nebraska, fall migration usually takes place from mid- or late July to early September (NGPC 1997). Little is known regarding the wintering area(s) of interior least terns (FWS 1990). Least terns of unknown populations or subspecies are known to OCCIlI during the _ Breiner IMIiIIdwant "'* Ff1I/eIaISetrtt:es . saF0D972a6OO1n."", 6/2I'909{~52AM)lURSGWCFS12 4-3