WSP00190

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 6/2/1999
• Author: URS Greiner Woodward
• Title: Documentation of Existing Conditions in the Central Platte Valley - Delivery Order Number 86
• Water Supply Pro - Doc Type: Report/Study

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SECTIONFOUR

Least Tern

gravel component ranged from 0.5 to 92 acres and averaged 18.3 acres, and the surface area of
water ranged from I to 150 acres and averaged 27.4 acres (FWS 1997).

The number of active mining operations, as well as the total size, areas of sand and gravel, and
surface areas of water at each site did not remain constant during 1988 to 1991. New sand pit
lakes were created (n=7), spoil piles became vegetated (n=4) or developed with housing (n=I),
and features of active sites changed as mining progressed. However, size of the operation,
amount of exposed sand and gravel, and surface area of water were strongly correlated. In a later
study, Kirsch (1996) found that sand pit sites used by least terns along the lower Platte River had
greater areas of water and were larger than unused sand pit sites (FWS 1997).

Site Fidelity and Movement

Research on the central Platte River has revealed important information on nest site fidelity,
movements, and reproductive success (Lingle 1993).

Site fidelity. Distances of nesting birds from their banding origin extended from 0 to 170 miles
(based on 163 sightings of 109 individuals). Five percent of the least terns resighted were
banded as chicks and 28 percent of the least terns returned to the colony where they were banded
(FWS 1997).

Immi2T3tionlEmi2J"Stion. Eleven sightings often banded least terns confirmed population
mixing between Kansas and Nebraska and within the Platte River valley itself. An adult least
tern banded in 1984 on a nest at Quivira National Wildlife Refuge (NWR) in Kansas, was
captured on a nest near Kearney, Nebraska in 1987, 170 miles north of where it was banded. A
least tern chick banded at this same site in 1987 was recovered at a nest at Quivira NWR in 1990.
Three chicks banded on the lower Platte River were later recaptured on nests in the central Platte
River, up to 125 miles from their natal colony. Conversely, one adult banded near Kearney,
Nebraska in 1988 was found nesting on the lower Platte River near Fremont, Nebraska in May
1989, 150 miles downstream from where it was banded. After successfully hatching its eggs, it
was observed near Grand Island, Nebraska in July 1989 (FWS 1997).

Local MovementslPost-nestinl: Dispersal. Sightings of color-banded least terns (n=54)
revealed movement and dispersal patterns. In about 80 percent of the observations, birds moved
from sand pit sites to riverine sites. Least terns rely heavily on the river for foraging and loafing;
generally foraging within one mile of their nest sites. Foraging movements from nests at sand
pits to the river were readily observed at several sites and ranged from 0.25 to 1.5 miles. Post-
fledging chick movements were generally to the river from sand and gravel sites. The exception
was when high flows forced the birds off the river to the spoil piles, as was documented on two
occasions. Once the chicks attained flight, they would accompany their parents to the river. In
1990, one least tern brood that was less than 7 days old moved to the river from an adjacent sand
pit before fledging (FWS 1997).

The Platte River provides vital nesting, loafing, and foraging habitat for least terns and serves as
a post-nestinglpre-migrational congregation or staging area. Congregation areas were noted, and
all but one were also nesting sites. These sites were used up to 30 days. The U.S. Highway 34
bridge southeast of Grand Island, Nebraska served as a congregation site from July 12 to August

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