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I I, I I t t' t II I, ~ ~ f I f I~ ~ l ~ ~I 08'!.tH.l3 SEellONFOUR least Tem Much of the information presented in this section was taken from the Biological Opinion prepared by the FWS for the Federal Energy Regulatory Commission's Preferred Alternative for the Kingsley Dam Project (Project No. 1417) and North Platte/Keystone Dam Project (Project No. 1835) (FWS 1997). 4.1 HISTORY The interior population of the least tern (Sterna antillarum) was listed as an endangered species on May 28, 1985 (50 FR 21792). The least tern is migratory and historically bred along the Mississippi, Red, and Rio Grande River systems and rivers of central Texas. The breeding range extended from Texas to Montana and from eastern Colorado and New Mexico to southern Indiana. From late April to August, they occur primarily on barren to sparsely vegetated riverine sandbars, sandbar islands, sand and gravel pits, and lake and reservoir shorelines. Today, least terns occupy scattered remnants of their former range where they nest on sparsely vegetated riverine sandbars, sand and gravel spoil piles, ash disposal sites of power plants, dike fields, and reservoir shorelines. All subspecies of the least tern apparently were abundant through the late 1880s, but were nearly extirpated as changing fashions popularized bird feathers and skins on hats. In the late 1800s, it was reported that as many as 1,200 adult least terns were killed in one day for their delicate plumage and as many as 100,000 were killed in one season. After signing of the 1918 Migratory Bird Treaty Act, which prohibited the sale, purchase, taking, or possession of any wild migratory bird, commercial harvesting became illegal and the species began to increase through the 1940s. However, human development and loss of riverine sandbar habitat subsequently lead to another rapid decline. By the mid-1970s, least tern populations had decreased by more than 80 percent from the 1940s (NGPC 1997). Recent population surveys have reported between 5,000 and 9,000 least terns scattered across the interior of the United States. 4.2 REASONS FOR DECLINE Channelization, water withdrawals (primarily for irrigation), and the construction of reservoirs and pools have contributed to the elimination of much of the least tern sandbar nesting habitat in the interior of the United States. Water development within the Platte River system has been extensive which has significantly reduced the annual instream flow volwnes in the Platte River basin (Williams 1978). Water depletions reduce the width and/or depth of water surrounding riverine nest sites that may increase predation and hwnan disturbance. Depletions also permit vegetation encroachment into nesting areas. Under extreme conditions, depletions can dewater river reaches sufficiently to create conditions in the river that will not support fish life. Conditions that can contribute to fish mortality include insufficient dissolved oxygen, elevated water temperatures, and/or stranding of fish. Although these factors can affect all life stages and sizes of fish, mortalities involving small fish can adversely affect the least tern since small fish are the principle food item of the least tern. The nwnerous dams and water diversion canals in the upper Platte River basin have reduced water and sediment discharge in the Platte River, resulting in the transformation of wide, open channels to multiple narrow channels separated by wooded islands (Eschner et al. 1983; IllS /II'eit1IN Wo..4oNanI t:I)de feI/fJR/ IllnIt:tJs SllF00972ll6OO/r1.doc 6t2I1999(9.S2 AM)/URSG'M:FS12 4-1