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'cJ'< C~ Table 4 ,--l ...-l Marsh and Water Bird Use-Days on ':J Monte Vista and Alamosa National wildlife Refuges (NWR) I:~:) Monte Vista NWR Alamosa NWR Species 1979 1980 1979 1980 Pied-billed grebe* 3,356 1,863 3,175 1,650 Whi te-faced ibis 3,550 2,050 4,720 3,150 American bittern* 3,190 3,600 2,520 3,950 Snowy egret* 650 520 9,250 2,100 Black-crowned night heron* 1,650 4,500 5,200 7,600 Virginia rail* 4,000 4,000 1,800 900 Great blue heron** 750 570 3,772 2,970 Greater sandhill crane** 388,150 509,100 40,800 53,100 Whooping crane** 217 406 65 119 Eared grebe 360 Western grebe** 20 160 80 White pelican 18 Horned grebe 1,350 120 Green heron 1,020 960 Sora rail 1,000 1,000 Common egret 10 Total 405,513 527,007 74,832 77 , 949 Use-days/acre 31.5 40.9 8.3 8.6 Use-days/acre average 36.2 8.4 * Breeders. ** Migratory birds of high Federal interest. During 1979-80, use by these three groups of species averaged 64.7 use-days/acre/ season at Monte Vista NWR. Aerial transects flown by Water and Power in 1978 indicated significantly higher concentrations of water birds using wetlands out- side Alamosa NWR (which had an average of 35.1 use-days/acre/season). Because the aerial transects were designed to reveal rough estimates of differential habitat use and not intended to produce population estimates, those transects cannot be used to estimate shorebird use-days for the Closed Basin project area. However, the transect data and knowledge of shorebird habitat preference suggest that Closed Basin project area supports higher use-days/acre/season of wetland than does Alamosa NWR. For the three groups of species we estimate 40 use-days per wetland acre per season or a total of 1.7 million use-days during the breeding season within the Closed Basin project area. 6