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Nests were found using hand drags on the islands and with a cable-chain device towed between two vehicles (Higgens et. al. 1969) in the other habitats. At least 3 searches were completed during the nesting period at an interval of approximately 21 days. Over the 12 years these searches have been operated, a total of 548 nests were found on a cumulative total of 2,336 acres of habitat. On 276 cumulative acres of island habitat, 191 nests were discovered (69.2 nests per 100 acres). This may be compared with 297 nests discovered on 1,670 acres of wet prairie-meadow (17.7 nests per 100 acres) and 60 nests on 390 cumulative acres of dense nesting cover (15.4 nests per 100 acres).

Both Mallards (Anas platyrhynchos) and Northern Pintail (A. acuta) favored the artificial islands for nesting with better than 50 percent of the nests of these species found on this habitat. Blue-winged Teal (A. discors), Northern Shoveler (A. clypeata) and Gadwall (A. strepera) nests were most frequently found in the wet prairie-meadow.

Nest success was calculated by the Mayfield 40 percent method (Johnson, 1979) and ranged between 15 percent for native prairie-meadow to 25 percent on the island habitats. Overall success for all habitats at Delta was 18 percent.

Almost four times as many nests with a substantial increase in success can be attributed to the construction of islands in the Delta area. More than half of the nests discovered on the islands were Mallards and Pintails.