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From September 1966 to September 1968, a study of the breeding behavior of mottled ducks (Anas fulvigula maculosa) was conducted at Rockefeller Refuge, Grand Chenier, Louisiana. Courtship and pairing began during August. Courtship displays resembled those described for the mallard (Anas platyrhynchos). Ninety per cent of the ducks were paired by February. Sex ratio during courting period was 1.5 males per female. Small ponds and water areas between wiregrass islands were used for courting. Cross-pairing between mallards and mottled ducks made up only 1 per cent of all pair observations. This low percentage of cross-pairing apparently occurred in part because mallards paired later than mostmottled ducks. Territorial behavior, beginning in late February and early March, tended to space nesting birds. Home range size of four ducks was determined by radiotelemetry, and ranged from 105 to 327 acres. Home ranges may have been underestimated because of short transmitter life and optimal water conditions in the study area. Carrying capacity of homogeneous wiregrass habitat may be increased by level ditching or by pothole blasting.