There is a growing interest in the use of pen-reared wood ducks (Aix sponsa) for establishing or increasing box-nesting populations in local areas. During a 3-year period (1967-1969), 67 pen-reared hens were released on the Patuxent Wildlife Research Center, Laurel, Maryland. These releases substantially increased the nesting population. Total population averaged less than 30 hens annually with a recruitment rate averaging less than seven between 1963 and 1967. Between 1968 and 1971, the nesting population averaged about 80 hens. Annual recruitment averaged 29 between 1969 and 1971. Pen-reared hens were as successful as wild hens in hatching and rearing young. Mortality was lower among pen-reared hens than wild hens, due largely to the sedentary behavior of the pen-reared hens. Production of young to flight stage increased from an average of about 100 per year prior to the releases of pen-reared hens to about 430 annually after the last release in 1969. Pen-reared wood ducks (Aix sponsa) have been released in a number of areas in the past 25 years in attempts to establish populations where the birds were absent, or to augment populations below the carrying capacity of the habitat (McCabe, 1947; Hanson, 1951; Grayson and Grayson, and 1959; Hunt and Smith, 1966). In a comprehensive review of these experiments, Lee and Nelson (1966) concluded that the data, though inadequate from these many small-scale releases, were encouraging enough to suggest the desirability of more in-depth studies. Recent interest in this technique has been particularly evident in the Southeast where the Division of Refuges, Bureau of Sport Fisheries and Wildlife, released pen-reared wood ducks on several refuges (Lane, Bond, and Julian, 1968). These releases have resulted in establishment or increased populations on at least five national wildlife refuges. Several studies of wood duck ecology have been conducted on the Patuxent Wildlife Research Center near Laurel, Maryland, since 1963 (McGilvrey, 1969; and McGilvrey and Uhler, 1971). Although the habitat was excellent and brood rearing success good, nesting populations declined from 1963 through 1966 as recruitment of young hens failed to exceed losses of older birds. I released 67 pen-reared hens and 72 pen-reared drakes prior to the nesting season in 1967, 1968, and 1969. This paper discusses the impact of these releases on the nesting populations in subsequent years through 1971.
