A mass release of 2,465 ring-necked pheasants (Phasianus colchicus) at a single site in previously unoccupied range in southeastern Iowa in the fall of 1970 was evaluated by studying mortality, dispersal, reproduction, and population levels. The spring cock population near the release site, sampled by crowing-count surveys, remained at the same level from 1971 to 1972. A 60% drop in the estimated hen population in the same area was accompanied by a drop in winter sex ratios from 4.1 hens/cock in 1971 (first winter after release) to 1.5 in 1972. These changes are thought due to the addition of young-of-the-year (71.2%), with an assumed sex ratio of 1:1. Twenty-three percent of the nests found in 1971 were successful. Roadside surveys and field observations in August show that 71.4% of the hens had broods in 1971, and that the average brood of age 6 weeks or older had 7.1 ± 1.1 chicks. A few birds dispersed as far as 21.5 miles immediately after release, but most stayed near the release site. Radially diverging crowing-count surveys revealed an area of concentration of birds within 2 miles of the release site in 1971; concentration expanded to 3 miles in 1972. Observed mortality during the 2 months after the release was not excessive. Weight changes of three groups of pheasants from the time of banding to the time of sampling show that birds collected from the field 1 month after release had gained more weight than birds held in captivity for the same time
