Survival and habitat use of Mallard (Anas platyrhynchos) broods in the San Joaquin Valley, California

The Central Valley of California is an important breeding area for Mallards (Anas platyrhynchos), but estimating recruitment rates for this population has been hampered by lack of data on duckling survival. To gain a better understanding of factors affecting brood and duckling survival, we radiomarked 56 brood hens and 112 ducklings (two per brood) on two actively managed wetland complexes in the San Joaquin Valley during 1996-1997. Total brood mortality was extensive, affecting 27 of 53 broods (51%). Survival of individual ducklings from hatching until 30 days of age was 24.8% (95% confidence interval: 0.178-0.335), with most mortality resulting from predation during the first 12 days of life. Survival differed between years and study areas but was unaffected by hatching date. Broods preferred reverse-cycle seasonal wetlands to more permanent wetlands throughout their first 30 days of life, and ducklings also had higher 2- to 30-day survival probabilities in reverse-cycle wetlands (x̄ ± SE = 0.755 ± 0.095) than in semipermanent-permanent wetlands (0.189 ± 0.056) or moist-soil units (0.173 ± 0.067). We recommend that waterfowl managers in the Central Valley provide reverse-cycle seasonal wetlands during the brood-rearing period to enhance survival of locally breeding Mallards.