Survival of juvenile ring-necked ducks on wetlands of different pH

Brood and duckling survival of ring-necked ducks (Aythya collaris) was examined in relation to wetland water chemistry in eastcentral Maine during 1983-85. Daily survival rates (DSR) of broods and ducklings were determined for 381 ducklings from 64 broods by counts of each brood at 6-10-day intervals during broodrearing. Twelve of 64 females lost entire broods. Only 176 of 381 (46%) ducklings survived to fledge. Brood survival for the 45-day rearing period was 0.7731; duckling survival was 0.3707. Young ducklings ( 6.1) wetlands (0.9816/day) (P = 0.049). Class IIb-III (25-45 days old) ducklings from the lowest-pH wetlands ( 6.5) had the highest DSR (0.9856) (P = 0.009). J. WILDL. MANAGE. 52(2): 169-176 Ring-necked ducks have fairly high annual harvest rates, though populations on wintering areas may be declining (Conroy and Eberhardt 1983; U.S. Fish and Wildl. Serv., Off. Migr. Bird Manage., unpubl. data). Conroy and Eberhardt (1983) reported that age ratios for ring-necked ducks harvested in fall in the Atlantic Flyway (1961-81) were lower than those from the Mississippi Flyway (1.18 vs. 1.29 young/ad). The northeast receives acidic precipitation (Cowling 1982); almost 17% of the 3,100,000 km2 of breeding area of the ring-necked duck is vulnerable to acidification and up to 34,000 pairs could be affected (Longcore et al. 1987). Wetland acidification could adversely affect waterfowl by lowering diversity or biomass of invertebrates in wetlands used by breeding adults or ducklings. Female ducks rely on protein-rich invertebrates for egg laying, and ducklings require ample protein and nutrients for growth (Swanson and Meyer 1973, Krapu 1974, Reinecke 1979). Reductions in invertebrates during broodrearing may lower survival of ducklings and reduce recruitment. Brood surveys are used to estimate production and apparent survival rates (ASR) of ducklings. However, estimates from this method overestimate production because there is no accounting for loss of entire broods (Ball et al. 1975, Reed 1975, Ringelman and Longcore 1982, Talent et al. 1983). We estimated survival rates of ring-necked duck broods and ducklings in eastcentral Maine by relocating broods at regular intervals and recording duckling attrition over time. We estimated survival rates of older and younger ducklings and related differences in survival to differences in pH and alkalinity of the broodrearing wetland. We thank A. G. LaRochelle, P. E. Malicky, C. J. Reid, D. D. Eggeman, R. R. Roy, J. R. Kelly, R. D. Stratton, J. C. Lewis, J. D. Stanton III, J. P. Gibbs, T. P. Hodgeman, and J. A. Barker for assistance with brood surveys and sorting invertebrates. T. M. Mingo and C. J. Reid identified invertebrates. K. L. Stromborg analyzed water samples. J. D. Nichols gave helpful advice during the planning stages and on analyses of survival rates. C. M. Bunck, G. W. Pendleton, P. H. Geissler, and L. M. Moyer helped with statistical analyses of invertebrate data. J. E. Hines and R. E. Munro gave programming support. Helpful comments on early drafts of this manuscript were made by J. D. Nichols, G. M. Haramis, M. A. Howe, D. H. White, M. J. Conroy, and an anonymous referee. STUDY AREA AND METHODS About 17% (15,000 km2) of the land area of Maine has "low to no acid-neutralizing capacity [ANC]" (i.e., sensitivity Class 1 [Norton 1980: 524]). Our study areas were selected to represent Class 1 and Class 2 (low-moderate ANC) terrain and consisted mostly of wetlands in Hancock and Washington counties in eastcentral Maine. The 66-km2 Cherryfield study area was located