Reproductive Success Intraspecific Nest Parasitism And Nest Site Fidelity Of A Pacific Flyway Population Of The Wood Duck Aix Sponsa

Examines how nest box placement affected wood duck nesting success, as well as relationships between physiological factors and box choice.

Abstract: Wood duck breeding biology has largely been studied in artificial nest boxes, but environmental influences on nesting biology must be studied in the context within which wood ducks evolved (i.e. natural tree cavities). Previous work suggested that intra- and inter-seasonal changes in abundance of invertebrate foods and/or accessibility of tree cavities may affect nesting season length and the breeding chronology of wood duck hens. This study examined the relationships of intra-seasonal and annual variation in invertebrate food abundance and leaf emergence with nesting chronology, nesting effort, and nest parasitism rates in a southern Illinois' wood duck population that nests in natural cavities. Nest chronology, nesting effort, and parasitism rates were studied during 1994 -- 1998 and 2001 -- 2002. I modeled wetland conditions with local precipitation and stage of the Mississippi River. Wetland invertebrate food abundance was measured by sweep- net sampling in seasonal and semi-permanent wetlands in 2001 and 2002. Invertebrate sampling was completed during four nesting periods (egg laying, late egg laying/early incubation, incubation! early hatch, hatch) during 2001 -- 2002. Weekly leaf emergence in 2001 and 2002 was measured with a Model-A Spherical Densiometer, from the onset of leaf emergence through the period of maximum upper story leaf coverage. Annual nesting effort of radiomarked hens known to incubate clutches ranged from 42% - 70% throughout the study. Clutch sizes >14 (indicative of nest parasitism) ranged from 8% - 43% during the study and varied inversely with nesting effort. High nesting effort was observed in years with the most stable water levels during egg laying and incubation. Invertebrate biomass did not differ throughout the 2001 (P = 0.76) and 2002 (P = 0.17) nesting seasons. During hatch, densities in 2002 were 1.7 times higher than egg laying and incubation/early hatch; however did not differ from late egg laying/early incubation (P = 0.05). Mean invertebrate densities were not significantly different (P = 0.87) during 2001. Two commonly consumed invertebrates known to occur during nest initiation and hatch, Isopoda and Diptera (primarily Chironomidae), were 10.2% and 18.4% more numerous during the egg laying and hatch (P