Cavity availability and use in hardwood forests with emphasis on wood ducks

Abstract

The availability and use of cavities were examined on Tony Houseman State Park and Wildlife Management Area at Blue Elbow Swamp (HWMA), Orange County, Texas, during 1999. Random 0.25-ha plots were used to inventory cavities by size and estimate cavity use by vertebrates. Tree species, number of cavities by entrance size, stems per ha, basal area, and total cavities were recorded in 23, 15, and 15 plots in the cypress-tupelo (Taxodium distichum-Nyssa aquatica), mixed hardwood, and pine-oak (Pinus spp.-Quercus spp.) forest stands, respectively. Cavities with entrance dimensions suitable for entry by wood ducks (Aix sponsa) were inspected for suitability as wood duck nesting sites. Total cavity densities were similar between forest stands, but cypress-tupelo contained significantly (P = 0.000) more large-size cavities and mixed hardwoods produced the greatest density of small cavities. Tree species important for cavity production varied by forest stand. Regardless of species or stand, larger diameter and dead trees provided cavities in greater proportions than their availability in forest stands. Suitable wood duck nesting cavities were found at densities (0.0-26.7 cavities/100 ha) comparable to other forest stands at similar latitudes. Wood ducks were captured using grain-baited, swim-in traps. Backpack (n = 13) and implant (n = 20) radio-transmitters were attached to wood duck hens in 1999 and 2000, respectively. A combined total of 404 hen locations was obtained over 1,352 days. No active nests were located at HWMA during this study and hens used forest stands differently between years. Seasonal activity ranges were 246.1 ha ± 187.9 ha and 437.0 ha ± 117.6 ha in 1999 and 2000, respectively, and were different between years (P = 0.032). Water levels were significantly (P = 0.000) different between years and were suspected to have influenced hen activity. This study proposes that managers inventory cavity availability in forest stands to identify important cavity producing trees. Low cavity densities exist in forest stands at lower latitudes and sound management must be implemented to promote and retain cavity trees. Additional research is needed to quantify the effect of water levels and habitat conditions on wood duck use of forest stands.