Aix sponsa
The striking male Wood Duck, probably the most attractive waterfowl in North America, is a favorite of hunters. This species constitutes more than 10% of the annual waterfowl harvest in North America, ranking only behind the much more common Mallard (Anas platyrhynchos). During the nineteen century many ornithologists worried about the demise of this duck because of excessive harvests and loss of habitat. But since the limitation of harvests after the passage of the Migratory Bird Treaty Act in 1916 and the erection of many nest boxes to replace lost natural cavities in wetland habitats, the population has increased steadily (Hepp and Bellrose 1995).
Wood Ducks are omnivores, feeding by dabbling on or under the water on seeds, fruits and aquatic invertebrates while in pairs or small groups. An unusual waterfowl, raising two broods per season, the species is considered the most successful of North America’s seven cavity-nesting waterfowl species (Hepp and Bellrose 1995).
DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, observers found 76 confirmed, 169 probable and 63 possible breeding sites. The highest concentration of breeding evidence was in the part of eastern Texas with average annual rainfall of one meter (40 in) or more, mostly in the Pineywoods, Post Oak Savanna and Blackland Prairies and eastern Coastal Prairies regions (see the region map in Lockwood and Freeman [2004]). Breeding sites became more scattered west and south of this area with few sites west of the 100th meridian and south of the 29th parallel, except for a small area in the northeast Panhandle.
Data from the North American Breeding Bird Survey (BBS) produced a map similar to the TBBA map with a relative abundance of <1 duck per route (Sauer et al. 2007). In Oklahoma atlasers found 11 confirmed and 60 probable breeding sites widely distributed through the state (Stuart 2004).
Most Wood Duck breeding occurs east of the Great Plains and in the Pacific Coast states and British Columbia (Sauer et al. 2007) and Cuba. In winter many northern breeders move south, some as far as central Mexico (Howell and Webb 1995, Am. Ornithol. Union 1998, Versaw 1998, Corman 2005).
SEASONAL OCCURRENCE. Wood Ducks are resident in Texas with breeders in the Panhandle generally moving southward in winter as other migrants arrive from the north to winter in the warmer parts of the state. Breeding in Texas occurs from mid-February to early September, based on egg collection dates from March 1 to July 15 and half-grown young seen as late as August 25 (Oberholser 1974, Lockwood and Freeman 2004).
BREEDING HABITAT. Wood Ducks breed in Texas from near sea level to about 1100 m (3500 ft) in wooded areas bordering slow-moving streams, swamps, ponds, lakes and reservoirs (Oberholser 1974). Colorado atlasers found breeding evidence mainly in deciduous riparian woods, and woodlands around lakes and marshes with cattails (Versaw 1998). The few records in Arizona came from similar habitats (Corman 2005).
Wood Ducks nest in natural cavities in trees and in nest boxes. Holes excavated by Pileated Woodpeckers (Dryocopus pileatus) may also be used. The most suitable natural cavities form when a large branch breaks off from a tree at least 30 cm (12 in) in diameter, but usually at least 60 cm (24 in), allowing heart rot to reach the trunk. A usual cavity opening is about 30 cm wide and 60 cm high (12 x 24 in). The height of the nest above the ground or water varies widely, determined by the height of available cavities. Although lower cavities are preferred, in one study the average height was 7.3 m (24 ft; Harrison 19979; Hepp and Bellrose 1995).
The cavity lining is down feathers from the female’s breast (added during egg-laying). She usually lays 9-11 white to dark tan eggs, one per day. Cavities with 40 or more eggs have been reported, but clutches of more than 15 are considered “dump nests,” usually not incubated by any of the females (as many as 5) involved. Females incubate active nests for 28-31 days (see Harrison [1979] for a picture of the cavity lining and eggs). The newly hatched precocial ducklings jump from the nest to the ground or water the morning after hatching, dropping as far as 69 m (227 ft) without injury. The female gathers and broods the young for several weeks. The young feed on invertebrates before switching to plant foods. (Hepp and Bellrose 1995).
STATUS. Wood Ducks are locally common in eastern Texas, becoming uncommon further west (Lockwood and Freeman 2004). The distribution of breeding and summer symbols on the map in Oberholser (1974) is not noticeably different from the TBBA map. BBS data from 25 routes suggests a +4.7% annual population change for 1980-2006 in Texas, similar to a +3.1% change in Oklahoma and a statistically significant +3.5% population trend for North America (Sauer et al. 2007). These trends are encouraging for the future of this duck in Texas.
Text by Robert C. Tweit (2008)
Literature cited.
American Ornithologists’ Union. 1998. Checklist of North American birds, 7th ed. Am, Ornithol. Union, Washington, DC.
Corman, T. E. 2005. Wood Duck (Aix sponsa). In Arizona breeding bird atlas. pp. 54-55 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.
Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.
Hepp, G. R. and F. C. Bellrose. 1995. Wood Duck (Aix sponsa), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from: http://bna.birds.cornell.edu/bna/species/169doi:1
Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, New York.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Oberholser, H. C. 1974. The bird life of Texas. University of Texas Press, Austin.
Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 7.23.2007. USGS Patuxent Wildlife Research Center, Laurel MD < http://www.mbr-pwrc.usgs.gov/bbs>
Stuart, R. A.. 2004. Wood Duck (Aix sponsa). In Oklahoma breeding bird atlas, pp. 64-65 (D. L. Reinking, ed.). University of Oklahoma Press, Norman.
Versaw, A. E. 1998. Wood Duck (Aix sponsa). In Colorado breeding bird atlas, pp. 70-71 (H. E. Kingery, ed.), Colorado Bird Atlas Partnership, Denver.