Importance to waterfowl
As a consequence of alteration of hydrology and conversion of forest to agriculture, the current landscape in the MAV is highly fragmented and much drier than in historical times. It is dominated by agricultural land, some of which provides significant waterfowl habitat via flooding of waste grain, particularly rice and soybeans.
No data exist to estimate historical populations of migrating or wintering waterfowl in the MAV. Suffice to say that reliable winter flooding and abundant food resources in most years combined to make the MAV one of the most continentally significant areas of winter and migration habitat for several species, particularly mallards, wood ducks, gadwall, green-winged teal, American wigeon, and hooded mergansers (Reinecke et al. 1989). Reinecke et al. (1992) used aerial transects to estimate at least 1.1-1.8 million mallards, or approximately 17-29% of the breeding population, wintered in the MAV during winters of 1987-88 and 1988-89. However, these data were collected when mallards and many other species of ducks were at historically low population levels resulting from extended drought on prairie breeding areas in the 1980s (Reynolds 1987).
In 1999, the mid-continent mallard breeding population was estimated at 10.8 million, a 41-48% increase from the late 1980s (Wilkins and Cooch 1999). Applying that increase to the estimates derived by Reinecke et al. (1992) suggests that perhaps 1.6-2.7 million mallards wintered in the MAV in 1998. There are no other statistically valid surveys performed to estimate winter populations of mallards or other species in the MAV. However, harvest of mallards from the MAV states, including TN, KY, AR, MS, LA (including portions of those states outside of the MAV) during 1998 was estimated at 1.68 million. Assuming a very high harvest rate of 0.25 (which should lead to a conservative population estimate), as many as 4-5 million mallards may have wintered in this region. Hence, based upon past surveys, estimated breeding populations, and estimated harvest, it seems reasonable to conclude that at least 1.1 and perhaps <4 million mallards may winter in the MAV in some years, representing 17-40% of the estimated 1999 mid-continent breeding population. Clearly, the MAV is the most important wintering area for mallards in North America. Further, Nichols et al. (1983) suggested that the overall importance of the MAV to wintering mallards increases with winter severity and in wetter than average winters when habitat conditions are best.
The MAV is also a continentally important area for breeding and wintering wood ducks (Bellrose and Holm 1994), and following widespread conversion of forested wetlands to agriculture, has become more significant to northern pintails, green-winged teal, and northern shovelers, as well as snow and white-fronted geese. Catahoula Lake, a 12,150 ha basin that lies within the MAV, provides habitat to peak populations of 400,000 ducks. Catahoula Lake is particularly important to early migrant blue-winged teal and northern pintails, with September/October concentrations of 150,000-300,000 occurring in most years. Additionally, it has wintered up to 128,000 canvasbacks, which is the largest concentration in the world (LDWF unpublished data). Catahoula Lake and the Lower Mississippi River Delta (Gulf Coast Conservation Region) combined winter 10-25% of the continental population of canvasbacks.