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Redheads are unique among North American duck species. Nearly 80% of all redheads in North America are concentrated in winter on two highly saline lagoons along the western rim of the Gulf of Mexico, the Laguna Madre of Texas and the Laguna Madre of Tamaulipas, Mexico. Field station scientists have investigated many aspects of redhead winter ecology, including distribution and abundance, habitat use, foods and foraging ecology, trace element contaminants, feeding behaviors and time-activity budgets, nutrient reserves, stable isotope composition in body tissues and foods, mineral composition of flight feathers, molt status, and salt gland development.
Redheads in winter depend very heavily on rhizomes of shoalgrass, a species of seagrass. From the arrival of the first redheads in October to the departure of the last birds in March, about 80% of the diet of redheads wintering in southern Texas consists of shoalgrass rhizomes. Dependence of redheads on shoalgrass rhizomes is apparently a continuing, long-term phenomenon.
Redhead ducks use both saltwater habitats of the Laguna Madre and nearby freshwater wetlands on the adjoining mainland and barrier islands. Sharply distinct differences in use of the two types of habitat are apparent; nearly all feeding occurs in salt water, and nearly all drinking occurs in fresh water. Ponds serve as sources of drinking water for redheads feeding in the highly saline Laguna Madre. Both coastal ponds and the Laguna Madre must be considered as vital parts of the Texas winter range of redheads. The continued integrity of the Laguna Madre of Texas and the Laguna Madre of Tamaulipas as functional ecosystems is essential to the maintenance of the western Gulf of Mexico as the major winter range of this species of migratory waterfowl.
Most important among current issues are open-bay disposal of sediments from maintenance dredging of the channel of the Gulf Intracoastal Waterway in the Laguna Madre of Texas, and its subsequent effect on light transmission and seagrass photosynthesis. Other prominent issues highlighted by the close linkage between redheads and shoalgrass are the potential re-emergence of brown tide in the Laguna Madre and its effect on light transmission and the continuing widespread decline of shoalgrass meadows. Further decline in shoalgrass in the Laguna Madre could even lead to a population crash. Current focus is therefore on development of a redhead population model. A number of long-term data sets of redhead numbers and habitat conditions are used to construct a conceptual redhead model with Laguna Madre (winter range) and prairie pothole (breeding range) subcomponents. This conceptual model provides the framework for generating other hypotheses with which to test interactions of redhead population numbers and habitat conditions.
Stable Carbon Isotopic Composition of Redheads On Their Breeding and Wintering Ranges (.pdf file)
ABSTRACT: We investigated ð13C values of breast and leg muscle, liver, gizzard, and abdominal fat from 259 Redheads obtained from the Texas winter range, South Dakota breeding grounds, and from a molting lake in Manitoba. We also measured ð13C values of representative aquatic biota, including known Redhead foods, from these areas. We tested the hypothesis that, as Redheads change from a seagrass diet in winter, to a mixed diet while breeding, and then to a postbreeding diet of submerged aquatic vegetation, the isotopic composition of their tissues will change also. Tissue ð13C values, which were highest for winter birds (range = -10.0 to -13.1 ppt) and lowest for breeding birds (range = -22.4 to -28.7 ppt), changed seasonally to reflect altered isotopic composition of diets.
U.S. Fish and Wildlife Service, Region 2
Texas A&M University-Corpus Christi, Center for Coastal Studies
The Nature Conservancy of Texas
Redhead breeding grounds in the prairies potholes of North America.
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