Limnological Conditions Influencing Duckling Use of Saline Lakes in South-Central North Dakota

Abstract

The distribution of ducklings on North Dakota saline lakes and their tolerance of these waters under controlled conditions were investigated. Sulfates dominated the anions and sodium, magnesium, and potassium the cations of the lakes investigated. Salt concentrations are altered by changes in water volume and construction-induced hydrologic barriers that change the natural water flow and mixing. Hydrologic characteristics of saline lakes dictate the limnological conditions that influence duckling use by controlling salt concentrations, the availability of fresh water, and aquatic foods. Ducklings were closely associated with fresh inflow from spring seepages or adjacent wetlands of low salt content. Ducklings that used sheltered bays with chemically stratified water were able to feed on fresh water. Ducklings <1-3 days of age experienced some mortality at 16 mmhos/cm and could not tolerate salt concentrations in prairie lakes that exceeded 20 mmhos/cm unless fresh water was also available. Salt concentrations of 17 mmhos/cm significantly reduced growth. High levels of magnesium and sulfates may cause greater stress on birds than equivalent concentrations of sodium chloride that are processed by the supraorbital salt glands. J. WILDL. MANAGE. 48(2):340-349 The prairie pothole region of North America contains a high density of shallow wetland basins that were formed by glaciation and developed under the influence of a semiarid climate. The hydrologic regimes of these basins dictate their chemical characteristics and subsequently the plant and invertebrate communities they support (Stewart and Kantrud 1971, Swanson et al. 1974). Lakes in south-central North Dakota that contain elevated salt levels function as hydrologic sumps, occur in low-lying basins, and are usually associated with glacial outwash or meltwater channels. The prairie pothole region supports a major segment of the annual continental waterfowl population, however, little is known of the response of breeding ducks to its saline lakes (Serie and Swanson 1976). Waterfowl are attracted to saline lakes where they feed on a variety of salt-tolerant invertebrates, vascular plants, and filamentous algae (Swanson et al. 1974, Serie and Swanson 1976, Krapu and Swanson 1978). Although adults are known to fly between freshwater sites and saline lakes where they feed, little information exists on the suitability of this type of habitat for ducklings. Female dabbling ducks nest on islands in permanent saline lakes (Duebbert et al. 1983) but the fate of the broods that they produce has not been determined. Current interest in the use of wastewater derived from irrigation return flows and geothermal effluent to develop waterfowl habitat requires more knowledge about waterfowl response to saline waters. Land-use practices can also increase salt levels of natural wetlands by initiating hydrologic changes. The objective of this study was to identify the limnological conditions that influence duck brood use of saline lakes. This paper details: (1) a description of the chemical characteristics of saline lakes in south-central North Dakota; (2) a survey 340 J. Wildl. Manage. 48(2):1984 This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 06:06:12 UTC All use subject to http://about.jstor.org/terms DUCKLING DISTRIBUTION * Swanson et al. 341 of their use by duck broods; and (3) exposure of incubator-hatched ducklings to their waters. Appreciation is extended to M. G. Barron, P. F. Springer, and J. F. Wolf for assistance in the field; D. H. Johnson for aid in statistical analysis; and H. F. Duebbert, A. B. Sargeant, and T. C. Winter for reviewing the manuscript.