Geology topics

Michael W. Brown

Publications and source records attributed to Michael W. Brown.

3 recordsLinked to original sources

USGS1997

Evaluation of a mallard HSI model for the Lower Mississippi Valley

We evaluated a habitat suitability (HSI) model developed for mallards ( Anas platyrhynchos ) wintering in the Lower Mississippi Valley by comparing mallard densities obtained from aerial surveys with habitat suitability indices derived from satellite imagery for 25, 256km 2 sampling units. Regression models that related mallard densities to habitat suitability indices accounted for only 29% of the variability in the data and the 95% confidence interval of predicted mallard densities included zero for most habitat suitability indices evaluated. Thus, we conclude that the published HSI model is a poor predictor of wintering mallard density in the Lower Mississippi Valley. We suggest model revision to allow users to remotely obtain model inputs for habitat characteristics at landscape scales. Further, we suggest the model be revised to consider yearly variation in habitat and flood conditions that better reflect the ability of an area to support wintering mallards.

Arkansas, Louisiana, Mississippi↗

USGS1995

Factors affecting visibility rate of aerial waterfowl surveys in the Mississippi alluvial valley

Because visibility bias can confound attempts to detect changes in abundance, we evaluated factors that affect visibility rate in aerial surveys of wintering waterfowl. We placed waterfowl decoys in 32 2- x 0.25-km strip transects in the Mississippi Alluvial Valley (MAV) during February 1990 and 1991 and observed the decoys under different experimental conditions. Visibility rate was influenced ( P < 0.10) by habitat, transect width, and decoy group size. We simulated variation in use of habitat and found that changes in use between open and wooded wetlands would cause changes in visibility rate and affect the power to detect a change in abundance. The effect of changes in visibility rate on likelihood of detecting population change depended on the magnitude and direction of population change and precision of the population index. For transect surveys of wintering ducks in the MAV we recommend reducing transect width from 250 to 150 m on each side of the aircraft and restricting comparisons between years when 70% of the population is likely to be distributed in open wetlands. Improved techniques for estimating abundance of wintering waterfowl are also needed so use of questionable population indices can be avoided.

Mississippi↗

USGS1992

Evaluation of aerial transects for counting winter mallards

Winter waterfowl surveys rarely use sampling methods, and little is known about the precision and biases of their population estimates. Consequently, we developed aerial transect surveys (n=5) in 4 strata comprising 16 substrata in the lower Mississippi Alluvial Valley during winters 1987-88 through 1989-90 to estimate mallard ( Anas platyrhynchos ) population indices and determine regional patterns of habitat use. Mallard population indices ranged from 1,147,628 (SE=192,341) in December 1988 to 1,790,708 (SE=179,406) in January 1988. Coefficients of variation (CV's) for early winter surveys averaged 0.15 and those for late winter surveys averaged 0.10. During early winter, 59-69% of mallards were on wetlands with water regimes managed for waterfowl; whereas in late winter, 52-79% used wetlands with unmanaged water regimes. Late winter was wet during 1987-88 and 1988-89, and most mallards (62-68%) were on naturally flooded croplands. Use of forested wetlands (3-11%) and moist-soil habitats (3-29%) varied among surveys but was not correlated with water conditions. The number of mallards using naturally flooded croplands (e.g., >1,100,000 in Jan 1988) illustrated the extent of habitat use on private lands. We recommend transect surveys (e.g., 5-yr intervals) for evaluating responses of mallard populations to management programs and as a sampling framework for integrating regional waterfowl research and management data.

Arkansas, Illinois, Kentucky, Louisiana, Mississip↗