Measuring Waterfowl Habitat- Population Changes from Aerial Photos

-.. .. _Measuring Waterfowl Habitat ~pulation Changes From Aerial Photos Harvey \IT. Miller Nebraska Game Commission Bassett, Nebraska A survey was conducted in 1953 to determine the feasibility of using aerial photography to measure the trends in available waterfowl habitat in the Nebraska Sandhills. This pilot survey included 96 one-square-mile sections systematically distributed over the area to give a 0.49 percent sampling rate. The basic waterfo\o1l habitat types apparent on the aerial photos of these sections were identified and measured with a planimeter and map measure. These ascertained totals were then projected to obtain the estimated total of each habitat type in the study area. A statistical analysis of the survey revealed that it would be necessary to use a sampling rate of approximately 22 percent rate in order to estimate the totals of each habitat type within an error not to exceed 5 percent of the estimated totals, Indications were that a 0.5 to 1.0 percent sampling rate would then be sufficient to measure the change in available habitat. Because of the magnitude of the survey required, this study was discontinued and no further attempt has been made to relate population trends to changes in the available habitat. MEASURING WATERFO~~ HABITAT POPULATION CHANGES FROM AERIAL PHOTOS Harvey W. Miller Nebraska Game Commission Bassett, Nebraska One of the major problems in waterfowl management is the determination of the trends in the breeding populations and in the habitat available to those populations. The surveys necessary to determine these trends must be extensive enough to produce reasonably reliable trend data yet fast, economical and simple enough to be accomplished by a small field staff. An ideal survey would not be subject to the discrepancies of human interpretation. This paper will report on a pilot study designed to determine the feasibility of using aerial photography to measure the trends in available waterfowl habitat B.nd the possibility of relating the trends in breeding populations to these habitat trends in Nebraska. The major waterfowl breeding grounds in Nebraska are the wetlands in the Sandhills region, an area of approximately 23,000 square miles of gently rolling to rough dune sands in the north-central part of the State. These 'Ioretlands are of several types ranging from temporary to more-or-less permanent areas, all of which are dependent upon runoff or ground-water levels. The average annual rainfall in the region ranges from 18 inches to 24 inches and may vary from less than 50 percent of average to more than 200 percent of average during any one year. Therefore, the amount of available habitat will vary considerably from year to year or even from season to season. . The major portion of the region is maintained as native mixed-prairie grasslands devoted to the production of cattle and hay. ~~st of this region is privately owned by large ranches. The human population is sparse and much of the country is isolated from all-weather roads. It was theorized that the size of the breeding population in Nebraska during anyone year could be directly correlated to the aroount of habitat available to that population at the outset of that breeding season. This was based on the assumption that, because Nebraska is on the southern limits of most species' breeding grounds, the ducks would completely occupy the available habitat and then move on north until, at the northern limits of the breeding grounds, they may become crol"ded to more than carrying capacity by limited available habitat or vica versa in relatively unrestricted areas. On the basis of this theory, a pilot survey was initiated in 1953 to . determine the feasibility of using aerial photography to sample the Sandhills breeding grounds. From these photos, the amount and extent of each type of wetlands would be measured as a basis for determining the trends in habitat available to the breeding populations. Subsequent surveys would then be designed to determine the relationship between trends in the population and this available habitat. Figure 1 shows an outline of the area included in the survey. This area contained 19,596 square miles and included the major portion of the Sandhi11s which contained significant amounts of wetlands.