Whooping Crane Migrational Habitat Use Draft (2)

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DISCUSSION Detection Rates One of the primary objectives of the whooping crane monitoring protocol was to monitor the frequency and spatial distribution of whooping cranes in the study area. The detection trials conducted to date offer evidence of detection probabilities less than 100% and significant variation in the probability of detection for whooping cranes in the study area, indicating our analyses should account for the detection probability. The estimation of this detection bias enables the calculation of unbiased estimates of trend and unbiased resource selection models. Detection trials conducted during each survey resulted in the most reliable estimates of the probability of detection for each field season. Detection trials conducted for each survey reduced the impact of changes made to the survey protocol during the period of study. Movement Patterns The main purpose of conducting the movement pattern analysis was to determine a value for use in defining a local area for selection. This purpose was achieved. However, in conducting the analysis it was found that the average movement distance of 3.2 miles corresponds, coincidentally, to the study area width established in the monitoring protocol of 3.5 miles either side of the main channel centerline. If crane groups being monitored move outside this study area the field crews made a professional judgment on whether or not the cranes were migrating from the Platte River area. If the crane group was judged to be migrating from the area, ground crews stopped observations. If the crane group was judged to be temporarily using habitat outside the primary study area the ground crew continued to make observations. It appears that the Program's defined monitoring corridor will capture the majority of out-of-channel crane use locations. Notwithstanding, if cropping/farming or habitat patterns change this local area selection figure may increase (possibly indicating that cranes are moving further to feed or between roosts) or decrease (possibly indicating increased habitat availability to the cranes). Index of Use The index of use was calculated to determine the trend in crane use in the study area. The variability in survey effort was accounted for in estimating the trend in use. Thus, regardless of differences in effort among survey years an increase in the index of use over time should represent a real increase in crane use of the study area and a decrease in the index over time should indicate a real decrease in use of the study area. There was no statistically significant positive or negative trend in the index of crane use of the study area from 2001 to 2006. That is, while there were annual fluctuations in the number of birds observed, over time there was no change in crane group use, despite an increase in size of the Aransas-Wood Buffalo migrating population during this same time. It is difficult or impossible to determine what, if anything, a non-significant trend in the index of use means in a biological sense. Although this study did not address the cause of the observed trend, different hypotheses could include: the trend was real but small, the study area is saturated 15