We examined turnover and stopover duration in dabbling ducks at a major wetland complex in the Illinois River Valley during the fall. Using weather surveillance radar data collected at the KILX radar in Lincoln, Illinois, we estimated the total number of waterfowl emigrating from the study site throughout the fall migration in 2005 and 2006 (October-December). We estimated the average stopover duration across an entire migration by dividing estimates of total use-days (derived from INHS aerial inventories) by estimates of the total number of ducks departing the same site (derived from radar) for each year. We detected 20 departure events in 2005 totaling approximately 401,758 dabbling ducks, and 23 departure events in 2006 totaling approximately 601,968 ducks. Preliminary calculations indicate the average stopover duration for all dabbling ducks was 9 days in 2005, and 6 days in 2006. These initial calculations indicate that the duration of stopover among dabbling ducks in the fall may be substantially shorter than 28-day estimate used for JV mid-migration objectives. Additionally, we examined 3 wetland complexes in Illinois using weather surveillance radar data collected at KILX from October 1-December 31, 2005-2006 to determine the timing of discrete dabbling duck departures throughout each fall. We compiled a database of biologically-relevant weather observations and constructed a set of competing biological models that will be analyzed using an information theoretic approach to model variation in daily emigration probability and determine the magnitude of the effects of specific environmental conditions. Our initial analysis of radar-derived departure data revealed a high level of synchrony in the timing of departure among dabbling ducks from independent stopover sites. We also identified temporal clusters of departures that correspond with the 2-3 day cycles of regional weather in the Midwest. These two observations provide local, empirical evidence of a 3 measurable relationship between proximate environmental conditions and emigration in dabbling ducks. Our future analysis will quantify which weather conditions have the greatest effect on the probability of daily departure of ducks from stopover sites, and what the magnitude of their effect is.
|INHS Technical Report 2008 (18)