The spatial and temporal patterns of migration substantially influence the ecology and conservation of ducks. For the most part though, the processes that affect when a duck leaves and where it goes remain poorly understood due to the difficulty of investigating movements that occur over large spatial scales, at substantial heights and at night. We recently demonstrated how weather surveillance radar (WSR) can be used to detect and identify migrant ducks as they leave isolated stopovers. Herein, we apply WSR to monitor the egress of ducks from a wetland complex along the Illinois River during the falls of 1995–2009, and examine the effect of weather on the presence or absence of migration among nights. An evaluation of competing models indicated following winds aloft, no precipitation, less cloud cover, decreasing temperatures, increasing barometric pressure and date best predicted emigration (R2 = 0.52). Based on this model, the odds of a duck emigration occurring when winds were following and precipitation was absent were 13.2 to 1.0 (95% CI 7.8–22.4). Upon departure, ducks must endure conditions aloft and orient to another suitable stopover. Though advanced orientation capacities have been documented in other avian taxa, the notion that ducks rely on the leading-lines of rivers for visual orientation has remained a dominant paradigm in waterfowl science. We used WSR to examine departure tracks of duck emigrations from our study area along the Illinois River from 1995 to 2009 and found ducks had a significant SSE directional preference (152°; P < 0.05), which differed significantly in all years from the course of the Illinois River (220°; P≤ 0.001). This pattern was markedly different than the river-oriented route described for ducks departing this site in the mid-20th century. Thus, leading lines appear to have been unimportant for orientation in the majority of duck emigration events from the major stopover area examined here.
|Name||INHS Technical Report 2010 (16)|