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Table 1 Definition of variables used to explain the probability from stopover sites by autumn-migrating dabbling ducks from 1995 to 2009

From: The effect of weather on the decision to migrate from stopover sites by autumn-migrating ducks

Variable Name Variable Definition
Winds aloft index Binary description of the direction of winds aloft at an elevation within the known cruising altitude of ducks in this region (433 m above ground level [26]). Favorable winds (1) are those that are following relative to the preferred direction of departure from study site 151.8° ± 0.71° (mean ± se), and unfavorable winds (0) are those that are opposing.
Precipitation index Binary description of precipitation status with 1 = No precipitation observed at time of departure (2300 GMT), 0 = Precipitation observed at time of departure
Cloud cover Proportion of the sky covered by clouds at time of departure (0/8–8/8)
Cloud cover index Binary index describing the amount of cloud cover. When stars were completely obscured (8/8 cloud cover), an index of 0 was assigned; If at least some portion of the stars were visible (0/8–7/8 cloud cover), an index of 1 was assigned
Cloud height index Binary index of cloud ceiling height with 1 = Cloud ceiling> 600 m AGL and 0 = Cloud ceiling< 600 m
Temperature Surface air temperature at time of departure (°C)
Difference in daily mean temperature Difference in mean daily temperatures (°C) between the 24-h period immediately preceding a departure/non-departure event and the 24-h period prior to that day
Minimum daily temperature Minimum daily temperature (°C)
Barometric pressure at dusk Barometric pressure at dusk (mb)
Change in barometric pressure Change in barometric pressure from 6 h prior to departure (1700 GMT) to time of departure (2300 GMT)
Foraging habitat index Qualitative index of waterfowl food production measured within study area in August/September with 0–2 = no or poor food production, 3–4 = fair, 5–6 = good, 7–8 = very good, and 9–10 = excellent [NA = Not available]
Surface wind speed The rate of horizontal travel of air past a fixed point (m/s)
Julian date Julian date