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

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