California Duck Hunting Forecast

“Our results indicate that among the tested environmental parameters, the dominant environmental driver of departure decision in autumn-migrating mallards was the onset of snow conditions, and secondarily the onset of temperatures close to, or below, the freezing point.”

Snow first, the freeze second Snow arriving is the strongest driver of a mallard leaving in autumn, and temperatures at or below freezing the next strongest.

“Among recorded departures, most were driven by snow days (65%) followed by current temperature (30%).”

Two departures in three followed snow days Most recorded departures came after consecutive days of snow on the ground, and most of the rest after the day turned cold.

“Departure was best predicted (60% accuracy) by a "winter conditions" model containing temperature, and depth and duration of snow cover. Models conditional on wind speed, precipitation, pressure variation, and cloud cover received lower support.”

Winter conditions ranked first, the barometer last Among collared mallards the best model held temperature with the depth and duration of snow cover, and wind speed, precipitation, pressure change and cloud cover all ranked below it.

“MSU and Missouri collaborators found that cumulative effects of snow and temperature, as well as the duration of these events, best explain the rate of change in duck abundance.”

Snow and cold added up over days What explains the change in duck numbers is snow and temperature accumulated over consecutive days, not one cold morning.

“Number of sequential days of snow depth ≥ 2.54 cm (1 inch) experienced by mallard at this location”

What counts as a snow day A snow day is one of a run of consecutive days with at least an inch of snow on the ground.

“Our results indicate that among the tested environmental parameters, the dominant environmental driver of departure decision in autumn-migrating mallards was the onset of snow conditions, and secondarily the onset of temperatures close to, or below, the freezing point.”

Snow first, the freeze second Snow arriving is the strongest driver of a mallard leaving in autumn, and temperatures at or below freezing the next strongest.

“dabbling ducks, including northern pintail, gadwall and green-winged teal, migrate prior to freezing conditions or snow, while mallards generally migrate when freezing temperature and snow persist for several days”

Early ducks leave ahead of the freeze, mallards after it Pintail, gadwall and green-winged teal move before freezing weather arrives. Mallards generally wait until the freeze and the snow have held for several days.

“In the past few years, we have observed that ducks are not migrating to southern latitudes in abundance, or are doing so generally only in the presence of severe weather”

Big flights need real weather Ducks reach southern latitudes in numbers mainly when severe weather pushes them there.

“explained 40% of the variation in change in relative abundance of mallards and other dabbling ducks in Missouri during autumn–winter of 1995–2005.”

The index explains two fifths of the change The published weather severity index accounted for 40 percent of the change in dabbling duck numbers across eleven autumns and winters in Missouri.

“The best approximating model of departure probability was our integrated model, which included variables accounting for wind aloft direction favorable for departure (i.e., tailwind), absence of precipitation, and a partially or completely clear sky.”

A tailwind, dry air and a clear sky The model that best predicted a duck leaving a stopover combined a favourable tailwind aloft, no precipitation, and a partly or completely clear sky.

“Our results indicate that among the tested environmental parameters, the dominant environmental driver of departure decision in autumn-migrating mallards was the onset of snow conditions, and secondarily the onset of temperatures close to, or below, the freezing point.”

Snow first, the freeze second Snow arriving is the strongest driver of a mallard leaving in autumn, and temperatures at or below freezing the next strongest.

“MSU and Missouri collaborators found that cumulative effects of snow and temperature, as well as the duration of these events, best explain the rate of change in duck abundance.”

Snow and cold added up over days What explains the change in duck numbers is snow and temperature accumulated over consecutive days, not one cold morning.

“Tailwind was documented as the primary weather condition affecting the propensity for migration in many bird species, including ducks, due to its substantial effect on the net energetic cost of migration”

The wind pays for the flight Tailwind is the flight condition that matters most across migrating birds, because it decides what the journey costs.

“The best approximating model of departure probability was our integrated model, which included variables accounting for wind aloft direction favorable for departure (i.e., tailwind), absence of precipitation, and a partially or completely clear sky.”

A tailwind, dry air and a clear sky The model that best predicted a duck leaving a stopover combined a favourable tailwind aloft, no precipitation, and a partly or completely clear sky.

“Flight weather is a prominent migration driver in passerines, but with the notable exception of wind direction, it plays less of a role in waterfowl.”

Wind direction is the one flight factor that carries Flight weather drives songbird migration more than it drives waterfowl, and wind direction is the exception that still counts.