Anew study has confirmed what veteran duck hunters have long suspected — hunting season is significantly later in the year these days than it was decades ago.
Delta Waterfowl science director Frank Rohwer looked at migration dates by examining data from the annual Parts Collection Survey that has gathered comprehensive harvest data from hunters since 1961.
“With few exceptions, harvest dates for mallards throughout the mid-latitude and southern states have become consistently later,” said Rohwer.
“Mallard harvest is on average 10 days later in Arkansas, 15 days later in California, 16 days later in Illinois, and 12 days later in Virginia.”
The study found most migrant duck species, including gadwall, ring-necked, pintails and green-winged teal, have significantly later harvest dates. Blue-winged/cinnamon teal and mottled ducks were the only species to run against the trend.
“Hunters have suspected this was happening, and for the first time, we’ve seen the data that confirms this on a big scale,” said Rohwer. “As usual, hunters seem to know more than we give them credit for.”
The study is a “pretty accurate assessment” of what’s been happening in the past three years, said Frank Baldwin, game bird manager for Manitoba Conservation.
“The big question is whether it’s a short-term blip, or a long-term variation,” said Baldwin, adding that it’s not unprecedented for birds to linger longer in the North’s myriad sloughs and grain fields during wet, mild fall seasons.
Ducks are forced to migrate south as their aquatic feeding areas freeze over. If the water stays open longer, they have no compelling reason to pull up stakes, he said.
But some species take their cue from autumn’s shorter days — a trait shared with fur-bearing animals. Blue-wing teals head south early in fall even when open water is ample, but Canada geese and mallards prefer to wait until the last possible moment, said Baldwin.
Climate change proponents point to problems with winter roads in the North, and anecdotal evidence gathered by native and Inuit hunters that the North is warming up.
While there is “good consensus” that migratory patterns have changed in the past 50 years, that’s not a long enough period to be proof of global warming, said Baldwin.
“We could easily have a really early freezeup this year,” he noted.
Rohwer’s report states climate change is a “plausible” explanation, but the harvest data neither proves nor disproves any connection between migration and climate change.
The food supply is another suspected factor, with the theory being that field-feeding ducks, such as mallards and pintails, are staying longer in order to fatten up on leftover corn and soybeans in higher latitudes.
If food was the driver of migration and harvest dates, said Rohwer, then gadwall and ring-necked ducks that never feed in fields should migrate and be harvested at the same time as in prior decades. The harvest data, however, shows that all four species show similar shifts in delayed harvest. The idea that northern agriculture is holding ducks back is “unlikely,” concludes his report.