Notice that more and more ducks seem to be migrating through Minnesota after the season has closed?
Perhaps your impressions are correct, according to a new study by Delta Waterfowl that says many waterfowl are being taken by hunters significantly later in the year than in previous decades.
The Delta Duck Migration Study was written by Delta science director Dr. Frank Rohwer, Louisiana State University graduate student Bruce Davis and Delta's senior director of U.S. policy John Devney.
The US Fish and Wildlife Service has collected comprehensive harvest data from hunters since 1961, and the study examined data from its annual Parts Collection Survey.
"With few exceptions, harvest dates for mallards throughout the mid-latitude and southern states have become consistently later," Rohwer said in a Delta press release. "Mallard harvest is on average ten days later in Arkansas, fifteen days later in California, sixteen days later in Illinois, and twelve days later in Virginia."
Here's more from the release announcing the study:
Most migrant duck species, including gadwall, ring-necked, pintails and green-winged teal, have significantly later harvest dates now than historically has been the case. 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," says Rohwer. "As usual, hunters seem to know more than we give them credit for."
The report examined whether later hunting seasons were a simple explanation for later harvests. While it's true that most states have extended their seasons from the 60's, the report found this was not the 'sole driver' for shifts in harvest dates. For example, non-migrating mottled ducks in Texas and Louisiana are being harvested at about the same time as 50 years ago. But hunters in those states are harvesting mallards much later in the year, suggesting that Mallards – which are strictly migrants from the north - are arriving later.
So does a later harvest mean ducks are actually migrating later?
Dr. Rohwer says the best way to evaluate shifts in migrations would be a history of waterfowl counts throughout the flyways. Unfortunately, comprehensive fall migration surveys do not exist.
"The beauty of the Parts Collection Survey is that it has been conducted in the same manner since 1961 and records the date, location and species of duck killed. It provides a good general sense of when duck harvest is taking place, which we suspect is a reasonable surrogate for timing of migration."
A hot topic in southern duck blinds is whether changes in northern agriculture that provide additional food may be holding ducks longer in northern states. The theory goes that field-feeding ducks like mallards and pintails will stay longer; fatting up on left over corn and soy beans in higher latitudes.
If food was the driver of migration and harvest dates, says Dr. 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 the report.
The report also had a preliminary look at whether or not migration may be delayed because of the potential effects of climate change. While the report concluded it's 'plausible', the harvest data can neither prove nor disprove any connection between migration and climate change.
Waterfowl hunters are obviously interested in the timing of migrations, says Dr. Rohwer. The importance for the outdoor industry, tourism and waterfowl management make a compelling argument for more research into migration.
"Hunters, the outdoor industry and resource managers are not passive observers," says Dr. Rohwer. "They are expecting an answer to the deceptively simple question: Are ducks migrating later. They are holding policymakers and the scientific community accountable for an answer, as they surely should."
The Delta Migration Study is available in its entirety at on Delta Waterfowl's web site (www.deltawaterfowl.org/pressrelease/120529-MigrationStudy.pdf) or www.seasonsend.org.