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Delta Waterfowl study has confirmed what veteran duck hunters have long suspected: harvests of many waterfowl are taking place significantly later in the year than in previous decades.
The Delta Duck Migration Study, commissioned by the Bipartisan Policy Center, was written by science director Dr. Frank Rohwer, Louisiana State University graduate student Bruce Davis and senior director of U.S. policy John Devney.
The study examined data from the annual Parts Collection Survey. The U.S. Fish and Wildlife Service has collected 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," Dr. Rohwer said. "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 that 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," Rohwer said. "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 said 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, Dr. Rohwer said, 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,' the report concluded.
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, Dr. Rohwer said. 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," Dr. Rohwer said. "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, DeltaWaterfowl.org or SeasonsEnd.org
Delta Waterfowl Foundation is a leading North American conservation organization, tracing its origins to the birth of the wildlife conservation movement in 1911. The Foundation supports research, provides leadership and offers science-based solutions to efficiently conserve waterfowl and secure the future of waterfowl hunting. Delta Waterfowl is based in Winnipeg, Manitoba, and Bismarck, N.D.
