Migration of birds of all species north and south is very different than it was a decade or two ago. That's well-documented for waterfowl in particular in a story in the most recent edition of the magazine Delta Waterfowl sends to members.
The story reports results of study of hunting statistics for the past 25 years.
“What we found,” said Dr. Frank Rohwer, president of Delta Waterfowl, “was a phenomenal later shift in the harvest of migrating ducks in the mid-latitude and southern states.”
The information indicates that the birds are migrating later, although Dr. Rohwer did not come right out and say so.
He used Kansas as an example. Average harvest date for Mallards in 1961 was Nov. 7. That date shifted to Dec. 5, 28 days later, in 2008-2009. For duck species resident in those southern hunting areas, birds that would not be migrating, harvest-date patterns were unchanged.
Ducks are staying later into the fall and winter seasons in North and South Dakota, which is why harvest dates to the south are becoming later. In January 2012 a record number of ducks and geese were counted in North Dakota. The article said that lack of snow cover was the primary reason the birds had not moved south.
In South Dakota a similar situation was seen. Nearly a million birds were found during a January 2013 survey.
“Those midwinter numbers and the motivation for waterfowl to migrate south are driven by the amount of snow cover, open water, and periods of cold temperatures,” Dr. Rohwer was quoted as saying.
Is it that climate no longer pushes the ducks south at historic dates? Or, for southern hunters, is it that the ducks don’t get down to them, not having to go as far south to find open water and food (which is climate-related).
The question: Is it climate change or habitat change? Biologists believe it is both.
At Sand Lake National Wildlife Refuge in northeastern South Dakota later migration of geese is more obvious than such for ducks. That information comes from refuge biologist William Schultze.
“Since I began working here in 1976,” he wrote in an email, “the average peak of the Snow Goose migration has shifted from late October to near mid-November.
“I see changes in agricultural practices in North Dakota and Canada as the primary reason for that shift,” he said. “One other factor that might be considered is the amount of wetlands available, at least in northern South Dakota, since the mid-1990s. The larger wetlands that remain open longer can hold a lot of ducks and geese,” he said.
Goose movement was heavy after Nov. 21 at Sand Lake, the date refuge lakes froze over. The number of Snow Geese reported on the refuge on Nov. 20 was 130,000, with 125,000 ducks and 5,000 geese estimated. Five days later the number of Snow Geese was 400, Canada Geese 3,500, ducks 18,000, and swans zero.
This photo of Snow Geese was taken at Sand Lake NWR.