New Snow Modeling Study Indicates Some Waterfowl Hunting May Have to Migrate North

Michael Notaro and David Lorenz of the University of Wisconsin-Madison’s Center for Climatic Research, Christopher Hoving of the Michigan Dept. of Natural Resources and Michael Schummer of Long Point Waterfowl recently published an analysis of future snowfall in the eastern US, covering the range of 10 LCCs including the GCPO LCC.  They used statistically downscaled output from 9 global climate models (GCMs) to develop projections of snowfall, snow depth, and winter severity using the SNOW-17 model under the contrasting high-end A2 and low-end B1 emission scenarios.  They found that for every location in the study region, warming is a robust projection for December-March (DJFM) under both emissions scenarios.  This means less snowfall in most cases, which, along with projected snow depth, the authors used to calculate a decrease in the cumulative winter severity index (CWSI), which is known to influence autumn-winter waterfowl migration.

Huh? Just what does this alphabet soup really mean for waterfowl?  

To answer that question, we need to unpack this meteorological shorthand just a bit.  

We all know that recent climate change is primarily occurring due to an increase in greenhouse gas emissions into the atmosphere from fossil fuels and other sources, but the future rate of emissions will vary dependent upon the actions of society and governments worldwide.  The A2 and B1 emissions scenarios represent one of the highest and one of the lowest projected accumulations of greenhouse gases respectively, widely used by scientists around the world.  Overall, greenhouse gas concentrations increase under both scenarios during the 21st century.

To anticipate how weather is likely to change as a result of these emissions, geophysical and meteorological scientists have developed sophisticated global climate models or GCMs that provide projections about things like daily maximum temperature, minimum temperature and precipitation, which can be downscaled across regions such as North America.

However, a GCM gives only coarse information about snowfall and none about snow depth.  To do this requires a model of snowfall, in this case the SNOW-17.  The SNOW-17 is fed information from the global climate models, which varies according to the greenhouse gas emissions scenarios (A2 and B1).  Running the SNOW-17 model provided snow simulations showing the projected amount of snowfall and snowpack accumulation under each scenario.

Snowfall and accumulation: the missing piece of the puzzle

Why are these data important to waterfowl?  The severity of winter, winter storms and degree of snowfall and accumulation are known to influence autumn-winter waterfowl migration from Canada into the northern and southern parts of the U.S.  That autumn migration is all-important to the $3.4 billion migratory bird hunting industry in the U.S., as well as all the folks who just plain love to hunt and view waterfowl.  In Mississippi alone, waterfowl hunting generates $86.6 million annually while annual expenditures for wildlife watching in the state exceed $175 million. (2006 National Survey of Fishing, Hunting and Wildlife Associated Recreation, USFWS).

Michael Schummer has developed a winter severity index, or WSI, that uses historic waterfowl and weather data from 1979-2012 over all of eastern North America to calculate a species threshold relative to the location and timing of fall migration.  “The threshold represents the point in time when the severity of weather is great enough to cause abundance of mallards to decrease at northern or mid-latitudes and move into more southerly latitudes,” said Schummer.  The WSI plots the line of the threshold for a declining number of mallards dependent on weather inputs such as snow, cold temperatures and ice.  “The threshold tells resource managers how many square kilometers in Missouri, for example, are above or below the threshold, and they can use that information to compare with recreational user days, harvest, etc.”  

Michael Notaro’s and David Lorenz’s climate modeling work has essentially put the WSI into the business of making future predictions about mallard migrations.  “My collaborators were the first ones to do this,” says Schummer.  “I could not come up with WSI projections without some estimate of future changes in snow cover and depth.  That is what the SNOW-17 model provided.” 

Notaro used cold-season air temperature and snow depth projections to calculate a cumulative winter severity index (CSWI) for the 10 LCC regions.  Under both future carbon emissions scenarios, the regional trend towards fewer snow days and even greater decrease in snow depth translates into a dramatic decrease in the winter severity index.  They have developed an interactive online mapping site for plotting the change in climate and snow projections over the next century.  

What does this mean to you if you are a hunter, or simply enjoy the spectacle of autumn waterfowl migration?

What does this mean for ducks?  The bottom line is that the winter climate conditions that seem to trigger autumn mallard migration into the US from Canada could be delayed by up to a month by the late 21st century.  This means that over the course of the next eight decades, the timing of mallard migration may become less predictable and progressively later in the year, effectively reducing the length of a relatively short waterfowl hunting season. 

“We’re already seeing that in some years mallards don’t migrate much until the second week of January, which means ducks are plentiful for the last two weeks of a possible 60-day season.  Those are frustrating years,” said Schummer.  

In addition, despite last winter’s harsh conditions, the trend is for the Great Lakes to freeze later and receive less snowfall.  The Great Lakes may well become the new area for concentrations of overwintering waterfowl.  However, Schummer cautions there is still some genetic influence in waterfowl migration such that there will still be birds that follow the traditional pattern of overwintering in the southern part of the Mississippi Flyway.  “It’s possible that this migratory change might not take hold as much as we think it will.”  Meanwhile, delays in waterfowl migration are already occurring and are likely to continue.

This research was funded by the Gulf Coastal Plains & Ozarks LCC, the Upper Midwest & Great Lakes LCC, Wisconsin Focus on Energy, and the US EPA’s Great Lakes Restoration Initiative through a contract with the Michigan Dept. of Natural Resources.  It is part of a larger project entitled “Factors Influencing Autumn and Winter Distribution of Dabbling Ducks in the Atlantic and Mississippi Flyways of North America.”  The project will also support a graduate thesis and several more follow-up publications calculating future WSI for other species of dabbling ducks.  Mike Schummer has also developed a web application tool that allows other researchers access to WSI waterfowl data for 1979-2012 for other types of analyses.  For more information, contact Mike Schummer at mschummer@longpointwaterfowl.org.

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Tags: 17, Hunting, Migration, Modeling, New, SNOW, Snow, Study, WSI, Waterfowl, More…index, mallard, severity, winter

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