Wednesday, December 28, 2011

When (and Why) Waterfowl Don't Migrate South

These geese, while spooky to hunters (and piling up next to public roads
since they expect blinds or pits to be in the middle of the field), were
still compelled to migrate south into this area (Maryland's eastern shore,
January 2011) because of deep snow in New York and Pennsylvania. 
It's almost January.  The waterfowl seasons in most states are at least half over.  This year, a situation has emerged that's actually not surprising, given that it's happened for probably 8 out of the last 12 years.  That situation: significant numbers of ducks and geese have not flown south for the winter.

Here in Maryland, the state DNR is reporting roughly 10% of the typical flock and "one of the worst seasons on record." News releases from other mid-latitude states show the same thing.   What's most surprising is that hunters seem aghast and totally confused that this is happening.  I'm here to tell you: it's pretty simple.

Many bird species are driven to migrate.  It is part of their internal programming.  There are two major parts of this programming - route and movement.  Route, for many species, is basically pre-determined.  For timing of movement, they often need prompting - a cue.  Sometimes it's as simple as the first full moon after a hard frost.  Or the first day that water temperatures rise above 60 degrees.    Speaking in huge generalities here, the spring migration tends to be more dominated by these cues than the fall migration.  And since hunting regulations are specifically structured to guard the safety of the spring migration, it's the fall migration with which hunters concern themselves.

So why do waterfowl migrate south in the fall? Again, sometimes a combination of internal programming and external cues cause a massive flight to occur.  But in the case of several species, and notably the Atlantic Flyway, migration is largely driven by necessity.  Specifically, the necessity of each living bird to maintain their own caloric balance.    With the exception of mating behavior, waterfowl are largely energy conservative species.  What does that mean?

To put it bluntly, it means that if 100,000 geese are doing the backstroke in 55 degree water in Lake Ontario, and eating corn off of the ground every night, why would they ever migrate south......even if it's December? Sound like an exaggeration?

That's right.  It's almost January, and there is almost no ice on the Great Lakes.  Which means there's little snow in the areas around the Lakes (we'll get back to that).  Many duck and goose species travel through the Great Lakes on their way to wintering spots in the Mid-Atlantic.  Does 50 degrees sound like really cold water?  According to Cornell University, water temperatures of 50-70 degrees are ideal (thermally neutral) for ducks, and it's widely written that large birds (ducks, geese, etc) are "heat neutral" down to about 55 degrees (air temperature).    So, sure, the birds are comfortably in this balmy early winter weather we seem to have most years anymore, but how does that impact migration?

You see, birds use 35-50% of their food intake solely for body temperature regulation.   As it gets colder, water bodies freeze, and snow cover starts to eliminate local feeding habitat, each bird must still somehow find 35-50% of their "summer ration" of calories, just to keep warm enough to survive until the next day.......or very likely die if they fail to eat enough calories.   What did I just say about snow?  Snow cover.  If there is a 3' layer of snow across all of New York state, very few birds will be spending the winter in New York state (and many who stay will die before spring).    Birds are hard pressed to try and find food in more than 1-2" of snow.  Let's look at a snow cover map - from a year (2010) when a hard freeze in mid-December forced a huge (though delayed) migration on the east coast, and from a year (2011) when no such freeze occurred, and the fall migration is still pending.
Christmas 2010 saw snow cover down to northern Arkansas.  Same date, 2011? New York, Pennsylvania, and most of the Great Lakes states are snow and ice free.  Are you still wondering why the birds aren't in North Carolina?

In a world without industrialized, large scale agriculture, birds could be forced south as they eat themselves out of their natural wetland habitat in a stopping point. But the eastern half of the United States is now filled with giant farms with waste grain laying about,  farms with green, delicious winter cover growing on them, and natural food sources (such as they are) available in wetlands and open water.   Until weather (ice, snow, cold air) changes the equation, there is no food shortage for North American waterfowl, except for those dependent on aquatic grasses (largely banged up by water pollution).  This is not to say there's no habitat shortage.
A flock of snow geese eating (destroying) a soil erosion cover crop.  The geese will stay until either the grass is gone,
hunting pressure is applied repeatedly, or snow cover makes it unavailable to the geese.  Migration south could take place after that point.   Photo:

The bottom line is this.  Many (though not all) species of waterfowl tend to be energy-conservative.  As long as the breeding grounds, or any flyway area between the breeding grounds and your hunting grounds, contain accessible waterfowl food, ice-free water, and relatively mild night temperatures, you should be pleasantly surprised by any birds that do arrive.  Especially in the Atlantic Flyway.  This frustrating and recurring phenomenon seems to be happening almost annually, and is very interesting to me as a biologist, and very frustrating to me as a hunter.

It leads me to three questions that I don't have the answers for yet:

1.  This is clearly a climatologic pattern that is impacting our 100-year old knowledge of migration dates.  Is it part of a short (5-10 years), medium (10-50 years), or long term climatic shift?

2. Assuming that any of those are true, what are wildlife managers to do with hunting season dates?  Earlier dates are becoming fruitless for migratory birds (although local birds are often around in ample numbers to fill up a few straps).  Yet, later season end dates (February and beyond) would be very likely to impact the sensitive spring migration.   For many species in many states, bag limits are becoming ridiculously liberal...and few hunters in the Atlantic Flyway can fill a bag limit consistently throughout the season.  25 snow geese? 6, 7, 8 ducks per day?  16 doves?  Many hunters have a spot they can go once or twice a season and achieve this kind of harvest - but not with any regularity.

3.  While the bulk of Atlantic Flyway birds are produced in the Great Lakes region and eastern Canadian provinces, not all of them are.  Pintails largely arrive from the prairies.   Scaup largely hail from the Boreal Forest in western Canada.  Weather that forces those species to migrate south and east may never even touch  the Mississippi/Central flyways or the Atlantic Flyways.  In short - will we start to see a different composition of wintering waterfowl in the AF? Are we already?  

As the Atlantic Flyway harvest numbers come in for the 2011-2012 season, we'll be taking a more detailed look at all of this.   Are land management practices, long thought to be strong drivers of waterfowl migration, being supplanted by climatic trends as the primary force in predicting seasonal bird movement?  We'll also take a look at the stunning 2009 report by Audubon that says, at least for waterfowl, "yes."

Plan on joining us for it!


Map Monkey said...

Very interesting, Swmapy! Yet another impact of global climate change, and IMHO, it is unlikely to be a short cycle thing. You may have to move up to "Yankee-land" to do any duck hunting next year!

e.m.b. said...

Great post...interesting and thorough. I'm bookmarking it for future reference, as well.

prpark said...

Intreresting post combining first hand knowledge with emprirical research...I was out yesterday and even the "eat at Joe's" sign didn't work. All things being equal, I was hoping that the moonless night the night before and the dropping barometer would trigger some feeding in the field. No luck, so worked on my calling..PRPark

Doc Outlaw said...

Excellent post!

It's a contentious question whether this is a short, medium, or long term pattern, but it is clearly occurring and it doesn't appear to be taken into account by wildlife managers.

There seems to be growing evidence that wildlife managers are out of sync with larger scale climate patterns. Waterfowl seasons, every year, begin roughly the same time. Ironic that shortly before the first duck split opened, DU and many state wildlife managers were predicting a record season for waterfowl, based solely on the population numbers and seeminly ignoring the climate's impact on the migratory behavior.

The adaptive management approach is applied to managing waterfowl. While I'm not intimately familiar with the process, most of what I've found on it suggest that harvest decisions are indexed to population size, habitat conditions, and the relative belief in alternative models of the degree of density dependence in survival and recruitment. It doesn't appear that weather patterns are taken into account. Wildlife managers have two potential levers to manage the system: season dates and bag limits, but they don't seem to make full or effective use of the season dates, which begin and end virtually the same time every year. It doesn't matter if the bag limit for ducks is 1 or 200 if the ducks aren't here during hunting season.

Perhaps things call for a reevaluation of management methods.

Steve Kline said...

Thirty years ago, the lowlands of Eastern North Carolina had a huntable population of migratory Canadas; now, so few Candas make the trip south to the Tarheel State that goose hunting participation has fallen off to an afterthought. This is reflective of a climactic pattern, but while we stand around bickering about whether it is long term or short term, it will be beyond the point of no return. Rejiggering hunting seasons is a response to the symptom, we need a cure for the disease. We can start the season in Mid-January, but the bottom line is that the window of opportunity is closing. On the Eastern Shore, local economies cannot afford to lose waterfowl hunting.

Passinthru Outdoors said...

Excellent post. 3 mornings of hunting in Northeast CT produce a sighting of 12 mallards and 2 geese. YIKES! Our north zone season ends next week and we haven't even see any real migration of birds our way. oh well. Should get some good shots with the camera soon though.

Thanks for sharing.