[CT Birds] Ducks again

[David.F.Provencher at dom.com]

I would have to say I haven't seen any evidence, nor read any accounts, of
waterfowl actually retreating southward during the northbound migration in
response to meeting harsh conditions. Greg mentioned their ability to find
whatever open water is available. My experience has been to find truly
remarkable concentrations of individuals and species in small areas of open
water when migrants run into harsh/frozen conditions. Or when sudden cold
snaps close up many bodies of water. A number of years ago just such a cold
snap occurred here at the beginning of the migratory period and Smith's
Cove on the Thames in Waterford was full of ducks, grebes, and geese all
squeezed into what available open water was available. Waterfowl will push
further south during winter in response to cold weather closing up habitat
but during the Spring migration their behavior is strongly driven by
breeding instinct and chemistry changes. The energy used during migration
is also a consideration. Many species rely on fat reserves to migrate at
all and then successfully breed. There would be considerable reserves used
to back-track on migration and any birds that did so would risk failing to
successfully breed at all that year. The fact that migration causes such a
heavy toll on birds each year shows the power of the drive to push north to
breed.

I believe what happens to early migrants that encounter unexpectedly harsh
conditions is that some will succeed in finding enough open habitat to get
by as Greg pointed out, and some will perish. The mortality rate will
depend open the severity and length of the bad weather and unfavorable
conditions. During Fall migration, young birds and females of many species
migrate farther south than males. These females will tend to make out
better in Spring regards to bad conditions farther north because they tend
to migrate after the males, that is as long as the harsh conditions aren't
protracted. The young males however face the toughest challenge. They have
to travel the farthest and then try and carve out a breeding territory for
the first time. Thus their rate of mortality and chance of breeding failure
will likely be statistically the highest. Historical bird populations were
large enough (for the most part) to absorb years when migration mortality
was very high or large scale breeding failures occurred. The ability of
existing waterfowl populations to deal with such events, and whatever
consequences climate change will bring, depends upon many factors. One
thing is certain, we are likely entering a period of great changes.

Dave



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