Hi All,

 

Bill Whan's comments regarding Robin observations and occurrences were
right on the money.  I just want to add a little more information that
might also help explain recent observations of large groups of Robins in
the state.

 

One of the things to consider is that up until recently much of the
winter has been relatively mild with little to no snowfall through much
of the state.  The recent onset of snow and cold (in some cases subzero
temps.) have covered many wild food sources.  This may be causing Robins
to congregate in more urban and suburban areas to take advantage of the
urban heat island effect that these areas have; typically being several
degrees warmer than surrounding rural areas.  As a result it may also be
giving the impression that there are suddenly a lot more Robins around.

 

Bill's observation that birds don't eat English Ivy fruits until after a
good freeze is true for many kinds of winter berries, both native and
ornamental.  These winter fruits typically have a small amount of fat in
them, as well as a little carbohydrate.  Additionally, many winter
fruits are protected by secondary compounds that make them distasteful
and, in some cases, toxic to many kinds of animals.  For some fruits
it's thought that freezing helps to lessen the content of the secondary
compounds and makes it easier for birds to eat them.  The recent freeze
is probably allowing birds to exploit many of these fruits now.  

 

Some fruits, like those on the American Cranberrybush (Viburnum opulus)
are produced in mid to late fall but aren't eaten until much later.
During the winter the sugar concentration in the berry seems to increase
which may be related to freezing, but American Cranberrybush fruits also
contain a secondary compound called chlorogenic acid.  When birds, like
Cedar Waxwings, eat berries from American Cranberrybush it lowers their
pH and causes their bodies to become acidic (which can be problematic-if
you like to cook, think about how Ceviche is made).  To counter the
effect of the acid birds must eat something that will neutralize the
acidity.  What they turn to are catkins from Cottonwoods.  The catkins
contain protein which is broken down during digestion into ammonium and
the ammonium neutralizes the acid.  As a result some winter berries will
persist into spring until their dietary complement will become
available.

 

As Bill mentioned many of the Robins that are here currently may be
moving southward, and part of the reason we may have so many now is that
we have had an influx of Robins from further north inter-mixing with
some of our resident Robins that, up to now, have not seen the need to
head southward.  As the number of Robins begins to decline keep an eye
on any berry bushes that have retained their berries.  Typically, a
resident male will try to last through the winter and defend one of
these bushes from other over-wintering frugivores like mockingbirds and
Robins from further north.  It's thought that these males are trying to
protect a food source for their own use during the winter, but also a
source of food that may attract females when they return during the
spring.  This, in turn, may help the male find a mate.

 

 

 

Thanks,

 

Casey

 

Casey Tucker

Education Specialist

Audubon Ohio

692 N. High St., Suite 303

Columbus, OH 43215

614-224-3303 (phone)

614-224-3305 (fax)

[log in to unmask]

www.audubonohio.org

 

 


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