Bob,

You raise an interesting point. Your posting led me to remember a few
particularly robin-rich winters in central Florida when I worked at a
research station there about 10 years ago. During some winters robins
numbering in the thousands flocked to palmetto flatwoods to feed on
palmetto berries. These berries are about the size of a big blueberry or
a small wild grape. The palmettos grow dense and close to the ground, so
the robins "disappear" in the foliage when they feed on the berries.
When driving through the flatwoods, we flushed robins up in clouds that
rivaled flocks of starlings on Ohio farmlands in November. So I guess at
least some robins go fruity during the winter, even when the weather is
mild.

Interestingly, the guts of many songbird species that shift from a
spring/summer insect diet to a fall/winter fruit diet actually change
anatomically and physiologically such that they become more efficient at
processing fruit in the fall. Perhaps this change, in response to
seasonal patterns that are consistent over evolutionary time, constrains
their diet even when worms and such may be available. Another factor may
be that robins, especially females, eat protein rich diets beginning in
early spring to fuel the production of eggs (and continue this diet
while they are caring for hungry growing offspring), and return to a
protein-poor but energy-rich fruit-based diet when they are free of the
demands of growing offspring but still need to stay warm.

Lots of interesting questions pertaining to plain old robins!

Keith Tarvin
Oberlin

----- Original Message -----
From: "Barrett,Robert P" <[log in to unmask]>
Date: Thursday, February 8, 2007 9:47 pm
Subject: Re: [Ohio-birds] Robins in Winter
To: [log in to unmask]

> -----Original Message-----
> From: Ohio birds on behalf of TUCKER, Casey
> Sent: Thu 2/8/07 5:22 PM
> To: [log in to unmask]
> Subject: [Ohio-birds] Robins in Winter
>
> Typically, a
> resident male will try to last through the winter and defend one of
> these bushes from other over-wintering frugivores like mockingbirds
> andRobins 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.
>
> ?????????
>
> I understood everything up to the return of the females in spring.
> Would a migratory female just back from the sunny southlands have
> any interest in the remaining berries on an ornamental shrub?  Or
> would she be looking for earthworms, which she had presumably been
> eating all winter in a place where the ground does not freeze?  Or
> do robins eat berries in the winter throughout the continent?  Is
> the dietary switch from worms to berries triggered by their
> inability to catch worms in frozen ground, by minimum temperatures
> staying below freezing for some length of time, by daylength, by
> the chemicals (alcohol?) in fermented and/or frozen berries making
> them more attractive than before, or by some other environmental
> change?  Trying to think like a bird, I had always figured robins
> ate worms for as long as they could, and then switched reluctantly
> to berries out of desperation, but this discussion has started me
> wondering.
> Bob Barrett
> Fairlawn, Summit County
>
>
>
>
>
>
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