The same thing would happen this time of year at our previous home in south
Eugene, only it wasn’t chokecherry but Portugese Laurel. (Old, well-established
bushes that were there when we moved there over 20 years ago. They are not
native so I don’t recommend them.). For days the fruits looked ripe but were
untouched by the birds and suddenly, one day, many Cedar Waxwings and Robins
would show up and devour the berries over the next few days. Why they suddenly
come is an interesting story.
When the fruits are ready to have their seeds dispersed, a change occurs that
we can’t see. For the plant, the strategy is to attract birds who will eat the
fruits whole and disperse the seeds in their droppings. To attract birds at
just the right time the seed coat changes and suddenly begins to reflect
ultraviolet light. We see no change because we don’t see UV light but birds see
it well and this is their signal that the fruits are ready to eat. Robins are
large enough that they can usually crush the fruit in their mouth and squeeze
out the juicy parts they desire. They swallow the seeds whole as they are
embedded in the fleshy part of the fruit. Waxwings have a different method.
Many of the fruits are just a bit too large for the waxwing to crush in its
mouth. The tongue helps force the fruit to the back of the mouth where it is
swallowed whole. Once swallowed, the rear portion of the stomach, the gizzard,
can squeeze the fruit and remove the fruit’s heavy cuticle leaving the inner
portions to be digested, which is waxy and can’t be digested. It’s much like
you squeezing a slip-skin grape. You squeeze it into your mouth and you get the
juicy inner part leaving the skin behind. For the birds, these skins are pushed
to one side of the stomach and compacted into a pellet. At some point the
pellet becomes large enough to cause the stomach to regurgitate and discard the
pellet. If you’re not aware of it, most birds do cast pellets, not just owls
and raptors. Indigestible parts, like insect wings and exoskeletons often are
part of these pellets. They just aren’t as obvious and well-formed as owl
pellets so we usually don’t see them.
Dan Gleason
Dan Gleason
Owner, Wild Birds Unlimited of Eugene
Ornithology Instructor, retired, University of Oregon
dan-gleason@xxxxxxxxxxx
On Oct 5, 2022, at 8:54 PM, Paul T. Sullivan <paultsullivan@xxxxxxxxxxxx>
wrote:
It's that time again. My chokecherry bush if full of fruit and the Cedar
Waxwings and Robins are on the job.
Paul Sullivan
McMinnville
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<C waxwing on chokecherries 10-5-2022.jpg>
