In my yard about a mile east of the CSU campus in Fort Collins (Larimer), I had
both a Swainson's Thrush and a young male Rose-breasted Grosbeak today.
Evidence that birds are still on the move.
A major activity that Norm Lewis alluded to in Lakewood the other day that I am
also seeing in Fort Collins is feeding of birds of several species on the
larvae of the Elm Leafmining Sawfly (Kaliofenusa ulmi). Sawflies are actually
non-stinging wasps. The adults of the Elm Leafmining Sawfly are blue-black and
about the size of a house fly, maybe a tad slimmer. They were commonly seen on
the leaves of elm a few weeks to a month ago. They lay eggs on the expanded
elm leaves and their larvae tunnel between the upper and lower layers,
eventually forming a big brown blotch called a "mine". When the larvae are
done feeding and as big as they'll get, they chew out of the mines and drop to
the ground for pupation in the soil. Those that are successful in completing
their development will emerge next late spring as blue-black adults. At this
time of year, zillions of larvae drop from heavily infested elms and are a
major source of food for House Sparrows, American Robins, Common Grackles,
European Starlings, and probably many other species. The characteristic
feeding pattern involves running around plucking at the ground like a chicken.
The larvae are but a few millimeters long and pale yellow. You can't see them
unless you lie on your stomach on a sidewalk or grass-free patch of earth under
an elm to the point of drawing extreme suspicion from your relatives and
neighbors.
I suspect both the Hermit Thrush and the Rose-breasted Grosbeak were eating
these today, the thrush going after larvae on the ground, the grosbeak munching
mined areas of leaves that still had larvae within them.
Dave Leatherman
Fort Collins
--
You received this message because you are subscribed to the Google Groups
"Colorado Birds" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/cobirds/SNT139-W556A13831AC85782EFF065C19B0%40phx.gbl?hl=en-US.
For more options, visit https://groups.google.com/groups/opt_out.
