Dave, thanks for confirming my identification of leafminer and from the genus Phyllonorycter and family Gracillariidae.
The tiny moths are taking flight and when I was at Florence River Park today I saw a several dozen of them. If birders go out in the next few days, these moths appear to float when there is no breeze.
I did not see any of the birds pursuing these moths but I think it is more sense for them to eat the pupae than to expend the larger amount of energy chasing these tiny moths. More later on this and some other food that the birds are consuming.
SeEtta Moss
Canon City
Blogging for Birds and Blooms magazine @ http://birdsandbloomsblog.com/author/seetta-moss/
Personal blog @ BirdsAndNature.blogspot.com
On Tue, Sep 25, 2012 at 5:58 PM, DAVID A LEATHERMAN <daleatherman@msn.com> wrote:
-- SeEtta et al,
This is very interesting. I collecting some of these, or something very similar, from Plains Cottonwood about a week ago at Roselawn Cemetery in Fort Collins. The makers of these pale circles are emerging in a container in my "lab" (aka kitchen). Yes, they are leafminers. Many different groups of insects, from flies to beetles to moths, have representatives with the leafmining habit. The causal organisms in the case you documented are tiny moths, very likely in the genus Phyllonorycter, family Gracillariidae. The larvae tunnel around between the top and lower layers of the leaf, with the fed-upon area usually appearing as a discolored blotch or meandering trail (depending on the species of miner and its particular style). When the larvae are done feeding, they pupate (in this case within the mine), and emerge (in this species, at this time of year). Tiny, pale moths emerged today in my container from mined leaves picked 4 days ago. I suspect you are correct in your guess the birds are after pupae (which would be detectable to them as a dark area within the pale mines). If you go back and look at these trees, my guess is for mines from which the causal moth has emerged and flown away, you will see a slender, dark pupal skin protruding from each mine, or at least a tiny hole.
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