Just a heads-up that hackberry trees from now until the first hard frosts would
be worth checking closely for migrant passerines. During yesterday's Denver
Audubon field trip to Grandview Cemetery in Fort Collins, we observed 8 species
of birds in one Northern Hackberry tree (house finches, black-capped
chickadees, downy woodpecker, red-breasted nuthatch, Wilson's warbler,
ruby-crowned kinglet, western wood-pewee, and dark-eyed junco). As has been
noted in earlier posts about hackberry psyllids, there are two common species
of psyllids forming leaf galls in ornamental hackberries along the Front Range:
the so-called nipplegall-maker and the blistergall-maker. Some birds eat both
types of gall-makers while they are still in the galls by either biting off the
nipplegalls and consuming both the gall and maker within, or pecking right thru
the blisters. House Finches are the primary species I've seen nipping the
nipplegalls off leaves, with chickadee spp. being the primary species going
after blistergall psyllids while still inside the leaves. Many, many species
of birds eat both species of psyllids as adults once they emerge from the two
types of galls. The adults at this time of year are emerging to find their
way into overwintering sites in the bark of hackberry and nearby trees
(especially spruce). Six of the 8 species of birds we saw foraging in
hackberry yesterday were types that usually favor free-living adults. I was
unaware emergence of either species of adult psyllid had commenced, but the
activities of the warblers, a kinglet, and chipping sparrow prompted further
examination. Sure enough, tiny, very pale, freshly-emerged adult blistergall
psyllids were, indeed, out and about (easily seen on the polished surface of a
black headstone). Based on examination of a small sample size of nipplegalls,
it would appear the emergence of adults of this species is a couple weeks away.
In summary, and assuming we don't have 10 feet of snow or a -50 degree freeze
in the near future, it looks like hackberries showing infestations of these
gall-making psyllids should be attractive to passerine migrants for a matter of
weeks going forward (maybe well into October).
Dave Leatherman
Fort Collins
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