There is a phenomenon on-going involving evening primrose (a white-flowered
species of Oencantha), the white-lined sphinx moth (Hylea lineata), and birds.
Caterpillars of the moth are gorging on the abundant plant, which, in response
to much-needed rains, blanketed the northern prairies of Larimer and Weld
Counties with blooms in this late spring. The caterpillars in spots have
out-stripped the sparse leaves of this plant and are wandering in search of
more leaves to complete their development. If they make it to adulthood, they
turn into what many call a "hummingbird moth", familiar to most of us as they
hover about ornamental flowers at dusk (they are boldly marked with dark brown
and white, with mostly pink hindwings, long proboscis, ghostlike).
Technically, other sphinx moths are more properly called hummingbird moths, but
this post isn't technical. Above I said, "If they make it..." because birds,
and I suspect other potential predators, make the completion of their
metamorphosis less than a sure thing. So far, during this spate of hundreds
(thousands?) of caterpillars wandering across roads in Larimer and Weld, birds
of many species are cashing in on the bounty. To date I have seen House
Sparrow, Lark Buntings, Horned Larks, Western Meadowlarks, and McCown's
Longspurs involved. I have a good photo of a female McCown's Longspur subduing
a caterpillar taken on 6/30, if anyone would want to see it. I suspect this
will be subject of "The Hungry Bird" in "Colorado Birds" at some point, so you
will see this photo again.
One good place to see the caterpillars and bird response, including McCown's
Longspurs, is CR5 north of Buckeye Road (the exit on I-25 near the WY line one
would take for Hamilton Reservoir near the Rawhide Power Plant). Go west on
Buckeye Road from I-25, cross the RR tracks, and take the first county road
north. Note that normally one could hit CR29 at the north terminus of CR5 and
go east to I-25 at the Carr Exit, but the other day there was bridge out which
prevents this (was out on 6/30, may be fixed now).
Also, longspurs of any type are somewhat hard to find this year on the northern
prairie. While wandering aimlessly on 6/30, I had good numbers of McCown's of
all sexes and ages on Weld CR120 between 55 and 67. I have yet to find a
Chestnut-collared, but surely they are out there, too, albeit fairly locally.
I note where Gary Lefko reported them on a Pawnee BBS without details.
There are 4 female type Barrow's Goldeneyes on Echo Lake (Clear Creek) as of
6/26, first reported by John Breitsch on 6/24. A dusky Fox Sparrow was singing
about a half mile west of the Guanella Pass Summit (Clear Creek) on 6/26. Gray
Jays and Clark's Nutcrackers were east of Echo Lake at the campground on 6/26.
We did not find Pine Grosbeaks but Doug Kibbe, who we ran into, said he had
seen two in the campground on 6/26. From public parking for the trailhead near
the campground host campsite looking north, we had 3 Band-tailed Pigeons either
flying over or perched in distant dead conifers. Lots of Red Crossbills on
Squaw Pass Road (SR103) between Echo Lake and Squaw Pass itself (Clear Creek).
Also Gray Jays in the picnic areas along this road.
Dave Leatherman
Fort Collins
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