Scott, David, et al,
Re crossbills at lower elevations, and cone crops in general, I would say the
following:
Conifers produce cone crops at fairly irregular intervals, with what nursery
people refer to as "bumper" crops occurring only every 3-5 years for most
species of coniferous tree (in Colorado that would be pines, spruces, true
firs, and Douglas-fir). Heavy cone crops can be triggered by both moisture
(i.e. "good" growing conditions) and stress (i.e. "bad" growing conditions).
If the stress is bad enough, and the plant has a physiological sense it might
die, available energy can be, and often is, put into cone production as the
best means of sustaining the species. Last winter and the months hence have
generally had good moisture over wide areas of the Colorado mountains, so, as
David suggests, cone production this year is mostly in response to good
conditions.
Most conifer cones take one to two years to mature and produce viable seeds.
Cone production starts in late spring after pollination of female cones (called
"strobili") by pollen from male strobili. The resulting seed-bearing cones
develop during the summer, and the future "inventory" available for
exploitation the following winter (or the winter after that) becomes evident
about this time of year. Thus, crossbills which are highly dependant on such a
widely scattered, both geographically and temporally, resource as cones, need
to engage in extensive scouting. Type 2 Red Crossbills dependent on ponderosa
pine apparently have the ability to differentiate between 1-year old ("unripe")
and 2-year old ("ripe") cones during scouting. I am not sure if this is done
visually while on the wing (conifer cones are concentrated in tree tops AND the
color of these two ages of cones ARE different), or if they have to stop and
examine things/sample things more closely. Regardless of what exactly it
entails, in my experience, much scouting occurs from mid-July thru the onset of
winter (November-early December). How scouts convey information to the general
population of crossbills is also a mystery, at least to me. But if you've ever
watched a group of crossbills quietly feeding atop a conifer, and then heard
one of them begin to call ("I'm having a tougher and tougher time over here
finding seeds easily, I say we move on", or, "Is it just me, or do you guys
feel Merlin eyes beating down on you?", or whatever it is they say), followed
by a crescendo of the others calling in agreement, followed by them all flying
off, they are obviously able to vocally convey information.
Whether we see conspicuous numbers of crossbills in the foothills or out on the
plains probably depends a lot on the situation in the mountains. If cone crops
are good everywhere in the mountains, not much scouting elsewhere will be
necessary. But I would wager, diligent observation would result in at least a
few sightings in almost every county on the eastern plains, and that if they
occur, July-October would be the most likely time to see out-of-the-mountain
wandering crossbills (and corvids, which also eat a lot of conifer seeds).
Dave Leatherman
Fort Collins
Date: Wed, 30 Jul 2014 13:29:08 -0700
From: [email protected]
To: [email protected]
Subject: [cobirds] Re: Boulder County, July 30
Scott:
I haven't encountered any in town yet but did find some low down in Skunk
Canyon (southwest Boulder) yesterday. In general, Red Crossbills are seemingly
everywhere in the northern Colorado mountains this summer (based on my own
observations plus the number of red dots -- recent reports -- on ebird). Has
the deep soil moisture built up during the previous 10 months resulted in a
good cone crop?
David DowellLongmont, CO
On Wednesday, July 30, 2014 12:54:57 PM UTC-6, Scott Baron wrote:
Also, has anyone had Red Crossbills in areas outside the mountains recently? I
think I heard them as flyovers a few times this Monday and Tuesday in the city
of Boulder.
Scott Baron
Loveland, Colo.
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