[Tweeters] White winged crossbills observation and questions...
khanhbatran at hotmail.com
Thu Feb 28 19:08:34 PST 2008
Forgive me for the discursiveness and grammatical errors of this post. I am not a very good writer. Anyhow, I hope to learn something new from other birders on this forum.
So far, It has been amazing winter for the engimatic,elusive but beautiful White winged crossbills. Birds have been spotted in several locations and habitat since July 2007 to present. I am still new to Tweeters but after going through 8 year of archives and only finding a few handful of sited reports (realizing some sighting are not reported), this may be the best year to study them. The numbers and locations of sitings have been great.
It not surprising why they are hard to find; their varied feeding habits and breeding requirement are partly contributed. Secondly, most of their prime habitat is often unaccessible except for the late spring and early fall. Even so, these areas are often unbirded and require extensive effort in travel and hiking.
Since little is known about these irruptive, erratic visitors in WA, I had a few observations and questions. With everyone's observations, maybe we can gain a better understanding of these beautiful birds. It has been fun reading everyones posts and excitment!
In the WA guide, it is noted that breeding is suspected but not confirmed. However, Stefan S., Micheal F. and Ted. K. have seen the birds picking up nesting material at Steven's Pass.
I am no expert, but have been extremely lucky to stumble upon many this past 6 months near Bunchgrass Meadows, Mt.Adams, and the Okanogan Highlands.
1) Birds in WA have been seen or feeding on cones in Western larches, Englemann spruce, Mountain Hemlock, Silver fir. Joseph Higbee and I photographed immature females at Hart's Pass in Western larches while many observers at Steven's Pass have seen them in the latter habitat. Birds seen and heard last summer at Togo Mt and Bunchgrass were in a mixture of hemlocks and Englemann spruce.
This variety of food source probably explains their normadic tendencies moving from one place to another as one food source is depleted. One bird is known to consume more than 3000 seed per day. Imagine a flock on 30 or more birds in a small area with an average cone supply.
The Clement, Harris and Davis Finches and Sparrow book mentions the following: WW crossbills feed on a variety of food items compared to other crossbills. extracting seeds from larches, cedars, spruces and hemlock. It also takes berries, spiders and insects and their larvae.
Also birds frequently mix with flocks of Red crossbills, redpolls, siskins, and evening and pine grosbeaks. Flocks up to 50-300 is not uncommon. This phenomenon is now being observed at Steven's Pass. In December, I had up to three small flocks in the Okanogan sometimes mixed in with redpolls, crossbills, and siskins. Steve Nord and I had some mixed in with pine siskins at Hart's Pass.
I have seen on two occasions in Northern BC and the Wallowas (Lostine area) birds feeding on scat or horse dung. Is this a source of protein and calcium for their strong bills to allow them to pulverized the hard cones and seeds??
2) If they birds are breeding at Steven's Pass they are now showing signs of pairing off.
Gene Hunn suspected that they were breeding at Steven's Pass this winter and saw a few immature birds. According to Newton, there is a 40 day interval between the start of egg laying and fledgling of young. So some of the birds must have started in late December or Janruary. It makes you wonder how determined and devoted the parent birds are if this were true. It would require alot of work to chisel through the ice, snow laded cones.
With this warm weather pattern the past several weeks, the cones and seeds are more exposed for the birds. As a result, they are starting to show signs of singing and breeding.
I also noted, I had the most success and bird activity when the cones were exposed rather than completely covered with snow. I saw most of my sightings from 8-10 AM in the morning at various locations in NC and NE Washington.
According to a study done by Samson in 1976, the WW crossbills have a breeding system like the Cassin's finches. Specific similarities include:
all adult males are mated and paired
all females are mated
a population unmated first year male exists
adult males cease singing when paired while first year males continue to sing
the males territory revolves around the hen
This style of breeding seems adaptive for these highly nomadic, irruptive WW crossbills which dependable cone crop.
The isolated breeding population in Utah relied on the heavily produced cones from Engelmann spruce, it was the best cone year in 30 years where some trees beared more than 4000 cones. So this opens a few questions....
A study done on an Alaska population observed the birds breeding from May to July and then Feburary to April (which is consistent with current activity seen at Steven's Pass). I observed birds singing (several males in courtship display) in July at Bunchgrass Meadows; late January in Molson, WA near Nine Mile Rd (perched male).
White winged are capable of breeding at all times of the year except when molting in the fall. This may be photoinduced increase in prolactin secretion is a factor that induces molt. The birds may not breed when they molt because of increased metabolic demands for feather formation and maintenance of basal metabolism at a time of eyar when ambient temperatures fall well below freezing. Alternatively or in addition, the birds may become photorefractory. (Deviche and Sharp 2001)
Will the birds in Steven's Pass stay and breed?? Were the bird originally from the North and forced southward because of a low cone crop year? How will they improvise and adapt their breeding cycle?
Perhaps earlier in the year when Matt Dufort and Gene Hunn first observed them, they had just arrived and now realized Steven's Pass has sufficient food for them to breed and now they are pairing off?
So how does the molting coincide with the available cone supply or crop? When it warms up and there is more light, do the cones open up or more seeds are produce? I don't know my fir, spruce, and cone biology? Can someone enlighten me??
What ever the case, I hope the birds will stay and breed encouraging more birder to get out and observe. It has been a fun winter. I can't wait for spring!!
Khanh Tran (Portland, Oregon)
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