About Crossbill Bills

139 Notes About Crossbill Bills John Schmelefske 2001 could certainly be described as on 28 October 2001. By 2 the year of the crossbill in areas of November, there was a small flock Ontario south of the Canadian of six or seven birds hanging Shield. The first nest ofWhite-winged around the feeders. This provided Crossbill (Loxia leucoptera) in the me with a great opportunity to test Greater Toronto Area was discov out my new digital camera. ered in the Palgrave Conservation The feeders I use are clear plas Area in February of 2001 (Coady tic tubes with tiny teardrop-shaped 2001). In the fall of 2001, as predicted holes for access to the seeds. I by many observers in the north, the remember many years ago when I poor cone crop on the Canadian bought my first niger feeder, I ini Shield resulted in a large movement tially thought I had gotten a faulty of finches southward. On my own unit because the holes where so property, approximately 5 km south small it did not seem possible that of Alliston, Ontario, from September the birds could get the seeds out. through November, I observed Of course, it proved to be no prob Purple Finches (Carpodacus pur lem for finches. This time around I pureus), Evening Grosbeaks wondered whether their crossed (Coccothraustes vespertinus), Pine bills would actually make it harder Grosbeaks (Pinicola enucleator), for crossbills to feed from a niger Pine Siskins (Carduelis pinus),White feeder. I soon realized that cross winged Crossbills and Common bills could use their tongues very Redpolls (Carduelis flammea) at var effectively to manipulate seeds. ious times, along with the usual They would stick their upper American Golfinches (Carduelis tris mandible in the feeder and leave tis) and House Finches (Carpodacus the lower mandible pointing to the mexicanus). side. Then they would use their Crossbills have always gotten a tongue to wedge a seed against the lot of attention for their amazing upper mandible and slide it out of bill adaptation, and rightly so. Last the feeder (see Figure 1). Clearly, fall was the first time I had ever had the unusual beak is only one of White-winged Crossbills coming to their assets. It makes sense that my feeder. The first arrivals were while the bill would be helpful in two juveniles, which I first noticed prying cones open, they would need VOLUME 20 NUMBER 3 140 a dexterous tongue to finish the job. resources are low and crossbills Unfortunately, one of my start corning to feeders, as they did White-winged Crossbill visitors had in 2001. My impression was that a terminal encounter with our slid these marks were not deep enough ing doors. The autopsy revealed to cause serious damage, but that curious markings on the upper over a whole winter it might be a mandible of the beak (Figure 2). I problem. It may be that, because of wondered if these abrasions might the bill shape, crossbills have to do have been etched into the bill by more maneuvering to access niger the edges of the openings in the feeders and consequently are more bird feeder. I had bought new niger susceptible to bill damage. feeders that year and thought that perhaps the sharp edges of the plas Discussion tic were hard enough to cause this I have no way of knowing with any kind of damage. The scratches were certainty whether the bill markings superficial, but potentially this were actually made by the feeder could have a significant impact on openings. I did not notice the marks wintering birds during years when on the beak until I looked at the Figure 1: White-winged Crossbill removing seeds from niger feeder. Photo by John Schmelefske. o TARIO BIRDS DECEMBER 2002 141 Figure 2: Dead White-winged Crossbill with abrasions on the bill. Photo by John Schmelefske. pictures later long after tossing the Craig Benkman crossbill remains over the back fence. I went expert and author of the White over the 60 other photos that I took winged Crossbill account in The of crossbills at the feeders, and saw Birds of North America (Benkman no obvious similar markings but 1992) kindly examined my photo this may be because the pictures graph and considered that the con were taken at too great a distance clusions concerning wear on the bill to pick up such details. Are there seem reasonable although I doubt other possible explanations for that such wear even over a winter these marks? Well, I doubt whether would prove harmful to the bird" conifer cones would have the (Craig Benkman, pers. comm.). degree of hardness necessary to Thinking about crossbills got cause such damage. I considered me thinking about crossed bills. whether the marks might have One thing I noticed from my pic resulted from the impact on the tures was that some crossed bills go window but they look like etchings top-to-the-Ieft and bottom-to-the on the surface not fractures due to right while others go top-to-the impact. right and bottom-to-the-Ieft. I won- VOLUME 20 UMBER 3 142 dered whether there is a theory as lower mandible crossing to the left) to why they go either way and in that species (Benkman 1996). whether the ratio of each alterna Even more intriguing is whether tive had been measured? one variant spins the cones one way A search of the crossbill litera when it eats and the other spins ture revealed that the lower them the opposite way? Craig mandible of the North American Benkman (pers. comm.) stated that subspecies of the White-winged this does not appear to happen, but Crossbill (L. l. leucoptera) crosses that he had not systematically tested to the right approximately three it. Does one approach cones from times more often than to the left the left, and the other from the (Benkman 1988), while the lower right? mandible of the Red Crossbill (L. According to Bent (1968), curvirostra) "crosses to right as based on studies of captive Red often as to left" (Adkisson 1996). Crossbills by Tordoff (1954): "Birds Why the difference? Benkman are either right-handed or left (1996) theorized that the 1:1 bill handed in opening cones, according type ratio in Red Crossbills "results to which way the mandibles are from negative frequency-depend crossed. In feeding, the birds carry ent selection favouring the rarer pine cones with their bills to a morpho A crossbill always orients perch, hold the cones with their toward closed conifer cones so that feet, and insert the tips of the open its lower mandible is directed mandibles. With the long axis of the towards the cone axis (Benkman bird's head approximately at right 1987). Thus, only part of the cone angles to the long axis of the cone, can be reached easily when cross the tip of the lower mandible press bills have few perch sites and the es towards the central axis of the cone cannot be removed from the cone and raises a scale against the branch or otherwise turned around. essentially stationary tip of the Since crossbills may visit cones upper mandible. The tongue then which have previously been foraged probes and removes the seeds." on by other individuals, an equal Perhaps even more fascinating frequency of left-to-right mandible is the following account of Red crossings may minimize overlap in Crossbill roosting behaviour in Bent the use of cones and enhance forag (1968), again based on research by ing efficiency." In contrast, our Tordoff (1954): "Before going to White-winged Crossbills "forage on sleep birds extend and retract their cones that are easily twisted and tongues, three to five times a sec removed from branches", and since ond, for as many seconds. After a they manipulate the cones for effi pause, they repeat the process. The cient foraging, there is no selective tongue may project on either side of advantage for the rarer morph (i.e., the mandibles, and it extends well ONTARIO BIRDS DECEMBER 2002 143 beyond the tips. Sizable clusters of Clearly, the crossbill is a bird white frothy bubbles appear at the worthy of observation. In many ways ends of the bills. These clusters soon they remind me of parrots, with their break, leaving the mandibles wet highly evolved and dexterous bill and and shining. Coincident with the tongue. Behaviourally, the way they tongue action the birds open and forage so gregariously in groups, close their bills, but at a slower rate. hanging upside down and stretching Also, they close the bill in the to reach food, makes me think of "wrong" direction, resulting in a them as the boreal parrot. peculiar appearance because the mouth will not close evenly. It is Acknowledgements possible that this procedure brings I would like to thank Craig Benkman about a wearing down of the non for his helpful comments on an earli occluding edges of the bill by abra er draft, and RonTozer for assistance sion, with the moisture acting like with the literature. water on a whetstone." Literature Cited Adkisson, C S. 1996. Red Crossbill (Loxia Benkman, C.W. 1996. Are the ratios of bill curvirostra). In The Birds of North crossing morphs in crossbills the result of America, No. 256 (A. Poole and F. Gill, edi frequency-dependent selection? Evolu tors). Academy of Natural Sciences, tionary Ecology 10: 119-126. Philadelphia, and American Ornitholo Bent, A.C. 1968. Bent's Crossbill (Loxia gists's Union, Washington, ne. curvirostra benti). Pp. 520-524 in Life Benkman, C.W. 1987. Crossbill foraging Histories of North American Cardinals, behavior, bill structure, and patterns of Grosbeaks, Buntings, Towhees, Finches, food profitability.

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