A few weeks ago a Morning Dove out sprinted our resident Cooper’s Hawk. Unfortunately, for both birds, the dove ended the flight with a heavy thud against an unyielding window, and the hawk missed a meal. This reminded me of part III of the Acorn Woodpecker series. Remember fitness? How do the strange breeding practices of our Oak Woodland Clown assure fitness? In turn this brought to mind our sighting of Red Crossbills on a summer TMBC field walk on the side of Tehachapi Mountain.
If flying faster allows a Mourning Dove to avoid becoming a meal for a Cooper’s Hawk, the faster (more fit) individuals, if flight speed is hereditary, will produce a generation of faster individuals. Relative to others, being fast is an adaptation. So, what about Galapagos Finches, Hawaiian Honeycreepers and our Tehachapi Red Crossbills?
On the isolated Galapagos Islands are found 14 finches species (family Emberizidae) thought to have evolved from a common ancestor. Generally they are sparrow sized birds with short wings and tails. Each specie bill shape and size differs. These bills differ by feeding habits. These adaptations have produced ground, warbler and tree finches, with some being vegetarians, others became insectivors, plus ground feeding finches, and even a Woodpecker Finch. Stemming from a common ancestor, this is called adaptive radiation.
Isolated, as in the Galapagos Islands, 32 Hawaiian Honeycreepers specie (family Fringillidae) (some are now extinct) dramatically exhibit bill shapes resembling parrots, hummingbirds, finches and others. All resulting from feeding adaptations. Adaptive radiation, again, birds stemming from a common ancestor. One, the Akiapolaau, has a straight, stout lower mandible, while the upper is long and sickle shaped. Holding its beak open to keep the upper mandible out of the way, it chisels woodpecker-like with the lower mandible. The bird then uses the upper mandible to probe for insects.
Family Fringillidae, Genus Loxia, specie Red Crossbill. These birds are very well named – the males are red, and the mandibles are crossed. Although only weighing 1.3 oz, this 6-inch bird appears fat and large headed. Their long, pointed wings (11” wing span) are dark. Females are an off-yellow. Juveniles are stripped breasted, looking a bit Pine Siskin-like. Males go through an orangy to reddish plumage on their way to maturity.
TMBC members will recall the September issue of The HOOT relating our latest Tehachapi sighting of Red Crossbills. Appearing to be several families, with their crossed bills, the birds were doing a number on several heavily coned Jeffery Pines. There are left-billed and right-billed crossbills, with the distribution about even. This is probably an adaptation to variances in cone structure on any given tree. However, there is more to the bill story of this exquisite little nomad.
We were first aware of their presence by the flock’s loud chip chip (the way I hear them) calls – and thus starts the story of the unknowns about this enigmatic bird. There may be as many as nine races (sub-species), with different calls, bill size, and cone specie preference! Several races may exist in the same mixed forest without interbreeding. There is a possibility there are not just 9 races, rather, they may be nine separate species! Bill sizes vary (there are overlaps) from just under 13 millimeters to a bit over 17 millimeters. Smaller billed races seem to prefer soft, smaller coned conifers such as spruces, while larger billed birds are seen on the hard, bigger coned pines.
Since vocalizations are the best means of specie identification, Sibley, in his new bird guide, displays the nine bill sizes, relates these to the calls of the nine types, and in turn outlines the general ranges of the nine races (species?). Types 1 through 4 occur continent-wide, types 5 and 7 only in the west. Further, being dependent on varies coniferous specie cone production, this bird is highly nomadic. They go where there is sufficient food supply. A few years ago flocks were recorded in such places as Ridgecrest and the Mojave Narrows.
With changing climates, changing ecological provinces, along with changing balances in tree species and forest ages, 1000 years from now, will our bird cards list nine (or less, or more) crossbill species? All with, sans binoculars, very identifiable beaks adapted to new environments and habitats? Perhaps adaptive radiation right here in our own backyard!
Our club’s sighting in Mountain park was an excellent one. However my best view was near 9700 feet in the White Mountains along the head waters of Crooked Creek. Close at hand, flying up from drinking at creek’s edge, 27 Red Crossbills - red males and yellow females - decorated a very young ten foot Bristlecone Pine.
This appears to have been an excellent Jeffery Pine and White Fir cone season, so when you’re in the yellow pine and fir belt of our Tehachapi Mountains, with winter almost upon us, listen and look for these active, adaptive, red and yellow birds with their crossed bills.
Good birding, gone birding.
Trackback(0)
 |
TrackBack URI for this entry
Subscribe to this comment's feed
Show/hide comment form