Aug. 30, 2010
Somehow the hill we live on became a vulture roost the past two years. They would show up in the spring and stand on one of our large rocks down below the house to air their wings out. Then a pair took up residence in a flimsy treehouse my son and the Van Noord kids made when they were about 8. The treehouse — really just a flat piece of plywood — is in a buckeye tree. I suspect their nest was in a large crevice in the rock below the buckeye.
Last year I don’t think they were too successful. After they had left for the winter I found a skull and skeleton of a fledgling bird that was obviously a vulture. I suspect a squirrel I saw working its way through the oak trees toward the general direction of the nest was the culprit, although the vultures could grab a squirrel as a meal.
This year I was startled to walk by the big rock by the buckeye tree and saw a fuzzy vulture with splotches of white. It was large enough that it looked like it could fly, if not then, certainly soon.
While we enjoy watching the vultures and red tailed hawks float past our living room window, I found their walking habits not so entertaining. Trouble is the vultures would spend a lot of time walking around in their own substantial droppings and would leave white bird prints on our deck when we were not home and on the tile path through my Zen garden. I think they got on our deck to drink the cat’s water. In the process they knocked over the fan and it has acted funny ever since, being slow to get to full speed.
Raptors of California notes, however, that the vultures “squirt excreta on their legs in hot weather to promote evaporative cooling.” It’s called urohydrosis. I call it gross.
Vultures are migratory. They seem to have already disappeared. They head south along the foothills, Between September and October, according to Introduction to California Birdlife by Jules Evens and Ian Tait, 3,000 turkey vultures a day will fly over the Kern River town of Weldon near Lake Isabella and also the Tehachapi Pass. Folks down there have been counting vultures the last week of September since 1994. The two low spots in the Sierra funnel the vultures through to the Mojave River. The average estimates range from 25,000-33,000 vultures. Additionally, the bird counters have seen up to 16 raptor species at this spot, according to California Birdlife.
This migration takes place simultaneously with the Coast Range migration of raptors that is observed from the Marin Headlands. An observatory set up there in 1992 to monitor and count the migrating raptors recorded an average of 5,500 vultures, 6,597 red tailed hawks, 3,400 sharp shinned hawks, 1,900 Cooper’s hawks, 500 northern harriers, 61 white ospreys. All of these were averaged between 1992 and 2002. Less common sightings include peregrine falcons, northern goshawks, golden eagles, prairie falcons, white tailed kites and over 500 northern harriers and almost 500 American kestrels. The list goes on but does not include bald eagles.
Vultures largely live off of road kill — flattened snakes, squirrels and raccoons. They will also eat mice, ground squirrels and small insects, even pumpkins, according to Raptors of California by Hans Peeters and Pam Peeters. Their acute sense of smell will lead them to even dig up a carcass.
When courting they will fly together. They don’t build nests. They just lay the eggs on the floor of a cave and incubate them for about five weeks, according to Raptors of California.
The Introduction to California Birdlife by Evens and Tait is organized by environmental region — marine, coastal, Coast Range, Central Sierra and Delta, mountains and foothills, and Great Basin. The Coast Range is further subdivided into “humid north,” Central Coast and “arid south.” It is not really a bird guide, but more a way of relating birds to their bioregions.
The book is 280 pages with 150 color illustrations and seven maps. It is printed by the University of California Press in Berkeley.
The other birds I enjoy watching are owls. We’ve had a screech owl at our house and have seen pygmy owls twice. The first time the pygmy owl was in the middle of our road in the treed area and we surprised him while driving home at night. The second time my daughter spotted one in the hollow of an oak tree near the house one morning. Good eye. It was difficult to distinguish between the bird’s color and the oak bark.
Next I plan to build some barn owl boxes and have them placed high in the trees when I have a tree service trim some of the tree branches near the house.
Raptors of California by Peeters and Peeters is strictly about daytime birds of prey, including vultures and condors. The most common raptors seen in the foothills are turkey vultures and red tailed hawks who can be seen soaring on the thermals and updrafts generated along hillsides. They can even use the thermals to hover over a likely rodent location. In the spring the red tailed hawks will do a lot of shrieking while soaring.
“To proclaim their ownership of territories, raptors vocalize and perform aerial displays, the latter serve simultaneously for drawing mates and for courtship. Red-tailed hawk pairs circling over their territories meet at the boundaries screaming what likely are obscenities at one another,” Peeters wrote.
The term “eagle eye” is more than a saying about someone who can see something the rest of us didn’t notice. “Whereas humans have only a small central area on their retina for high-definition color vision, the cones (color receptors) for all diurnal birds are spread all over the retina. For good measure they have four types of cones where we have only three kinds,” Peeters wrote.
Some raptors even can detect ultraviolet reflections of rodent urine and feces, thus giving them an advantage in finding vole rich hunting grounds.
To us a mouse at 50 yards, if we can see it that far away, will look like a brown blob. But a hawk will distinguish its eyes, ears, other details and its movement. It is not telescopic vision, just extremely acute vision with extra acute focal spots for discerning details and detecting movement.
“Like other birds, they also see faster than we do, that is, they can separate two visual images in about half the time that it takes the human eye to do so,” Peeters wrote. This enables some raptors to chase birds through forested areas like a cruise missile with topographical maps programmed into its computer.
For those who are interested in “birding” and adding to their “life list” of birds, the book lists 20 places that are key raptor viewing sites around the state.
California Raptors is a very useful guide. It begins with informative general information on raptors and then gives detailed information on each species. In the back are very good plates of each species (12 pages), including varying stages of juvenile development, so that one won’t mistake a young red-tailed hawk for a different species.
The book is 305 pages in paperback and covers 27 species, with range maps for 18. There are 104 color figures, including photographs and various bird wash drawings. Hans Peeters did the illustrations. He is an award winning painter, with two of his paintings of golden eagles appearing on Mexican stamps. The book is produced by UC Press.