Short Selections from the Newsletter Article Archive
By Jon Friedman
(Authors note: These four short articles were originally written and published by Jon and Shani Friedman in the August/September and October, 1993, issues of The Wild Bird Store newsletters. I have rewritten some segments and added pertinent information to them prior to this publication.)
When Vultures Sunbathe
Early on a Sunday morning, on the way to the Wild Bird Store bird walk at Arivaca Cienega, we were greeted by a Turkey Vulture, perched high on a telephone pole, with his impressive wings spread. Turkey vultures are sometimes observed in this pose, which is called "wing-drying" or "sunbathing." Other birds that are known to sunbathe are the Cormorants, Anhingas, Brown Pelicans, White Pelicans, and some hawks, herons and storks.
Sometimes, wet birds spread their wings in this manner. Indeed, the posture may aid in wing drying, but it is also thought to play a role in thermoregulation, i.e., regulating body temperature. In addition, sunbathing helps the perched bird in balancing; it stimulates the production of Vitamin D in the preening gland through ultraviolet radiation, and the heat and light force parasites to move to the bird's head or under its wings, facilitating their removal.
Turkey Vulture
photo by Doris Evans
For Turkey Vultures, sunbathing provides both thermoregulation and drying of wet feathers. Although warm-blooded, they are known to maintain lower body temperatures at night than during the day. Solar energy passively raises their body temperatures during morning wingspreading. The heat or energy that is absorbed during sunbathing can save or reduce the energy that the bird needs from its food, and the energy it uses to get its food. Field observations lead us to believe that sunbathing occurs more often when the Turkey Vulture is wet than when it is dry, and is associated with the intensity of sunlight.
Just before twilight, during a three-day birding trip on the lower Colorado River, we came across an unusual sight. We were several miles south of Parker and slowly driving on a dirt/farm road that paralleled the river, when we noticed a great many Turkey Vultures all flying in the same direction in the distance ahead of us. We saw an enormous old growth Freemont Cottonwood tree close to the river. This is where in excess of two hundred vultures were gathered to get the last warmth of a cool January day before settling in to roost for the night. The sight of that many vultures, all with wings spread wide to absorb as much warmth from the last of the sunlight, is one that will never be forgotten!
More info on Turkey Vultures... https://www.nationalgeographic.com/animals/birds/t/turkey-vulture/
Migration
“Is it by thy wisdom that the hawk soareth
And stretcheth her wings towards the South?”
The migration of birds interests many people more than any other aspect of bird behavior. For a long time, people knew that some birds disappeared overnight, as evidenced by the above Biblical quote from Job (39:29). Aristotle, who was a studious birder, erroneously believed that the European Robin transformed into the Redstart every fall, and the same bird re-appeared as a Robin every spring. He also believed that swallows hibernated through the winter. Even Linnaeus, who was one of the best-known naturalists of the 18th century, believed that sparrows hibernated in mud. It wasn't until the nineteenth century, when naturalists were able to travel widely in the tropics, that the concept of migration became accepted.
Migration is a regular seasonal movement from one place to another, with a return to the first place later on. It usually involves the annual cycle of arriving at and departing from a nesting site. Birds are the best-known animals that migrate, but they are not the only ones. Butterflies, salmon, eel, herring, bison, caribou, and whales all are known to migrate.
The reason that birds migrate is that their environments cannot support them year round; that is, the food supply runs out. Many people assume that it is the cold weather that drives the birds south in the fall. It may be that it is not the cold itself that the birds wish to escape, but that the food upon which they depend becomes unavailable. Even tropical birds have been known to winter-over up north if they have an adequate food supply. For example, an escaped South American Troupial lived for two years in Central Park in New York City where it was fed orange slices in the winter. It learned to bury itself up to its neck in dead leaves on the coldest of days, an unlikely behavior for a tropical bird. Seasonal changes between wet and dry conditions may also trigger migration.
The migrating bird's physiology changes to prepare it for migration. In late summer, after the breeding season and molting are over, the birds that will soon migrate begin to pick up extra fat just under their skin. The hormones prolactin and corticosterone are released by the pituitary and adrenal glands at different times of day, perhaps in response to the amount of light to which the bird is exposed. This causes a noticeable pre-migratory restlessness and fat buildup. These birds can be observed intensively feeding in one location for several days or weeks just before long flights. The increased fat provides the energy necessary for migration. Some birds arrive at stopping points during their migrations in an emaciated state and eat voraciously. Known as hyperphagia, this eating behavior serves to replenish depleted fat reserves, and fuels the next leg of their journey.
How Birds Find Their Way
One of the great ornithological mysteries of all time has been the ability of migrating birds to orient themselves to a particular direction and then to navigate to their destination. Our ancestors explained it by simply crediting Providence with the guiding of the birds. "You must not know too much, or be too precise or scientific about birds and trees and flowers," cautions Walt Whitman. "A certain free margin helps your enjoyment of these things." Only relatively recently have we begun to understand the orientation and navigation of birds.
In 1954, Gustav Kramer showed that captive European starlings would orient themselves in a consistent migratory direction as long as they could see the sun. Under cloudy skies, their ability to orient themselves properly declined. Further experiments by Kramer and his associates indicated that the birds possessed an internal biological clock that allowed them to correct their course to compensate for the movement of the sun across the sky.
However, this did not explain how birds that migrate nocturnally could find their way. Another German ornithologist, Franz Sauer extended Kramer's work by demonstrating that blackcaps, garden warblers, and lesser whitethroats (all European songbirds) would orient themselves appropriately at night when the stars were visible, but not on a cloudy night. Sauer's experiments were verified by American and Russian ornithologists in the 1960's. Experiments in 1963 and 1968 that dealt with the question of the influence of the moon failed to show that the moon plays any role in migratory orientation or navigation.
The features of the earth supply navigational aid to birds that travel by day. Many of these birds recognize the topography below them, and may determine their course by following rivers, mountain ranges, coastlines, and valleys. They may stop over at lakes, ponds and rivers along the way to rest and feed. Hawk migrations often follow mountain ridgelines where they can glide along on the strong updrafts. However, at night with all landmarks obscured, radar studies show that nocturnally migrating birds completely ignore rivers and valleys as large as those of the Mississippi.
Birds may also use wind turbulence for orientation when the stars or landmarks are obscured. They choose the nights and altitudes of flight to make use of winds blowing in the appropriate direction and at a favorable speed for flight. While waterfowl can use high-speed winds, smaller birds need lower speeds.
A curious observation has been made regarding homing pigeons. They do not utilize landmarks until they are almost home. Over a hundred years ago, it was first posited that birds were able to navigate using an ability to sense the earth's magnetic field. This was widely disputed and not well accepted for
many years. However, several experiments in the 1970's have pointed toward the confirmation of this theory.
We still have a long way to go before we can explain how any individual bird might find its way over a journey of thousands of miles. A single migratory bird may use several potential cues to guide its flight. Could it be that the birds' utilization of these cues - the sun, the stars, the earth's topography and magnetism, or the winds - might be the communication the ancients believed they held with the powers of the heavens?
THE NIGHTJAR FAMILY
Nightjars, Nighthawks, and the Whip-poor-will belong to the Family Caprimulgidae, from the Latin caper, goat, and mulgeo, to milk or suck. Ancient Greek goat herders (shepherds) who saw Whip-poor-wills hovering around their goats in the evening with their mouths gaping open, surmised that the birds were drinking the milk of their goats. In actuality, the Whip-poor-wills were gleaning insects that the goats were stirring up, and seining them from the air with their open mouths. Nevertheless, the legend persisted, and even today, they are called goatsuckers.
Lesser Nighthawk
Photo by Richard of SearchNet Media
This family is generally easier to identify by sound than by sight. As their nearest relative among the birds is the owl, they are mostly nocturnal, with some being crepuscular, that is active at twilight. In the daytime, they roost on the ground or lengthwise, not crosswise as most birds do, on low branches. No nesting materials are used, as these birds lay their eggs directly on the ground. They are masters of camouflage. Their mottled brown or grey plumage conceals them so well that they are seldom seen on the ground. If you see one, it will most likely be at dusk when it is flying about hunting insects with its mouth wide open. In Arizona, we can see and hear five species of goatsuckers.
While the Common Nighthawk is an uncommon summer resident in southeastern Arizona, it is often seen in towns, open woodlands, suburbs and towns across the United States. It bears some resemblance to a hawk when flying. Look for two bold white bars across its pointed wings, which can span up to two feet. Listen for its repeated nasal peent or beer! call. When the male performs his aerial display, he dives toward the ground and then zooms up sharply, with a "boom" of his wings. If you see a nighthawk feeding high in the air over the local mountains, it is probably a Common Nighthawk.
The Lesser Nighthawk is very common here in the summer, and there have been a few reports that it has wintered over. Although it greatly resembles the Common Nighthawk, it is an inch smaller, the bold white wingbars are closer to the tips of the shorter and more rounded wings, and its flight is more fluttery. It can most often be seen at both dawn and dusk, flying low to the ground, in lower elevations than the Common Nighthawk. Listen for its purring, trilling, toad-like call.
Lesser Nighthawk
photo by Morry Marshall
The Whip-poor-will is often heard, but rarely seen, in the wooded canyons of our southwestern mountains. Its familiar rough and hurry whip-poor-will call can be heard in the Santa Rita, Huachuca and Chiricahua Mountains. Heard close up, its song can have four syllables. It will repeat its song fifty to one hundred times, at a rate of about one per second. If flushed during daylight, the bird appears to fly away like a large brown moth, except for the white tail patches of the male. It flies smoothly about after dusk, usually near the ground, catching flying moths, beetles, crickets, mosquitoes, grasshoppers and caterpillars.
Our smallest nightjar is the Common Poorwill. Often found here on warm, dry slopes with open brush, it can also live in pinyon-juniper lands, on open prairies, or on stony slopes up to 10,000 feet. It looks very much like a small, short-tailed Whip-poor-will. At dusk, into night, and at dawn it harshly whistles a melancholy cry of poor-will or poor-Jill, if heard at a distance. If the bird is closer, you will hear a three part poor-will-low, poor-will-ee, poor-will-uck. It is also known to hibernate or become torpid.
The rarest member of the Family Caprimulgidae is the Buff-collared Nightjar. It is rather common just
south of us in Mexico, but was first reported in this country in 1958 in Guadalupe Canyon in New Mexico. It has also been found in Aravaipa Canyon north of Tucson, and the Huachuca Mountains south of Tucson. It looks very similar to the Whip-poor-will but has a tawny collar on its hind neck. Its un-birdlike call is its most distinctive feature. It utters a staccato, insect-like, accelerating song of cuk-cuk-cuk-cuk-cuk-cuk-cuk-cukacheeee, which resembles that of a katydid.
Many birders have had their first sightings or encounters with goatsuckers when, during a twilight stroll, they are suddenly stopped in their tracks by an explosion of activity as these birds are flushed, seemingly, only when about to be stepped on. They stay frozen in place, camouflaged on the ground, until the last possible moment, before startling the person whose foot is about to come down on the bird. Its abrupt take-off is nearly vertical, and the bird may fly past your face by just a matter of inches!
More info on Nightjars...
http://www.audubon.org/bird-family/nightjars