Wednesday, July 16, 2008

BIRD MIGRATION - A TRUE WONDER OF NATURE

Believe it or not—it’s migration time already! And there are plenty of places around Southern California to find fall migrant birds such as warblers, vireos, thrushes, flycatchers--and who knows what rarities?

The summer months can be sketchy for finding birds, but from now through October, the opportunities increase as any island of green may attract a flock of migrants to rest and feed. City parks with lots of trees and a water feature such as a lake, pond, or stream will top the list, as will business parks.

Migration is one of Mom Nature’s true wonders, when millions of birds fly south to their wintering grounds in Mexico, Central and South America. Because they are on the wing at night (to avoid predators and take advantage of cooler temps and less wind), humans rarely see them. They have been picked up on radar and the images are astounding; here’s some links:

http://www.srh.noaa.gov/key/HTML/springmigration.html

http://www.radar.mcgill.ca/bird_migration.html

http://www.leo.lehigh.edu/projects/birds/migration.html

A simple Google search will turn up many more pages for those interested in learning more about these feathered wanderers.

Bird migration is one of the most astonishing feats in nature. Each spring and fall, birds from geese to hummingbirds find their way through the night sky, braving weather, human hazards such as high-rise buildings and communications towers, to follow their biological imperative.

Some birds fly thousands of miles non-stop; an amazing feat for such small and seemingly vulnerable creatures. One can only imagine the beauty and terror of such a journey, sometimes over open water with no land for hundreds of miles. Their strength and bravery are to be admired and respected.

To fuel these long distance flights, birds fatten themselves up by gorging on food prior to the journey:

“A maximally fattened warbler may weigh 12 grams or more, nearly double its lean body mass. The caloric density of this amount of fat is more than sufficient to supply the energy demand of a small bird like this for making a non-stop nocturnal migratory flight of 400 miles or more--and this is just one of several such flights needed to take it all the way from its Canadian nesting grounds to its Central American wintering grounds! And to think, each small warbler is just one of hundreds of thousands of small songbirds making these journeys, traveling across vast stretches of sky by night, sheltering in forests and fields by day, over and around each and every one of us at this time of the year.” [http://www.westol.com/~banding/Pictorial_Highlights_09291005_2003.html]
One of the most interesting uses of modern technology to track migrating birds is radar. It seems incongruous at first: using something so high tech to track behavior that may be more ancient than humankind! But it is an amazing tool and allows us to see the sheer magnitude of this avian effort:
[From: http://virtual.clemson.edu/groups/birdrad/COMMENT.HTM]

Migrating Birds : Exodus
Birds migrating at night frequently depart 30 to 45 minutes after local sunset, and this departure is visible on radar. As birds leave their diurnal stopover sites and climb to typical altitudes of migration, they enter the radar beam and begin reflecting energy back to the antenna. Such departures appear as rapidly expanding circular (or nearly circular) patterns in a base reflectivity image as more birds climb into the radar beam. By examining radar imagery in this window of departure times, CUROL can identify specific areas from which large numbers of birds are departing.

These areas, often called "hotspots," are the diurnal stopover sites in which migrant birds have spent the day feeding and resting in suitable habitat. Because all habitats are not suitable for migrant birds and because many landscapes are increasingly fragmented and unequally distributed across the landscape, hotspot phenomena appear even more striking. These areas consistently appear on radar images as areas of high bird activity. Delineating areas of high bird activity is a priority for bird conservation, and studying hotspots on radar is an essential tool for this endeavor on a large scale.

The following reflectivity image from the evening of March 31, 1999 at HGX Houston, TX illustrates the premise of "hotspot" phenomena. Notice the areas of higher reflectivity (the reds and purples analagous to densities of 60-500 birds per cubic kilometer) that appear prominently (against the yellow and orange background) around the radar stations. See that the time, given in UTC at 0122Z (6 hours ahead of local CST), is approximately 30-45 minutes after local sunset. This image is a characteristic "hotspot" frame, in which we can see specific areas from which large numbers of birds are departing.



The reflectivity image below shows a striking amount of departure detail east of the station.




One of my favorite conservationists, the late David Gaines, had this to say about birds:

“…the paths they travel, while beyond human design, are parallel with our own. They have as much right to be here as we do—not because they are useful or beautiful, but because they are kin.”

We often forget that we are a part of nature too, but instead of living in harmony with nature, we have shed our wildness in favor of living in ‘forests’ of concrete and steel. What is needed is to get back out into the real natural world and re-establish our ties with other wild creatures—creatures who are never far away, yet are so distantly estranged from us by our myopic modern vision. We need to unplug and go forth into forest and field, to let the wind caress us and bird songs fill our ears with nature’s music.

The beauty that can be found in the humblest of places, such as a vacant field; or in man-made nature, such as a city park, are worth seeking out. There are so many state parks and wildlife refuges in every county of Southern California that it’s easy to spend a day away from the world of traffic and commerce.

Adventure awaits! Leave your daily grind behind and enter nature with your whole heart and mind. Find the reward of seeing a butterfly on a flower or a colorful warbler gleaning insects from a tree branch. It’s all there. All you have to do is open your eyes and ears. Nature is ready when you are.

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