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Swifts

by Mike Scully

This article first appeared in the July 2004 issue of the San Antonio Audubon News.

The swifts (Apodidae) are among those creatures whose very existence seem shrouded with an air of improbability. Imagine a bird so completely adapted to an aerial existence as to be rendered incapable of walking and which, instead of perching, must cling to vertical surfaces like a bat. Swifts customarily bathe, mate, drink and in some cases even sleep on the wing. Streamlined profiles and long, swept-back wings enable them to reach quite incredible flight speeds; our familiar Chimney Swift (Chaetura pelagica) is reportedly able to handily exceed 100 mph in level flight.swifts flying

Even master aerialists must descend to earth to breed, most swifts constructing their nest either partially or completely from their own glue-like saliva. If a nest made from saliva sounds improbable, perhaps even more so is the fact the saliva nests of one species are used to make an Asian delicacy.

Like the swallows, swifts feed upon flying insects captured in sustained flight. Unlike swallows however, swifts are among the few groups of birds able to enter a torpid state, enabling adults and young to slow down their metabolism during periods of inclement weather.

The family Apodidae is divided into three subfamilies. The enigmatic Black Swift (Cypseloides niger) is our sole representative of the subfamily Cypseloidinae. The members of this New World group feed preferentially upon swarms of winged ants and termites. Black Swifts nest on rocky cliffs, typically placing their nest on a ledge behind falling water. They lay but a single very large egg, and the well-insulated young swift waits patiently while the adults travel enormous distances to forage. The young remain in the nest for more than six weeks. Incredibly, the evidence indicates that the young swifts migrate immediately upon fledging, their maiden flight being a journey to Central America.

The White-throated Swift (Aeronautes saxatalis) is our sole representative of the subfamily Apodinae. Swifts in this group have feet that are adapted to grasp laterally, enabling these swifts to roost in crevices on cliffs. White–throated Swifts nest in small colonies, the nest of glued-together feathers and plant fibers placed within a rocky crevice or, more rarely, in a similar site on stone or concrete buildings. Three to five young are raised each year, in common with other swifts the young are fed large boluses of food composed of a mass of accumulated insects mixed with saliva. Outside of the breeding season, flocks of up to 200 of these swifts have been recorded gathering to roost in a single cliff face crevice.

While one has to travel to the Western States to see the previous two species, the Chimney Swift is common across much of the United States, the similar Vaux’s Swift (Chaetura vauxi) replacing it in the Pacific Northwest. Both species nest and roost in large hollow trees, the Chimney Swift also accepting man-made substitutes. Common to their subfamily Chaeturinae, these swifts have stiffened tail feathers which function to support the birds as they cling to vertical surfaces.

Both species construct a new nest of saliva and dead twigs each year, the twigs collected by the remarkable method of being broken from dead branches by the feet of the swifts as they make close passes in flight. Three to six young are the norm, the young fledging in about 30 days. Unlike many swifts, neither of these species nest colonially, such that one large hollow tree or chimney usually contains only a single breeding pair, contributing to the already short supply of breeding sites. Perhaps as a result, Chimney Swifts are unusual in that they accept helpers; unmated adults who help raise the young. Outside of the breeding season, both these swifts famously gather in large flocks to roost.

While Vaux’s Swifts were known to winter in Central America, for many years the main wintering area of the Chimney Swift remained a mystery. The answer came when two colorful little bands were noted in the headdress of an Indian from a remote region of Peru. It turned out that these bands had come from a Chimney Swift banded in the United States, perhaps the most remarkable banding recovery of all time.

Sources and More Information:

http://www.dlia.org/atbi/species/animals/vertebrates/birds/apodidae/chimney_swift.html
http://www.ohiodnr.com/dnap/OhioBirding/Bird%20PDF/ChimneySwift.pdf
http://tbba.cbi.tamucc.edu/accounts/chsw/chswacc.htm
http://www.nwf.org/nationalwildlife/dspPlainText.cfm?articleId=788
http://fwie.fw.vt.edu/states/nmex_main/species/041995.htm
http://www.int-birdstrike.com/proceedingspdf/BUURMA.pdf
http://fan.nb.ca/fan/info/Recreation/BirdWatching/Swifts.html
http://fan.nb.ca/fan/info/Recreation/BirdWatching/Swifts.html#FIVE
http://animaldiversity.ummz.umich.edu/site/accounts/information/Chaetura_pelagica.html
http://home.austin.rr.com/dwa/Chaetura%20(VOL%208)%202003.pdf

 

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