Dunn County News, WI – Jul 23, 2014
By Dennis Weibel, Red Cedar Notebook
Last month, millions of people from around the world took part in the Internet vote to name seven new “Wonders of the World.” It seems that some folks were disappointed that only one of the original wonders was still in existence. They longed for a new list of wondrous architectural achievements, ones that could be viewed and visited in the 21st century.
I have long been an admirer of human architecture, from the stunning brilliance of St. Peter’s Basilica in Rome to the stoic grandeur of our very own Mabel Tainter Memorial Building, but I also marvel at the constructions of other animals. For thousands of years, animals have used residential materials, anatomical adaptations and a bit of ingenuity to build marvelous structures, from beehives to beaver dams.
Engineering marvels One such construction is the mud nest of the cliff swallow (Petrochelidon pyrrhonota). Examples of these can be found under the bridges that span the Red Cedar River and trail. My favorite spot to observe both the nests — and the birds that built them — is from the Red Cedar State Trail underpass at Irvington.
The swallows, themselves, are easy to see. They continuously swoop through the air in eye-straining patterns, rarely pausing to perch. Most often, they appear to be dark brown, but with just the right light and angle of view, the iridescent blue-gray feathers on their crowns and shoulders glimmer and catch the eye. Cliff swallows have a squared-off tail and a pale orange rump patch, features that distinguish them from other swallows found in Dunn County.
These swallows prefer life in a colony, rarely constructing a solitary nest. You can easily spot their numerous, conical, gourd-like nests plastered to the underside of the bridge. They are made out of mud pellets, carefully carried to the site in the beaks of swallows.
Frequent flyers
This past spring, I watched newly-returned cliff swallows congregate on the mud flats just south of the bridge. Scores of birds scooped up beakfuls of mud, flew to the bridge, deposited the mud pellets and flew back. They repeated the process over and over and over. The average nest contains 1,000 to 1,400 mud pellets, or trips from mudflat to bridge.
A few lucky swallows avoid this tedium altogether. They migrate back early to take up residence in one of the previous year’s nest, having to make only minor repairs. In this situation, the early bird truly does “catch the worm.”
Upon completion of repairs or construction, the nests are lovingly lined with grass and feathers. The female then lays four to five eggs.
My very rough count of nests stuck to the four large I-beams that support the Irvington Bridge comes to about 200. With four eggs per nest, there were, at one time, possibly a whopping 800 eggs waiting to hatch.
Safety in numbers
Bob and Mary Brown from the University of Tulsa have spent 20 years observing and studying cliff swallow colonies. They have determined that there is safety in such large numbers. The massive volume of eggs and nestlings tends to overwhelm predators and dilutes predation of the young. (If you wish to learn more of the Brown’s research, visit their Web site at: www.bio.utulsa.edu/Brown.htm.)
If you visit the bridge anytime soon, the plaintiff cries of hungry babies will tell you that the eggs have hatched.
Feeding these newly-hatched nestlings is a monumental task. Cliff swallows dine exclusively on insects, favoring flies, beetles and mosquitoes. Their long, pointed wings allow for quick, maneuverable flight, handy for chasing tiny insects in mid-flight.
Air traffic
Each day, the adults make thousands of forays, ceaselessly catching insects and depositing them into small gaping mouths. With some 800 mouths to feed, flights in and out of the Irvington Bridge rival those at O’Hare International, with nary an air traffic controller in sight.
The multitude of young cliff swallows will likely fledge (take flight for the first time) in the next few days. When they do, they will congregate in large groups called crèches.
The adults will continue to feed the young throughout this period. Imagine, if you will, the dilemma of flying up to a crèche of 50-60 juvenile birds, mosquito in beak, and trying to locate that sweet little face you call your own. The adults and young overcome this obstacle through a series of vocalizations.
When autumn is ready to turn the world over to winter (something I care not to think about right now), we will need to say good-bye to these avian architects. Cliff swallows are some of the world’s premier migrators. They will fly to the southern regions of South America to escape the cold of the upper Midwest.
Come spring they will rejoin us, grab some mud, build new nesting structures and start the circle of life anew.
In our next column, we will take a look at a plant some people consider a weed, while others look upon it as a “jewel.”
