NESTS, EGGS AND NESTLINGS (4/26/02)

This is the perfect time of year to respond to your questions about the nesting of birds. Fortunately, I won’t have to do any work, since you can find your own answers in this new book, A Guide to the Nests, Eggs and Nestlings of North American Birds by Paul Baicich and Colin Harrison. Now, you can find out everything you want to know about the breeding cycle of our chickadees, titmice, cardinals, sparrows, doves or any other back yard bird.

As you might surmise from the title, this is a comprehensive guide to the breeding biology of 669 species, from the type of habitat that each prefers, along with the nature of the nest site, nest construction, breeding season, eggs, incubation and length of the nesting period. The text is accompanied by 13 colored plates of herons, gulls and various precocial young (those, like ducks and chickens, that are ready to follow their parents around as soon as they leave the egg and dry off) and 49 plates that show the eggs of our songbirds. Attractive black-and-white drawings also accompany some of the birds.

Just for interest’s sake, I first looked up house finch, just to see what the authors had to say about the nesting sites of these birds. As I might have known, they had a textbook answer: “Breeds in cultivated areas and around buildings; nests in a variety of sites, where a raised ledge or cavity is available.” What I was hoping to find was a “real-world” answer indicating that they are the birds most likely building a nest in your hanging porch plants. The same comment applies to robins; not a hint that they are attracted to wreaths, real or artificial, on the doors of houses.

Next, I gave Carolina wrens a try. This time the information was a little more realistic. After the usual Mother Nature settings, comes this: “Also in almost any cavity or niche around buildings and man-made structures, including nest boxes.” That was close but didn’t really tell it like it is. Those who post to the MassBird have been exchanging information on the interesting crannies, nooks, crevices, openings, cracks, fissures and the like where they have observed these ingenious wrens nesting. The general conclusion has been that they like the complete cover offered by sheds, garages, open porches and garages and will take advantage of virtually any small partially-enclosing item.

That these wrens are versatile is an understatement. Here are a few examples. One member reported that he discovered a nest with one egg six inches down in a 6"x2'x2' garage door counterweight on top of sand and a variety of stones, golf balls and other heavy objects attached by cable and pulley to the door. Each time the door was closed at night, the counterweight and nest were raised close to the garage ceiling well out of sight. During the day, the mother wren had no difficulty sneaking in and out unobserved. Not a bad arrangement when you think of it, closed in out of the cold at night with plenty of spilled birdseed and spiders and free to come and go during the day!

Garages may be a favorite of these crafty birds, as here is another story. “The nest was built on top of a car roof rack support bracket (the old kind that clamped to the car's rain gutter) which was roughly horizontal and leaning in a corner. The nest was built of plant stems, maybe grass, and was more or less the size and shape of a coconut (with husk). The entrance was a hole in the side, so the interior was almost totally enclosed and hard to see. The nest was about a foot from the garage door, and they stayed in spite of having the garage door opened and closed and the car being driven in and out only a couple of feet from their nest. Curiously, the adults always seemed to enter and exit the garage through an opening in the back door where a pane of glass was missing, never through the main garage door (to avoid leading predators to the nest?)”

I have had Carolina wrens nest in my clothespin bag hanging on the line, and another MassBirder discovered a nest “In my newspaper customer's mailbox (next to the paper tube). Every time I delivered I had to beware of a madly exiting wren!”

Although these wrens do not often choose one of the standard nest boxes, one MassBirder reported, “I may have finally stumbled onto a Carolina Wren's nest box design that works. It appears to be the round door entrance that keeps them away. After years of failure with traditional boxes, a pair of Carolina Wrens is now building a nest in a box by entering through a 2-inch ventilation gap in the rear. This gap spans the width of the box and is located at the intersection of the roof and the rear wall. The box also has a traditional entrance hole in the front, but the wrens bypass it to enter from the rear. Box dimensions are 8 inches wide x 12 inches long, by 8 inches deep. It is mounted on a support beam under my rear deck. May be a fluke, but worth a shot if you are not having any luck with a traditional nest box.”

What can you add about Carolina wrens (or any other quirky bird) to these stories? emiller@seepub.com