In the pursuit of tracking down a comment about birds building decoy nests to confuse predators, I was led into the Audubon book and a review of nest builders. Perhaps there are bird species that boldly build a secondary nest to side-track disrupters, but other than the male house wren building several nests to offer his late-arriving mate a choice, and various birds like eagles building on top of the previous year's nest, so far I haven't found an ingenious nominee for that honor of building purposeful decoy nests. Can anyone out there in reader-land give me some short-cut knowledge about what birds build decoy nests?
It always seems that there is a certain amount of creativity allowed animals aside from their instinct dictations, and throwing a false nest trail may be a method a future individual may develop. I know unusual choices are used by nesting birds in selecting material. I remember pigeons that built a nest of wire scraps left over from BART construction. That neat assemblage of wires was presented to the Rotary Nature Center to add to a drawer full of remarkable nests, and one I recall was made completely of ticker-tape paper shreds. Each bird species has its own type of nest to house those jewel-like eggs that are uniquely designed with color and markings so consistent you can often recognize the maker by egg only.
Birds seem to have that smug look of "I've got a secret" this time of year. No doubt nearly every pair are at work on a plan and a hiding place. The game is to hide an egg-holding nest where baby birds can be kept, or boldly defend a community site such as in an egret rookery, and gather enough food to guarantee survival when they hatch. It takes considerable work to build one nest, without contending with any decoy nests. Imagine the number of nest choices available in the great out of doors, and the selections a bird must make in designing the nest, and how many trips to and fro to solve those problems! No wonder egrets are apt to steal a stick from a neighboring nest to save a trip or two!!
By April, the Cliff Swallows had returned in force along the Feather River. One cold windy day thousands sailed over the river after insects that had also been blown low. Up under the Table Mountain Bridge they would soon be plastering mud nests under the concrete overhang. Construction consists of carrying mud one mouthful at a time, and pressing it into a jug-like nest that turns to dirt when dry. I suspect well over 2,000 trips will be required to build one nest, and then how many thousand food-catching expeditions must they make? The helpless young await the life-giving gruel to promote their growth.
The altricial birds - those with helpless naked chicks - are dependent on their parent's success. Some, such as the Mourning Dove, transfuse a "milk" from their stomachs, and the tall egret regurgitates partially digested fish into the ravenous baby egrets. Many of those needy non-mobile children of many species are fed beakfuls of raw insects many times each day, so there is scant chance of secrecy when the going gets loud.
The other bird type - the mobile precocial set that quickly follows in father's footsteps - lead a "show and eat" type of feed hunt that is constantly jeopardized by hungry intruders out for some tender chick stew. Encountering the killdeer babies after they hatch from the depression-nest in the gravel is to see cottonballs running on legs that look like tooth picks while the worried parents mimic an injured bird to lure the enemy away from their progeny.
The variety of bird adaptations to a certain niche in the environment is remarkable. And for each bird specialty there is a specially designed nest of a pre-determined style. There is little fooling around trying to invent a new nest design, although different nest materials may be integrated. Sometimes you find string, pieces of plastic, and paper in stick nests, and even robins that make a combo mud and grass nest often incorporate some shreds of string or silk. Those tiny Bushtits build a giant, sock-like nest of fibers and grasses that sways in the summer breezes like a hammock in the branches, and the family is large, up to 14 mouths to feed!
The outlandish array of nest-artifacts is enough to make one a collector of egg-jewels and stick castles! In the l940's, having an egg collection was considered stylish in naturalist communities, and as a farm boy, I too, had my egg collection. I learned quite a lot about birds by raiding nests in some adverse locations.
Before I could nestle my calcium-shelled containers in their cotton bed boxes, I had to remove the yolk -and before that I had to find out where the bird lived and watch intently to get a clue of the hiding place. Bluebirds would usually be in holes in fence posts, smaller brush birds in the thickets, a crow picked a thorn tree, and the bank swallow indeed, had a hole in the bank. I scaled the sheer wall of clay and reached to the end of the tunnel to secure one lovely, pearl-like egg no bigger than an almond. I carefully took only one egg from any nest, trying to justify my property raids.
An egg in a nest is a rather strange way to begin life, yet that is the process for bird species that has proceeded for thousands of years -nay, millions. To even conceive an embryo in such a microscopic manner is a major miracle. And to put that moment of conception into a thin-shelled receptacle where it remains dormant until heated by incubation is marvelous beyond belief. Reproduction is the assignment to each pair of animals on earth, and especially in birds, we can see a progression of events that terminates in the building of a nest. Placing the nest and the eggs in a protected place affording security for brooding bird and egg alike is a message vividly recorded in the shady aisles of instinct. Wonders never cease!
© 1999 Rex Burress
April 4, 1999