Thirty years ago, a book entitled Feed Me, I’m Yours, arrived in the parenting section of book stores. Its cover art was a photograph of an adorable, satisfied looking toddler, whose face was smeared with the colorful evidence of several food groups! The author, who specialized in parenting books, had gathered popular recipes to help parents prepare healthy foods for their tots and toddlers.
This book came to mind as I’ve been observing the goings-on among the birds in our neighborhood, in the process of raising and feeding their young. There are some radical differences in parenting between different bird species, but each apparently has a method that works, if that species survival is the proof of the pudding.
A family of merganser ducks, a hen and eight tiny ducklings, has been spending time along the shoreline near the family cabin. I’ve startled them when I take the path down to the dock, or plug in the pump that draws water for irrigating my wife’s garden. Although the common merganser is in the class of waterfowl called “diving ducks,” very young ducklings are not even capable of flight, let alone ready for underwater pursuit of fish—their primary food as an adult.
In the shallows right near shore, however, there are always schools of small minnows, as well as snails and aquatic insects that ducklings are capable of catching. It’s good that they are, too, because—while mama merganser tends them, and does her best to keep them away from danger—she generally doesn’t provide them with food that she herself has caught. She takes them where there is food to be found, leads by example, and the little ones pick it up by some combination of inborn instinct, observation and trial-and-error.
Her ducklings left the nest one or two days after hatching. In this case, “nest” was a wooden box mounted on a tree by the property owner next door. In all probability it was placed there with the hope that it would be occupied by a wood duck, which—like the merganser—is a tree cavity nester. But it is often a matter of first come, first served, and this spring a female merganser got to the box first.
Contrast this with the pair of Eastern bluebirds that are occupants of a man-made nesting box mounted on a pole in the yard. I’ve been watching both male and female as they make trips to and from the nesting box. Unlike the ducklings that left their nesting box at one or two days—the term for that is “precocial”—the bluebird nestlings are dependent on parents for between two and three weeks. They’re born helpless, and if not for the constant attentiveness of parents bringing them food, would perish.
Bluebirds have always reminded me of swallows, but they are really members of the thrush family. They are primarily consumers of insects, one reason they are migratory. They capture insects on the ground, and are said to be capable of seeing them many feet away, but are also agile enough to capture them in flight. Of course, at this time of year the adults are not doing this for themselves alone, but are returning regularly to the nest to feed their young.
Eastern bluebird numbers declined in the early part of the 20th century, due to competition from such foreign species as the European starling and the so-called English sparrow. But, like the wood duck that was brought back to abundance and to huntable numbers by artificial nesting structures, the same happy result was achieved with campaigns to erect bluebird nest boxes—“bluebird trails,” some campaigns were called—these boxes designed to keep out the larger starlings.
There are also birds that shirk some of their parental duties. The redhead duck, one of the most popular hunted species over the long history of waterfowling, has a habit—the hen, obviously—of laying eggs in the nests of other ducks, and letting the victim parent raise their offspring. This habit is called “brood parasitism.” Is it a hedge against the possibility that her own nesting might be unsuccessful?
This phenomenon has been the subject of lengthy research by biologists. Some redhead hens will lay eggs only in the nests of other ducks. Some raise their own brood in addition to laying eggs in other ducks’ nests. Some will do one thing one year, and another the next. Wetland habitat conditions—good or poor—the age and health of the hen, and the availability of other ducks’ nests nearby, are thought to all play a part in what a redhead hen does. So much for responsible parenting!
But perhaps the epitome of unconventional parenting is that of the cowbird, the most common here in Minnesota being the brown-headed subspecies. Unlike the redhead, the cowbird rears no young. It lays one egg in each nest it parasitizes, deposited for that female to hatch, feed and raise. It’s typical that the victim female is of a smaller species. The cowbird nestling is typically larger than its nest mates, hatches sooner and is therefore likely to dominate the brood. It will likely receive more than an equal share of food, and is thought to sometimes push others out of the nest.
Why this bizarre parenting behavior, thought to be unique among North American songbird species? It’s been suggested that before the American bison was pushed to the brink of extinction, cowbirds followed the roving herds and fed on the insects flushed into the air with their passage. This roving habit would not be suited to rearing a brood of young in one place. Thus, so the theory goes, the evolution of the cowbird’s brood parasite habit.
Cowbirds no longer have buffalo or open range cattle to follow. But a creature’s evolutionary blueprint is not easily altered. Cowbirds are thought to parasitize the nests of as many as 200 other songbird species. Some host females recognize the foreign egg and push it out of the nest. Others may even build a new nest layer over the old, eggs and all, and start the nesting process over again. But many are duped, and raise the “adoptee” as their own, usually at the expense of the host female’s own young.
Humans are inclined to judge other animals by our own behavior standards. We might find brood parasite behavior reprehensible as a survival strategy. But is it worse than a crow robbing a robin’s nest of all its young, or a fox killing a mallard hen on its nest, and sealing the fate of an entire brood?
Nature can puzzle, baffle and even unsettle us. But unlike us, Nature isn’t into making judgments.