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Mallards, cardinals, seedeaters, and fruit eatersAnswers to readers' questions about mating, pairing, and foraging Contributed by Julie Craves
Published: April 23, 2004
On a nearby lake, there are 10 Mallards, consisting of two mated pairs and a bunch of bachelor males. I recently noticed some drakes trying to mate with each other. Is this unusual behavior in Mallards? — Georgia Fox, Chico, California
In North American wintering populations of Mallards, the ratio of males to females is skewed slightly toward males. Winter is the time of year when Mallards choose mates. The imbalance can lead to a shortage of hens. In crowded or urban settings, Mallards form trios, most often made up of two males and one female. Because the urge to mate is very strong, the males will attempt to copulate with each other when there are fewer hens than drakes. It has been estimated that 2-19 percent of all Mallard pairs consist of two males. Typically, the pairs don't attempt to mate with each other, although some paired drakes will try to mate with males other than their mates. Same-sex pairings have also been reported in the Canada Goose and other types of birds, including gulls and pigeons.
A cat claimed the life of a female cardinal in my yard. Will its mate bond with another female? — Michele Chartier, Warwick, Rhode Island
Not to worry. The male will soon find another mate. Cardinals are monogamous, but they don't really mate for life. Some may remain paired year-round, but pairs break up between and even within breeding seasons. Whether lost to "divorce" or death, the absent mates are replaced with other unmated birds even during the nesting season or shortly thereafter.
Among other monogamous bird species, many stay faithful for one nesting season or just a single brood. Others may keep the same mate for several seasons. A few seasons, of course, may amount to a small songbird's lifetime.
DNA fingerprinting has enabled researchers to determine the exact parentage of individual birds. The technique has led to the discovery that birds formerly presumed to be monogamous are not as faithful as was once believed. While birds may be socially monogamous and have only one "mate," they will sneak away and mate with other birds. The behavior is known as extra-pair copulation. Both females and males engage in the strategy, which makes sense from an evolutionary point of view. Males are able to sire more young if they mate with more than one female, thereby passing on more of their genes. Females are able to raise a clutch of genetically diverse offspring, fathered by various males, increasing the chance that some will be more "fit" than if all had been fathered by a single partner.
Is there a way to find out which birds are seedeaters and which are fruit eaters? — Peggy Morgan, Van Wert, Ohio
There are plenty of books that describe the diets of birds, but there is also a quick-and-dirty method. It starts with a simple question: What does the bird's bill look like?
In general, seedeaters have stout, often cone-shaped bills suitable for cracking open seeds. Insect eaters tend to have more specialized bills, depending on their foraging method. For example, many warblers have narrow, pointed bills, which the birds use to probe leaves, bark, and buds for insects. The American Redstart shares a flattened, broad-based bill shape with flycatchers. The more aerial the foraging method, the wider the bill. In North America, there aren't any strict fruit specialists. The closest are the waxwings. They rely heavily on fruit, but they eat a good number of insects, too.
Julie Craves is supervisor of avian research at the Rouge River Bird Observatory at the University of Michigan Dearborn and a research associate at the university's Environmental Interpretive Center.
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Read more by Julie Craves.
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