Many mating birds form lifetime partnerships — though they may have quick “flings” on the side — while others mate for only short periods or have multiple mates.
Ornithologists describe three kinds of mating arrangements: monogamous, polygamous and promiscuous. In monogamous pair bonds, the birds mate for at least the breeding season, raising their young together. Ornithologist David Lack estimated that at least 90% of nest-raised birds come from monogamous pairs. So do 80% of precocial birds — those able to walk about and feed themselves shortly after birth, such as ducks.
In many, perhaps most cases, monogamous pairs remain mated until one of them dies. Canada Geese are among the most faithful birds, mating for as long as 20 years. Most gulls also pair for life. This system is the most efficient and effective, providing the best protection and service for the brood of nestlings.
Some birds, such as House Wrens, generally stay with one mate for only one brood. In fact, while the male is raising the first brood, the female may take off, find a new mate, and begin a second nest.
In the case of polygamous pair bonds, one male or one female may have several mates. In the more common arrangement, like the harems of lore, one male has several females. This is called polygyny. Wild Turkeys, Ring-necked Pheasants, grouse, bobolinks, and Red-winged Blackbirds are polygynous. The male generally sticks with and protects his several wives and their offspring while each female takes care of raising the children. This system is more selective than one-on-one mating; the one male that is able to build a harem of several females will be stronger and perhaps healthier than the average male and will likely pass on these traits to offspring.
In a few species, the female makes use of several mates. The Spotted Sandpiper lays eggs in several nests and the males incubate them. This system, called polyandry, allows one female to produce many eggs and is useful in situations where the breeding season is short, such as in the Arctic.
Promiscuous mating occurs when two birds have sexual relations and part company. Typically, and perhaps not surprisingly, the male takes off, leaving it up to the female to raise the resulting family. The most famous practitioners of promiscuous mating are the hummingbirds and woodcocks. Dr. Stephan W. Kress, a leading ornithologist, notes that typically, either the brood is small, such as in hummingbirds, allowing the female to raise the chicks alone, or the offspring are precocial, as in woodcocks, able to walk and feed themselves soon after birth.
For a long time ornithologists thought that monogamous birds were totally faithful to one another. However, DNA testing and close observation have revealed that monogamous birds may have fleeting “affairs” with other partners.
Zoologist David Barash and Judith Eve Lipton reported in The Myth of Monogamy in 2001: “When it comes to actual reproduction, even bird species long considered the epitome of social monogamy, and thus previously known for their fidelity, are now being revealed as sexual adventurers. Or at least as sexually non-monogamous.” These include eagles and geese, long thought to be strictly monogamous.
Joel Carl Welty and Luis Baptista, in The Life of Birds, list some swans, doves, finches, hawks, wrens, flycatchers, thrushes, and warblers as birds that occasionally switch from monogamous to polygamous pair bonds.
A reader wondered if the warm weather means a sooner-than-usual appearance by hummingbirds. Probably not.
While really cold weather might slow a migration, Ruby-throated Hummingbirds are probably inspired to migrate by the angle and-or duration of the sunlight, and travel along at the same pace each year, more or less. As of Sunday, they were being seen as far north as North Carolina
Last year, the first hummers began showing up in this area around April 3.
To follow the migration, see the maps at hummingbirds.net.
Annual Meeting, Connecticut Ornithological Association, with sessions on gull identification and watching, interesting lives of local species, innovative approaches to birding, more, Saturday, March 24, all day, $20/$25, open to public, but registration required, Chapman Hall, Middlesex Community College, Middletown, ctbirding.org.
9,000 acres of protected estuary habitat in New York City, Sunday, March 25, 7 a.m. for carpooling, vanning, Saw Mill River Audubon, 914-666-6503, [email protected]
Bird Watching 101, “a good foundation for enthusiasts,” Saturday, March 31, 1 to 3:30 p.m., $15/adult, kids free, Audubon Greenwich, 613 Riversville Road, RSVP to Ted at 203-869-5272 x230.
Seals and Seabirds cruises, two and a half hours around Norwalk Islands, Saturday, March 31, at noon and Sunday, April 1, at 1 p.m., $20.50, Maritime Aquarium, Norwalk, 203-852-0700, ext. 2206, maritimeaquarium.org
Copyright 2012 by Jack Sanders. Send sightings or comments to: jackfsanders [at sign] gmail.com, or to Bird Notes, Box 1019, Ridgefield, CT 06877. If you need help identifying a bird, try your local nature center. If you find an injured bird, call wildlife rehabilitator Darlene Wimbrow of Redding, 203-438-0618, Wildlife in Crisis of Weston, 203-544-9913, or Wild Wings of Greenwich, 203-637-9822. The columnist’s website is www. sandersbooks. com.