A female goldeneye patrols from behind as its ducklings go for a swim. Credit: Courtesy of Bob Duchesne

Father’s Day is complicated in the bird world. Even if fledglings could buy a Hallmark card, they often wouldn’t know where to send it.

Parenting strategies have evolved, sometimes in unusual ways. For each species, nature favors whatever strategy passes on the most genes to the next generation. For about 85 percent of the species in the world, that means both parents help raise the chicks. Sort of.

While most species rely on two-parent care, actual parentage can be questionable. Many birds fool around.

Fathers end up raising another male’s offspring. Sometimes it’s because the female snuck off for a quickie.

At other times, especially in nesting colonies, the expectation of monogamy is loose. Whenever there are too many males near too many females, the tendency toward unfaithfulness is high. Whenever nesting conditions inhibit the ability of males to see and ward off rivals, such as when birds nest out of sight in wetlands and grasslands, infidelity is common.

It’s probably unfair to say that grassland birds are unfaithful. Rather, they adopt a breeding strategy where fidelity is not that important.

Bobolink males defend a territory. Females build their own nests in that territory. But her nest may be filled with the eggs of several fathers. Meanwhile the male bobolink may provide food for more than one set of nestlings. Often, they will have a primary nest, helping their mate feed the youngsters in it, but they will also provide supplemental feeding to chicks in a secondary nest.

Females can also get stuck raising the young of another bird. When one female leaves the nest long enough to feed, another might sneak in and dump an additional egg. Many waterfowl do it, thus “ducking” their responsibilities. Cavity-nesters, such as wood ducks and common goldeneyes, seem particularly vulnerable.

The Bicknell’s thrush is an uncommon alpine bird in Maine. Up there in the dense spruce of the mountaintops, fidelity is not a cherished virtue. Males don’t even bother to hold territories. So many genes get spread around that males ensure the survival of their own offspring by feeding everybody else’s.  It’s a virtual hippie commune up there.

Even when both parents are tending their own nestlings, responsibilities may differ. For the majority of birds, the male provides most of the food, while the female protects the youngsters from threats and weather. But for the abundant red-eyed vireos in Maine, those roles are reversed.

In about 1 percent of the world’s species, the male has sole responsibility for tending the kids. That duty falls on the female about 8 percent of the time.

Roughly 9 percent of species shift roles completely. Polyandry occurs when the female lays the eggs, but then the male takes over brooding and chick-rearing, while the female abandons the nest. She’ll mate with multiple males, and once she’s laid the eggs, her duties are done. In Maine, spotted sandpipers fall into this category.

Alternatively, some polyandrous birds share partial responsibility. The female lays the eggs and incubates them for a short time. Then the male takes over incubation, and she goes off to start another brood with another male. However, she takes sole responsibility for rearing that second family, while the male departs for fall migration. Sanderlings follow this strategy. Although they nest in the high Arctic, sanderlings flood beaches from Maine to Florida in the offseason.

A variation on this strategy is practiced by two western species, the Harris’s hawk and the acorn woodpecker. Multiple males mate with a single female. All of the fathers help to raise their blended family together.

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Finally, there are species where the father plays no role whatsoever in raising his offspring. Typically, these are birds that use leks. That is, males defend a territory and display continually throughout the breeding season, attracting and mating with as many females as possible.

Grouse species largely follow this strategy, including Maine’s ruffed grouse and spruce grouse. American woodcocks do it. Many grouse and prairie-chicken species in western states establish leks.

Wild turkeys adopt a similar tactic, except that males tend to wander around to advertise, rather than attracting females to their breeding grounds. A tom entices a small harem to congregate for romantic purposes. When a hen succumbs to his charms, copulation ends the romance. She may merge her family with other hens, and wander around in bigger flocks through summer, but males play no further role in chick-rearing.

Ruby-throated hummingbirds are absentee fathers. In fact, all hummingbird species practice love ’em and leave ’em. No Hallmark cards for you.

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Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.