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House Sparrows: Complex and Intriguing?

by David F. Westneat
Photograph by Ian R.K. Stewart

Marvels and mysteries of a common species

Unusual. Rare and elusive. Stunningly beautiful. These are NOT descriptors of the House Sparrow, that familiar, drab-looking species common to backyards and parking lots. Choosing to study House Sparrows would seem to ensure one a dull life. No adventures or extraordinary bravery in the face of extreme conditions are necessary. With some common birds, such as Red-winged Blackbirds, one can at least imagine being a stoic adventurer who slogs through impenetrable marsh in pursuit of (somewhat) elusive quarry. There simply is no romance in studying sparrows. Yet House Sparrows offer another kind of adventure—of a more intellectual nature. And as one comes to know these birds intimately, they emerge as creatures both charming and mysterious.

Consider the fact that House Sparrows live in flocks during most of the year and typically breed in clusters. Why? Flock-living creates both advantages and disadvantages that influence what individuals do in different contexts. Take, for example, the events in the grocery store parking lot when some bread is spilled on the ground. The first sparrow to find the food is caught in a dilemma. If it feeds quietly, it can eat more of the food, but it has no one else nearby to warn it of approaching danger.

Mark Elgar, a biologist at the University of Melbourne in Australia, wondered how sparrows handle this dilemma. Near a feeder he set out an intact piece of bread—the kind of food item that induces squabbles if more than one sparrow tries to feed at the same time. Elgar watched as a sparrow found the bread and ate it quickly and quietly. However, when Elgar put out the same amount of bread in the form of crumbs, the first bird to arrive gave distinct chirrup calls and only began to eat after other sparrows arrived. Sparrows thus appear to manipulate flock size to their advantage—when food can be shared, it may be best to feed in a crowd that can detect danger sooner. But when food is not shareable, a crowd would lead to costly fights, and so it is better to feed alone.

Breeding close to one another also produces some interesting, albeit distasteful behaviors. House Sparrows associate in pairs for breeding, but sometimes as many as 15 males chase a single female around the area, and they occasionally tumble to the ground in a swirling mass. Whether any of these males actually sire offspring by participating in this melee is not known, but its timing is suggestive. Males other than the mate will also sometimes display to the female as she forages below her nest site. Most of the nestlings arise from matings between two members of a pair, but about 10–15 percent are sired by a different male.

Sparrows have adapted to nesting in human structures, including holes in eaves. Occasionally, a male can defend two such holes near one another, and pair with two females. José Veiga of Madrid University noted that when this happens, the females are quite vicious to one another. The male can only assist one of the females with raising the offspring, and he prefers to help older nestlings. But the second female to arrive may try to enter the nest of the first female and destroy any eggs or chicks. If she succeeds, her offspring will hatch first and the male will help raise them. Such behavior links the familiar House Sparrow with animals like the African lion and Indian langur monkey, in which males commit infanticide just after winning control over a group of females.

For sparrows, even the simple routine of coming to your bird feeder has subtle complexities. If you look closely, you’ll notice that males have a patch of black on the throat called the bib, which differs in size from bird to bird. If you watch carefully, you would see that males with smaller bibs tend to give way to males with large bibs. Females also tend to lose preferred perches to males with big bibs, but will dispute such takeovers far more energetically than they do approaches by males with small bibs. Why females react like this is not yet known. Perhaps having a large bib indicates the male’s quality as a mate. There is evidence, however, that males with big bibs are better mates only some of the time. If this is true, then it may benefit females to confront such males and determine directly if they are as robust as they look.

This provocative idea has yet to be tested in any species. But it is the perfect example of why House Sparrows are a good subject for scientific study. They may not be glamorous, but their world is as complex as that of any other species. Their biology may reveal some important lessons about adaptation to humans. And now that I know them better, I find that my growing curiosity about them enlivens even the most routine stop at the local gas station.

David F. Westneat is a professor of biology at the University of Kentucky.

This article originally appeared in the Winter 2004 issue of BirdScope.

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