Male birds and humans tend to stay closer to the nest than females do, especially when good food is around.

"This pattern is very similar to what we see in humans, with sons tending to live closer to their parents than daughters," said Dickinson, adding, though, that even female bluebirds do not fly too far away when the parents' food supply is tempting.

She said, "There are families of a father and mother with three sons nesting nearby, a daughter a kilometer (.62 miles) away, and an uncle up the hill, so it's common for family members to live quite close together."

Stephen Emlen, professor of behavioral ecology at Cornell University, formulated several theories in 1995 concerning what may lead to family stability.

He told Discovery News that one of his predictions was, "Families that control high-quality resources will be more stable than those with lower-quality resources."

Emlen said, "This is exactly what was found (by Dickinson and McGowan)."

Vittorio Baglione, an expert on ecology and evolution at the University of Vallodolid in Spain, told Discovery News that wealth "makes the situation at home more 'pleasant,' that is, risk safe, for the offspring and may be an incentive to postpone dispersal."

Baglione said other data suggest that for humans living in rural societies, "the stability of the family is linked to its wealth."

Jan Ekman, professor of ecology and evolution at Uppsala University in Sweden, told Discovery News that ample wealth also tends to lessen parent/offspring conflicts over resources, but he wondered how parents could stand having their children around for so long.

"The logical continuation of this study would be to follow up on the tolerance of offspring by their parents," Ekman said. "Does parent behavior vary with resources so that they can be made more and less tolerant by manipulating 'wealth'?"

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Name: Western Bluebird (Sialia mexicana)
Primary Classification: Turdidae (Thrushes)
Location: Western North America
Habitat: Forest edges, nesting in conifer and deciduous trees
Diet: Insects in spring and summer; fruit and berries in fall and winter
Size: Around 6.5-7.5 inches in length and 1 oz in weight
Description: Males have a cobalt-blue head, chin, throat and tail, a brown breast and a gray-blue belly; females have a brown abdomen and gray head, throat and back
Cool Facts: It is a cooperative breeder, meaning that a helper bird — which may have been reproductively active at one point — will assist the mother and father with raising and caring for their young.
Conservation Status: Common

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