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June 4, 2010 > Nest-sharing in the bird world

Nest-sharing in the bird world

By Suzanne Ortt
Photos By Doris Nikolaidis

Nest sharing by two bird species, previously an occasional phenomenon, is now on the increase. Could it be that the economic recession impacts the bird world? In reality, one report of this behavior occurred as early as 1907.

Scientists study this. Bird lovers observe it. My next-door-neighbor has experienced this firsthand. She has a birdhouse that, for the past two years, has been shared by Plain Titmice and Chestnut-backed chickadees. So the focus is on these two members of the Paridae family. After eggs are laid, incubating duties may be shared but this is unverified. After babies are born, the parents definitely share feeding.

Titmouse's unusual name joined "mase," the Old English word for bird, and "tit," denoting something small. A titmouse, averaging four to six and one-half inches long, has two noteworthy traits. It tricks predators with its call, a loud scold that fades as if the bird is moving away. Predators search for the ventriloquist bird while the trickster remains hidden nearby. Another feat is that a titmouse eats with its feet. It balances on a branch, uses its feet to hold seeds, and opens them.

Titmice do not construct their own nesting cavities. They use natural holes in trees, abandoned cavities, and artificial nesting boxes. This habit may contribute to the nest sharing behavior.

The chickadee is "cute," with its oversized round head, tiny body, and active curiosity. Its name is derived from its alarm call, "chick a dee dee dee." These acrobats seldom remain at feeders except to grab a seed to eat elsewhere. Chickadees are common in residential areas.

Contemporary birding literature details probable causes. Birds may recognize the advantages of shared body warmth, security and food. Experts theorize sharing is due to multiple cavities in some nest boxes. Birds leave one cavity and return to roost in the wrong hole, one already occupied. Another could be one bird unwittingly laying its eggs in the active nest of another. A third is a lack of nesting sites in some areas.

Observers have seen other bird species involved in mutual nesting. Barn owl nest boxes attract jackdaws, kestrels and stock doves. Blue tits and great tits share with pied flycatchers. Cardinals and robins practice this trend, despite the cardinals' known aggressive behavior.

Perhaps communal nests lurk in your neighborhood. Watch for it next mating season.

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