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Why do bluebirds carry fecal sacs from their nests for disposal away from the nest site? Is this good housekeeping or something more?  A recent study in Georgia found that Eastern Bluebirds behaved as do many other bird species in sac removal.  Their behavior is consistent with the hypothesis that fecal sac removal is done to reduce cues predators use to find nests.  The published study, Observations of Fecal Sac Removal by Eastern Bluebirds, written by Jason D. Gowaty, appeared in the journal The Condor (104:205-207).

“We observed Eastern Bluebird parents place nesting fecal sacs high on electric wires,” the authors wrote. “This stimulated our interest in fecal sac removal, which occurs commonly among bird species, yet remains a neglected topic in studies of parent behavior.  Observations support the explanations that fecal sac removal keeps nests dry and clean and reduces exposure to pathogens and parasites, but if these were the only reasons parents removed fecal sacs, one might expect parents to drop fecal sacs just outside their cavities.  Alternatively, if fecal sacs removal reduces cues predators use, parents should dispose of fecal sacs far from nests.”

The study was conducted from March through August in the years of 1995 through 1999. Eastern Bluebirds were observed feeding young and removing fecal sacs at 348 nests on 128 territories at four sites near Athens, Georgia.

“With the exception of balancing fecal sacs high on electric wires, Eastern Bluebirds seem to behave like other species when removing fecal sacs from nests,” the authors wrote.

“American Crows and Florida Scrub-Jays placed fecal sacs on branches…. Prothonotary Warblers carried fecal sacs about 120 feet to 300 feet before dropping them and Tree Swallows carried sacs between 60 and 160 feet.

The study showed that the Bluebirds deposited fecal sacs from 120 to 300 feet from the nest, flying from 60 to 150 feet farther on these trips than on trips when no sacs were carried.  Bluebirds were observed placing fecal sacs on wires, wooden fence posts, tree branches, and, once, atop a utility pole.  If the sac was dropped during the disposal trip, bluebirds sometimes caught the sac in mid-flight and continued the disposal effort.

“Bluebirds removed 95 percent of fecal sacs during feeding trips, rather than making special trips for this purpose…Female and male parents do not differ in removal rates or disposal of fecal sacs.”

“Because adults traveled farther than usual to dispose of fecal sacs, we conclude that the current best explanation for fecal sac removal by adult Eastern Bluebirds is reduction of cues, visual or chemical, that predators might use for finding nests,” the authors wrote.

Article from Bluebird, Journal of the North American Bluebird Society, Summer 2002, Vol. 24, No. 3

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