Meeting Abstract
Urban birds often incorporate man-made materials in their nests and these materials often resemble natural materials typically used in nest construction. The use of man-made materials may, however, increase entanglement risk of both adults and nestlings. The western bluebird (Sialia mexicana) is a common songbird in southern California that readily nests in nest boxes in open, park-like habitats. We documented the types and amounts of man-made debris and measured entanglement rates in 75 western bluebird nests from four sites (two parks and two cemeteries) in Orange County, CA. We surveyed for man-made debris in the habitat surrounding each nest box. Western bluebirds used long, thin, and flexible plastic, paper, and fabric items that resembled natural materials in their general properties (106 +/-18.8 items/nest, mean +/- S.E.). Easter basket grass was the most commonly found man-made item in nests. Fifty-nine nests contained broad debris for which there was no obvious natural analog. Unlike the flexible, mostly cellophane, broad man-made items, broad natural materials may not fit easily through the nest box opening. Broad man-made objects may serve a novel function lining the cups of western bluebird nests. The amount of man-made material in each nest was not correlated with debris abundance surrounding its nest box; at the site level, however, environmental debris abundance was correlated with nest debris abundance. Of the 262 nestlings monitored only two died of entanglement suggesting that western bluebirds may be at low risk of entanglement and are relatively well suited to urban settings with man-made debris.
