Foraging ecology of the California gnatcatcher deduced from fecal samples

The California gnatcatcher is a threatened species essentially restricted t o coastal sage scrub habitat in southern California. Tts distribution and p opulation dynamics have been studied intensely, but little is known about i ts diet. We identified arthropod fragments in 33 fecal samples of the Calif ornia gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and ne stlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predomina ted numerically in samples. Spider prey was most diverse, with eight famili es represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenopter a) were only minor components of the gnatcatcher diet. Gnatcatcher adults s elected prey to feed their young that was larger than expected given the di stribution of arthropod size available in their environment, and chicks wer e provisioned with larger prey items and significantly more grasshoppers an d crickets (Orthoptera) and spiders than adults consumed themselves. Both a dults and young consumed more sessile than active prey. Further studies are needed to determine whether arthropods sampled in coastal sage scrub that are common in fecal samples are good indicators of California gnatcatcher h abitat.