Foraging ecology of the California gnatcatcher deduced from fecal samples

Abstract

The California gnatcatcher is a threatened species essentially restricted to coastal sage scrub habitat in southern California. Its distribution and population dynamics have been studied intensely, but little is known about its diet. We identified arthropod fragments in 33 fecal samples of the California gnatcatcher to gain insight into its foraging ecology and diet. Fecal samples were collected from adult males, adult females, fledglings, and nestlings. Leaf- and planthoppers (Homoptera) and spiders (Araneae) predominated numerically in samples. Spider prey was most diverse, with eight families represented. True bugs (Hemiptera) and wasps, bees, and ants (Hymenoptera) were only minor components of the gnatcatcher diet. Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets (Orthoptera) and spiders than adults consumed themselves. Both adults 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 habitat.

Diet switching of seed-eating birds wintering in grazed habitats of the central Monte Desert, Argentina

“…Complementariamente, las heces defecadas por el ave tanto en el lapso en que estaba atrapada en la red como durante su estadía en la bolsa de tela y durante el período de procesamiento fueron colectadas meticulosamente e incorporadas a la muestra correspondiente. La estimación de la dieta de aves a partir del análisis de muestras de las heces ha probado ser exitosa en numerosos estudios (e.g., Calver y Wooller 1982, Ralph et al 1985, Rosenberg y Cooper 1990, Burger et al 1999 y referencias citadas en estos trabajos), sobre todo si se la combina con otras técnicas, como en este caso. Finalmente, a varios individuos que murieron por distintas causas durante el perío-do de estudio se les removió el tracto digestivo completo.…”

Background matching behaviour and pathogen acquisition: plant site preference does not predict the bacterial acquisition efficiency of vectors

“…Homalodisca vitripennis (Germar), for example, consumes between 10 and 100 times its dry body-weight hourly (see Redak et al 2004). During such lengthy feeding episodes sharpshooters are exposed to a range of visual predators including jumping spiders (Salticidae), assassin bugs (Hemiptera: Reduviidae), lizards (Lopez et al 2003;Suttle and Hoddle 2006;Fournier et al 2008), and potentially insectivorous birds (Burger et al 1999).…”

Do Female Spiders Select Heavier Males for the Genes for Behavioral Aggressiveness They Offer Their Offspring?

“…It was also convenient because birds were not harmed by sampling. For instance, in a study of the threatened California gnatcatcher (Polioptila c. californica), fecal samples showed that the adult gnatcatchers selected more and larger prey, including spiders, to feed their chicks than adult birds ate themselves (Burger et al 1999). However, there was constantly a risk that estimations of prey numbers would be biased.…”