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Foraging behavior of Tufted Tit-Tyrants (Anairetes parulus) in semiarid northcentral Chile.

Article Excerpt
The Anairetes (Tit-Tyrant) flycatchers of South America inhabit dense scrublands and forested regions from southern Colombia to Patagonia; one species is endemic to the Juan Fernandez Islands (Ridgely and Tudor 1994). Six species are included in the genus (Ridgely and Tudor 1994, Roy et al. 1998) in the subfamily Elaeniinae, which is closely aligned with Selpophaga tyrannulets (Birdsley 2002). Anairetes have been termed "titlike tyrants" (Goodall et al. 1957) or "tit-tyrants" (de Schauensee 1966), reflecting behavioral and morphological similarity with Holarctic parids (chickadees and tits). Other authors have compared the foraging behavior of Anairetes to Holarctic regulids (kinglets) (Jaramillo 2003). The most widespread species of the genus is the Tufted Tit-Tyrant (A. parulus), which occupies diverse habitats including Andean pre-Puna scrub, desert scrub, Valdivian forest, and other shrublands. It occurs in most scrublands and forests in Chile below 2000 m (Jaramillo 2003). This species is insectivorous and its broad habitat, and latitudinal and altitudinal distributions suggest it is a habitat generalist. Their energetic style of foraging has been described as appearing to be "in constant motion, more so than most other gleaning tyrannids" (Smith 1971: 269). However, their foraging behavior and habitat preferences have not been quantified. Our objectives were to assess: (1) abundance, (2) foraging behavior, (3) prey-capture methods, and (4) plant associations of Tufted Tit-Tyrants in semi-arid Matorral (shrublands) in north-central Chile. We made observations in summer and winter, and compared our results with predictions from Fitzpatrick's (1981) models of search strategies in tyrant flycatchers.

METHODS

We conducted our studies in the Quebrada de las Vacas, an interior valley in Parque Nacional Bosque de Fray Jorge ("Fray Jorge"). Fray Jorge comprises 9,959 ha on the coast of Chile's IV Region, 400 km north of Santiago and 100 km south of La Serena (30[degrees] 41' N, 71[degrees] 40' W) (Fig. 1). The habitat is coastal steppe Matorral (Gajardo 1993), characterized by dense (50-60%) ground cover of drought-resistant shrubs (Gutierrez et al. 1993). We focused our efforts in and around a long-term research station established to monitor ecological responses to abiotic influences (Meserve et al. 2003, Kelt et al. 2004). Avian inventories began with initial surveys in 2002 followed by quantitative studies of avian populations beginning in 2004. We visited our field site twice annually for this study and gathered foraging observations during three trips: 20-28 February 2002, 21-28 February 2004, and 28 July-10 August 2006. Observations were made by both authors. The avian study site is centered on the field station and comprises a series of eight transects spanning 6.5 km of Matorral habitat in Fray Jorge.

We quantified the behavior of actively foraging adult Tufted Tit-Tyrants and not those resting, primarily singing, or involved in other activities that might affect foraging behavior. Observations were conducted from 0700 to 1100 hrs under conditions of negligible wind. We regularly and repeatedly traversed the study site. Once a bird was found, we recorded sequential behaviors with a hand-held stopwatch. Initially, we did not record the first behavior observed, as this typically was the behavior that cued us to the bird, potentially introducing bias to our data (Franzeb 1984, Noon and Block 1990). We tracked the bird as long as we could record behavior. If the bird was lost (usually due...

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