Seasonal shift in the foraging niche of a tropical avian resident: resource competition at work?

Abstract

This study examined the foraging behaviour of a resident bird species, the rufous-capped warbler (RCWA, Basileuterus rufifrons), in a shaded-coffee farm in Chiapas, Mexico. Unlike many resident species that use shaded-coffee agroecosystems seasonally, RCWAs do not move to other habitats when migrants are present. RCWA foraging was compared when migrant birds were present (dry season) and absent (wet season). It was hypothesized that RCWAs would exhibit a seasonal foraging niche shift because of resource competition with migrants. Observations from both the canopy and coffee understorey show that RCWAs foraged almost equally in both vegetative layers during the wet season although they were more successful foraging in the canopy. In the dry season, migrants foraged primarily in the canopy and RCWAs shifted so that 80% of RCWA foraging manoeuvres were in the understorey. At that time RCWAs foraged less successfully in both vegetative layers. Avian predation in the dry season was found to reduce densities of arthropods by 47-79% in the canopy, as opposed to 4-5% in the understorey. In the canopy, availability of large (>5 mm in length) arthropods decreased by 58% from the wet to dry season. Such resource reductions could have caused the RCWA foraging niche shift yet other alternative or additional hypotheses are discussed. Shifts in foraging niche may be a widespread mechanism for some small insectivorous residents to avoid seasonal competition with abundant migrant species.Resumen: Este estudio examinó el comportamiento de forrajeo de un ave residente, Basileuterus rufifrons (RCWA), en una finca de café con sombra en Chiapas, México. A diferencia de muchas aves residentes que usan los agroecosistemas de café con sombra solamante durante una estación, RCWAs no se van a otros hábitats cuando los aves migrantes están presente. El forrajeo de RCWA fue comparado cuando las aves migrantes eran presente (laépoca seca) y ausente (lá epoca de lluvia). La hipótesis fue que los RCWA exhibirían un cambio de forrajeo con los cambios de estaciones a causa de la competencia de recursos con los migrantes. Observaciones en el docel y el sotobosque en un cafetal muestran que durante laépoca de lluvia, los RCWAs forrajean igualmente en los dos niveles de vegetación, pero tienen máś exito forrajeando en el docel. Durante laépoca seca, los migrantes forrajean principalmente en el docel y los RCWAs se mueven al sotobosque donde efectúan 80% de las maniobras de forrajeo. Durante ese tiempo, los RCWAs tuvieron menoséxito forrajeando tanto en el docel como en el sotobosque. Durante laépoca seca el número de artrópodos bajó entre 47-79% en el docel y entre 4-5% en el sotobosque a causa de la depredación de las aves. En el docel, la disponibilidad de artrópodos grandes (>5 mm en longitud) bajó en un 58% de laépoca de lluvia a laépoca seca. Tales reducciones de recursos podrían causar el cambio de lugar a forrajeo observado en RCWA, pero otras explicaciones e hipótesis son discutidas. Pueden ser que este cambio de forrajeo sea comú...

Birds as Predators in Tropical Agroforestry Systems

“…Previous observations in shaded coffee farms suggest that arthropod and bird abundances are greater in the canopy rather than the crop layer (Wunderle and Latta 1996, Greenberg et al 1997, Jedlicka et al 2006. We compared bird predation in the canopy and crop layers for three agroforestry studies (Table 1) in Mexico (Philpott et al 2004, Perfecto et al 2007) and in FIG. 1.…”

Simplification of a coffee foliage-dwelling beetle community under low-shade management

“…At one of our study sites, Philpott et al (2004) demonstrated that flying vertebrates depress the abundance of arthropods, including beetles, on branches of Inga shade trees. Jedlicka et al (2006) combined flying vertebrate exclosures in Inga shade trees with a subset of our exclosures in coffee at one of our study sites to show that flying vertebrates significantly depress the abundance of both large (45 mm) and small (o5 mm) arthropods in Inga foliage of the canopy, but not in the coffee foliage of the understory. However, Perfecto et al (2004) demonstrated increased removal rates of lepidopteran larvae, presumably by flying vertebrates, from coffee foliage outside of flying vertebrate exclosures in one of our high-shade sites.…”

“…Previous studies have suggested that birds and/or bats can significantly depress the abundance of arthropods on the foliage of Inga shade trees in coffee plantations (Philpott et al, 2004), or on the foliage of the coffee bushes, themselves (Greenberg, Bichier, Cruz-Ango´n, MacVean, & Perez et al, 2000;Perfecto et al, 2004). Jedlicka, Greenberg, Perfecto, Philpott, and Dietsch (2006) found that flying vertebrates depressed arthropod abundance in the canopy of Inga shade trees but not in the coffee bushes of the understory. Herein, we add to this emerging picture of top-down effects in coffee agroecosystems by analyzing the effects of flying vertebrate exclusion on the abundance, species richness, and species composition of beetles on coffee foliage.…”

Nitrogen preferences and plant-soil feedbacks as influenced by neighbors in the alpine tundra

“…Resource utilization patterns could also reflect past adaptations to competitive interactions (Connell 1980) or the importance of facilitative interactions (Bertness and Callaway 1994). To date, there have been few empirical tests of the competitive mechanism assumed by niche models (Silvertown 2004), and the few that have been conducted have yielded conflicting results (Hairston 1980a, b;Jedlicka et al 2006;Miller et al 2007;Pacala and Roughgarden 1982;Thomson 2006).…”