Spatial analysis of sap consumption by birds in the Chaco dry forests from Argentina

Abstract

Sap is a resource of high energy content that is usually inaccessible to birds, although woodpeckers have the ability to drill into living trees to obtain sap. Because spatial patterns of resource availability influence avian abundance, we explored how spatial patterns of sap availability determine the spatial distribution of two sap-feeding species in the semiarid Chaco of Argentina. We studied the White-fronted Woodpecker (Melanerpes cactorum), which obtains sap by drilling holes into tree trunks, and the Glittering-bellied Emerald (Chlorostilbon aureoventris), which can obtain sap only from active woodpecker holes; 12 other bird species also exploited the sap flows from holes drilled by White-fronted Woodpeckers. The abundance of tree species used for sap feeding did not explain the spatial patterns of territorial groups of White-fronted Woodpeckers. However, within each territory, the abundance of Woodpeckers was centred on a single tree from which sap was obtained. The abundance of the Emeralds was strongly associated with the availability of trees with active sap-holes. During the dry season, sap is a major component in the diet of White-fronted Woodpeckers and Glittering-bellied Emeralds. However, the spatial distribution of these two consumers in relation to the availability of sap was species-specific. This species-specific response was closely related to the ecology and life history of each species. The abundance of woodpeckers could be determined by local mechanisms, such as location of a single sap tree in their small territories, whereas non-territorial hummingbirds would be able to track sap wells at a larger scale than the territory of a single territorial group of Woodpeckers. Our results show the importance of spatial analysis in identifying the ecological determinant of habitat selection and niche differentiation within species.

Biología del Cortarramas (Phytotoma r. rutila) en el departamento Gral. San Martín, Córdoba, Argentina

“…El Cortarramas se alimenta principalmente de hojas y también de frutos, flores y hasta savia (Martínez et al 1975, Masramón 1984, Bucher et al 2003, de la Peña & Pensiero 2003, de la Peña 2010, Macchi et al 2011. Bucher et al (2003) encontraron que la dieta estuvo compuesta en un 91 % por hojas de plantas dicotiledóneas en Córdoba.…”

Sap Consumption by the White-fronted Woodpecker and Its Role in Avian Assemblage Structure in Dry Forests

“…In nectarivorous species, seasonality in sap feeding seems to be controlled by the availability of nectar, with birds using sap in periods of flower shortage (Macchi et al 2011). Because nectar and sap are similar resources in terms of energy and nutritional characteristics, the sugars present in the sap provide occasional nectarivores with the energy they need at critical periods (Cecere et al 2011).…”

“…We also investigated (2) sap consumption by other birds that use the woodpecker's sap wells, seasonality in their use of this resource, and their capacity to assimilate sucrose as a functional factor determining this interaction. Both specialist and facultative nectar-feeding birds (e.g., hummingbirds and orioles, respectively; Macchi et al 2011) assimilate sucrose efficiently (Nicolson and Fleming 2003), so we expect these species to consume sap more frequently than other species during periods of scarce resources. (3) Finally, we evaluated aggressive interactions between the White-fronted Woodpecker and other species that approach sap wells to feed on sap flows.…”

“…months of low productivity (Blendinger 1999), which coincide with autumn (May-June) and winter (July-August), when the availability of arthropods, flowers, and fruits declines (Caziani 1996, Codesido andBilenca 2004). Fifteen species of birds, diverse in ecological attributes and taxonomic affinities, have been reported to feed on sap from wells in arid and semiarid environments in western Argentina (Genise et al 1993, Blendinger 1999, including species as highly dependent on energy-rich resources as the Glittering-bellied Emerald (Chlorostilbon aureoventris), which closely tracks trees with active wells (Macchi et al 2011). …”

“…At Rivadavia Banda Sur, the Whitefronted Woodpecker lives in flocks that maintain permanent territories, in which all the individuals feed together and cooperate in territorial defense and care of nestlings (Macchi et al 2011). We identified 10 groups of White-fronted Woodpeckers and delimited their territories; for that purpose, we mist-netted and color-banded the birds.…”