Pasture area and landscape heterogeneity are key determinants of bird diversity in intensively managed farmland

Abstract

Agriculture intensification has drastically altered farmland mosaics, while seminatural grasslands have been considerably reduced and fragmented. Bird declines in northern temperate latitudes are attributed to habitat loss and degradation in farmed landscapes. Conversely, landscape-modification effects on grassland/farmland bird communities are less studied in the South American temperate grasslands. We investigated how bird communities were influenced by landscape characteristics in the Rolling Pampa (Argentina). We sampled bird communities in 356 landscapes of 1-km radius that varied in cover and configuration of pastureland, flooding grassland and cropland. Using generalized linear models, we explored the relationship between both bird species richness and abundance, and landscape structure. Analyses were carried out for all species, and open-habitat, grassland and aquatic species. Pasture area was far the most important factor, followed by landscape composition, in predicting species richness and abundance, irrespective of specific habitat preferences, followed by partially-flooded grassland cover and its mean shape index. Grassland fragmentation did not affect species richness or abundance. When comparing the effects of landscape variables on bird richness and abundance (using mean model coefficients), pasture and grassland area effects were on average more than four times greater than those of compositional heterogeneity, and about ten times greater than shape effects. To conserve species-rich bird communities persisting in Rolling Pampa farmland, we recommend the A. Cerezo Á M. C. Conde

Landbird Assemblages in Different Agricultural Landscapes: A Case Study in the Pampas of Central Argentina

“…Many species detected in our study use roadside vegetation either for breeding or foraging (Szpeiner et al 2007, Di Giacomo and Lopez de Casenave 2010, Cerezo et al 2011. Additionally, within pastoral landscapes temporary wetlands support greater abundances of wetland specialists such as the White-faced Ibis (Plegadis chihi) and Cattle Egret (Bubulcus ibis), which forage in the these zones as well as in grassland (see also Canevari et al 1991, Codesido et al 2012.…”

“…In the pastoral landscapes, grasslands shelter the greatest number of nesting specialists because these grasslands most closely resemble the pre-settlement conditions of the Pampas (Cerezo et al 2011. Land used for cattle grazing (at low to moderate rates) can provide a wide range of opportunities for birds that forage on invertebrates and seeds (Perkins et al 2000), and pastures may offer the greater horizontal and vertical structural diversity that can support a greater abundance and diversity of grassland-breeding birds.…”

“…For instance, maintaining networks of roadside vegetation (e.g., undisturbed roadside vegetation or fence rows) may be crucial for promoting habitat complexity and biodiversity in intensively managed agricultural landscapes (Szpeiner et al 2007, Poggio et al 2010, Cerezo et al 2011). …”

“…Recent studies of the avifauna of central Argentina have shown that the population density of several species of birds decreased as the proportion of cropland in the landscape increased (Filloy and Bellocq 2007, Cerezo et al 2011. detected a reduction in distribution of grassland birds in association with land-use changes, in particular with the loss of grasslands and increase of crops.…”

“…The association between attributes of bird species and various agricultural landscapes has been well documented in other temperate-zone agroecosystems (Atkinson et al 2002, Murphy 2003, Askins et al 2007, Herzon and O'Hara 2007. In the Pampas, some studies have attempted to quantify similar associations but covered restricted geographic scales (Cerezo et al 2011) or considering specific groups (e.g., diurnal raptores, Pedrana et al 2008) only. However, no studies in the Pampas evaluated the associations between bird assemblages and various agricultural landscapes.…”