Elsevier

Basic and Applied Ecology

Volume 49, December 2020, Pages 13-21
Basic and Applied Ecology

Bird community changes associated with cattle raising management in the delta forests of the Paraná River

https://doi.org/10.1016/j.baae.2020.09.011Get rights and content

Abstract

Riparian forests and environments close to watercourses support high biodiversity, which may be modified by human activities. In the Paraná River Delta region, cattle raising is one of the activities with the greatest impact, altering vegetation structure. These changes are reflected in bird communities that inhabit these environments. We hypothesize that the absence of large herbivores (whether cows or native deer) will produce an increase in the vegetation cover of the lower strata of forests, due to the greater height of the herbaceous stratum and greater coverage of the shrub stratum, and that these changes mainly affect the species of birds that use resources associated with these strata. Our objective was to understand the changes in richness and abundance of the bird community among different types of cattle management using a functional aggregation approach of bird species. In the areas with cattle, we found less coverage of the shrub layer, lower height of the herbaceous layer and fewer climbing vines. We found that changes in richness and abundance of bird community were strongly related to species associated with the lower vegetation strata (ground-feeding guild, shrub guild and low canopy guild), and that the responses of the different guilds were not homogeneous. Understanding the direction of changes in bird communities occurring in response to modifications of the environment, allows us to optimize conservation efforts. If these efforts are based on conservation of the environment in its natural state, we should adjust the management of the herbivory to the pristine conditions of the environment. On the other hand, if conservation efforts are based on particular species or groups of species associated with certain resources, the correct management of herbivory by cattle can be essential to obtain successful results.

Introduction

Riparian forests and environments close to watercourses support high biodiversity but most of these environments are subject to anthropogenic processes, such as fishing, hunting, house construction, and navigation, extraction of firewood and trees, and cattle raising (Berduc, Lorenzón, and Beltzer, 2015; Croonquist and Brooks, 1991, 1993; Kandus and Quintana 2016). The latter activity is considered one of the anthropogenic processes that changes the environment the most, because presence or absence of large herbivores like cows modifies vegetation structure (Jansen and Robertson 2001; McIntyre, Heard, and Martin, 2003; Quintana, Bó, Astrada, and Reeves, 2014). Spatial homogenization of the habitat is expected at very high cattle raising intensities, while low or moderate cattle raising levels may increase spatial heterogeneity of the habitat (Fuhlendorf and Engle 2001). This increase in spatial heterogeneity of the habitat is positively related to the overall diversity of bird species, both locally and at landscapes scales (Frutos, Reales, Lorenzón, and Ronchi-Virgolini, 2016; Penteado, Yamashita, Marques, and Verdade, 2016; Verdú, Crespo, and Galante, 2000).

Bird communities from around the planet have been reported to display differing responses to the presence or absence of cattle, and associated grazing pressures. For example, an Australian study has found with the majority of bird species declining with increasing grazing pressure (Martin and Possingham 2005). In the United States, bird response (negative or positive) may depended on the intensity of cattle raising (Fuhlendorf and Engle 2001). Similar results have been found in European regions (Laiolo, Dondero, Ciliento, and Rolando, 2004). On the other hand, other studies have found negative responses of bird communities in terms of density and richness after cattle had been excluded (García, Renison, Cingolani, and Fernández-Juricic, 2008). Apparently, the effect of cattle density on bird communities in the environment depends not only on the loads used, but also on the specific herbivory context of the region, possibly with a marked influence of the recent evolutionary processes of the environments in the presence or absence of large herbivores, and of the current populations of native herbivores (García et al., 2008; Kay et al., 2017; Okes, Hockey, and Cumming, 2008).

Different species of birds may respond differently to changes or disturbances in the environment, so some species may be favored or harmed, and others not altered (Okes et al., 2008; Rotenberry and Wiens 1980; Weller, 2003). The guild approach proposing supra-specific groups has been profusely applied in ornithological studies, as an alternative to the more complicated species-specific approaches (Bejarano et al., 2011; Croonquist and Brooks 1991; Farías, Marone, and Jaksic, 2007). Species classification into guilds according to resource use, facilitates bird community studies, allowing comparisons regarding functional organization of the guilds (Blondel, 2003; Gitay and Noble 1997; Terborgh and Robinson 1986; Wilson, 1999). This is a functional approach because for species with similar habitat uses and food requirements (similar ecological function), a similar response to spatial-temporal variation in the habitats is expected, allowing to examine differences that may not be observed at the species level or in the structure of bird communities.

We hypothesized that absence of large herbivores (cows) would result in an increase in vegetation cover of the lower strata of the riparian forest, with greater height of the herbaceous layer and a denser cover of the shrub stratum, and that these changes would mainly affect guilds that use resources associated with these strata. Our aim was to understand changes in richness and abundances of the bird communities under different types of cattle raising management in riparian forests of the Paraná River delta, using a functional guild approach of bird species.

Section snippets

Study area

The study was conducted in floodplain forests in the Pre-Delta region of the Paraná River, from Pre-Delta National Park (32° 03 ' S; 60° 38 ' W), south to Islas de Santa Fe National Park (32° 25 ' S; 60° 49 ' W), Argentina. The climate in the area is temperate/warm humid (Kottek, Grieser, Beck, Rudolf, and Rubel, 2006). Annual average temperature is about 19 °C and annual rainfall is ~900 mm, with warmer and rainier summer periods than in winter.

Sampling design

Data were collected in riparian forest under

Results

Canopy cover was similar among the types of management throughout the three years of sampling (Fig. 1A; see Appendix A: Table 1). In IwC, we found fewer climbing vines, compared to NC and RCE forests. Cortaderia selloana, a tall herb, was included in the shrub layer due to its large size. This was the most abundant species in the shrub stratum in IwC. The shrub stratum only showed greater coverage in RCE with respect to IwC although these differences were not constant during the entire sampling

Discussion

The ground-feeding guild presented the greatest differences with respect to type of cattle raising management, and in general, species that make up this guild were positively associated with IwC. The shrub guild presented the higher abundance values detected during cold seasons (autumn and winter) in NC and mainly in RCE may respond to a greater supply of food resources associated with the lower strata, with higher values of shrub cover in RCE, and little developed in IwC. The low canopy

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We appreciate the valuable contributions of the anonymous reviewers who have helped to improve our manuscript.

Funding statement

This study was funded by Consejo Nacional de Investigaciones Científicas y Técnicas, Agencia Nacional de Promoción Científica y Tecnológica (PICT Piña 2014), and Universidad Autónoma de Entre Ríos (PIDAC Piña 2015).

Ethics statement

This study complies with all Argentina laws and adheres to appropriate ethical standards.

Author contributions

A.E.F. and C.I.P conceived the project. A.E.F performed the data collection. A.E.F, P.M.L.L and C.I.P analyzed data and prepared the manuscript.

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