DOI: 10.5061/dryad.j6q573n9f
title: River dams and the stability of bird communities: A hierarchical Bayesian analysis in a tropical hydroelectric power plant

description: The effects of anthropogenic disturbance upon the stability of wildlife
 communities depend on the heterogeneity and connectivity of habitat
 remnants on multiple scales. The number of hydroelectric dams in
 biodiversity hotspots (Africa, South America and Asia) is growing rapidly.
 To establish their environmental impact, it is essential to understand the
 dynamics of wildlife communities before and following the establishment of
 dams. We evaluated the impacts of the filling of the Serra do Facão
 hydroelectric reservoir in the São Marcos river, central Brazil, upon the
 bird community. Using data from 1,145 surveys across 20 sampling sites
 over eight years, two years before and six years after the filling of the
 reservoir, we assessed the resistance, i.e., maintenance close to an
 equilibrium state during the disturbance, and resilience, i.e., ability to
 return to the original state following the disturbance, of the bird
 community. We used spatiotemporal hierarchical Bayesian models to assess
 the effects of reservoir filling on five community parameters: abundance,
 richness, phylogenetic diversity, functional diversity and species
 composition. In the period subsequent to reservoir filling, there was (i)
 a marked reduction in bird abundance, richness, phylogenetic diversity and
 functional diversity, and (ii) a reduction in the proportion of forest
 species, coupled with an increase in the proportion of savanna species.
 Except for bird abundance, none of the other community attributes returned
 to their original levels, even after six years. Our findings indicate that
 Cerrado bird communities have both low resistance and low resilience to
 habitat loss associated with the establishment of hydroelectric
 reservoirs. Synthesis and applications. The environmental costs of
 hydroelectric dams are still underestimated or neglected in Brazil. A new
 paradigm in the assessment of their environmental impacts is warranted,
 incorporating (i) models of spatiotemporal variations based on long-term
 monitoring with surveys initiated before disturbances and (ii) measures of
 functional and phylogenetic diversity, such that society can understand
 the costs and benefits of the establishment of new hydroelectric dams and
 make informed decisions. Biodiversity loss could be minimized by ensuring
 the preservation and connectivity of alluvial habitats, capable of
 maintaining the supply of resources and the functional and phylogenetic
 attributes of bird communities associated with such habitats.
description: <b>Study
 area</b> We
 conducted the study around a 218.8 km<sup>2</sup> reservoir
 created by a dam in the São Marcos river (18<sup>o</sup> 02’
 43.16” S, 47<sup>o</sup> 40’ 32.29” W), between Goiás and
 Minas Gerais states, central Brazil (Fig. 1). The dam was built for the
 Serra do Facão hydroelectric power plant, with an installed capacity of
 212.6 MW, to support the mining industry in the region (Reinaldo &
 de Mesquita 2013). The São Marcos river belongs to the River Plate basin,
 the second largest watershed in South America, and is situated in the
 Cerrado biome, a global biodiversity hotspot (Myers et al. 2000). Because
 of the steep relief and pronounced slope towards the São Marcos river, few
 islands were formed in the reservoir. The climate is tropical with dry
 winter (Aw) in Köppen’s climate classification, characterized by an
 average annual temperature of 23.4 ºC, average annual precipitation of
 1,500 mm, and two well-defined seasons—a wet season from October to April,
 and a dry season from May to September (Alvares et al. 2013; Cardoso,
 Marcuzzo & Barros 2015). The vegetation consists of a mosaic of
 grasslands (“campo limpo”), shrubby grasslands (“campo sujo”), arboreal
 savannas (“cerrado <i>sensu stricto</i>”), and rocky
 scrublands (“campos rupestres”), generally located in plateaus and slopes,
 interspersed by gallery forests and dry forests (“mata seca”), which
 dominate in alluvial corridors (Ribeiro et al. 1998; Oliveira-Filho
 & Ratter 2002; Amorim et al. 2017).   <b>Bird surveys</b>
 We selected twelve sampling sites in
 forest, and another twelve in open habitats, separated by at least 1 km to
 ensure spatial independence (Fig. 1). The dam was completed in November
 2009 and the reservoir became functional in October 2010 (Reinaldo
 & de Mesquita 2013). Four forest sites were submerged with the
 filling of the reservoir (November 2009) and were surveyed only before
 that (F4, F5, F8 and F12; Table 1). We used the point count method,
 recording all birds seen or heard during 20 min, within a 50 m-radius
 circle (Bibby et al. 2000). We conducted surveys during peak bird activity
 times (06:00–10:00 and 16:00–19:00), from May 2008 until July 2015: 16
 trimestrial fieldtrips between May 2008 and February 2012, and six
 fieldtrips between February 2013 and July 2015, at irregular intervals
 (4–10 months). During each fieldtrip, we performed 2–9 surveys at each
 site (one observer), totalling 1,145 surveys and 22 fieldtrips. The
 variable number of surveys at each site resulted from our attempt to
 compensate for very cold or rainy days with increased sampling. At each
 sampling site, we spaced survey points by at least 200 m during the same
 fieldtrip. On the average, we performed 52 surveys/fieldtrip (37–88) and
 47.8 surveys/site (9–88) (Supporting Information Table S1).