1. 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.
2. 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.
3. 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.
4. 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.

Study area

We conducted the study around a 218.8 km² reservoir created by a dam in the São Marcos river (18^o 02’ 43.16” S, 47^o 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 sensu stricto”), 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).

Bird surveys

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).