Avian Community Responses to Variability in River Hydrology

Abstract

River flow is a major driver of morphological structure and community dynamics in riverine-floodplain ecosystems. Flow influences in-stream communities through changes in water velocity, depth, temperature, turbidity and nutrient fluxes, and perturbations in the organisation of lower trophic levels are cascaded through the food web, resulting in shifts in food availability for consumer species. River birds are sensitive to spatial and phenological mismatches with aquatic prey following flow disturbances; however, the role of flow as a determinant of riparian ecological structure remains poorly known. This knowledge is crucial to help to predict if, and how, riparian communities will be influenced by climate-induced changes in river flow characterised by more extreme high (i.e. flood) and/or low (i.e. drought) flow events. Here, we combine national-scale datasets of river bird surveys and river flow archives to understand how hydrological disturbance has affected the distribution of riparian species at higher trophic levels. Data were analysed for 71 river locations using a Generalized Additive Model framework and a model averaging procedure. Species had complex but biologically interpretable associations with hydrological indices, with species’ responses consistent with their ecology, indicating that hydrological-disturbance has implications for higher trophic levels in riparian food webs. Our quantitative analysis of river flow-bird relationships demonstrates the potential vulnerability of riparian species to the impacts of changing flow variability and represents an important contribution in helping to understand how bird communities might respond to a climate change-induced increase in the intensity of floods and droughts. Moreover, the success in relating parameters of river flow variability to species’ distributions highlights the need to include river flow data in climate change impact models of species’ distributions.

Shared environmental responses drive co‐occurrence patterns in river bird communities

“…Description of the four environmental variables used in the joint species distribution model (JSDM) as predictors of the occurrence and co-occurrence patterns of 19 river bird species across mainland Great Britain. River flow variables were defined a priori according to Royan et al (2013) and were calculated using long-term averages between 1998 and 2011 (inclusive) with data obtained from the National River Flow Archive (NRFA). Land use data were produced by the Centre for Ecology and Hydrology (CEH) as part of the Countryside Survey 2000 and were derived from the satellite-generated Land Cover Map 2000 (LCM2000) with a resolution of 50 m. Climate data were obtained from the UKCP09 gridded observation datasets at 5  5 km resolution at monthly timescales and climate variables were calculated using data between January 1998 and December 2011 (inclusive).…”

Climate‐induced changes in river flow regimes will alter future bird distributions

“…Therefore, we identified a priori model parameters that characterize key facets of the hydrological regime on rivers in Great Britain (e.g., variation in flow magnitude, frequency, and duration). In Royan et al 2013, the importance of river flow predictor variables in describing Dipper distribution was tested using a model averaging approach, comparing the performance of 31 plausible model structures. Here we constructed our models using the four hydrological variables (Table 1) that best characterized Dipper distribution in Royan et al 2013.…”

“…In Royan et al 2013, the importance of river flow predictor variables in describing Dipper distribution was tested using a model averaging approach, comparing the performance of 31 plausible model structures. Here we constructed our models using the four hydrological variables (Table 1) that best characterized Dipper distribution in Royan et al 2013. These variables capture variability around flow magnitude, frequency, and duration around both high and low flows, which are predicted to be significantly altered as a result of climate change (Prudhomme et al 2012b).…”

“…Here we constructed our models using the four hydrological variables (Table 1) that best characterized Dipper distribution in Royan et al 2013. These variables capture variability around flow magnitude, frequency, and duration around both high and low flows, which are predicted to be significantly altered as a result of climate change (Prudhomme et al 2012b).…”

“…River birds are vulnerable to spatial and phenological mismatches with prey caused by shifting flows, as both species distribution (Royan et al 2013) and abundance (Royan et al 2014) are closely linked to variability around high (flood) and low (drought) flow conditions. High flows reduce river bird prey abundance and biomass, such as aquatic macroinvertebrates (Chiu et al 2013), impacting, in turn, on the timing and location of avian foraging (Cumming et al 2012), territory occupancy (Reiley et al 2013), and survival and breeding success (Strasevicius et al 2013).…”