Introduction:

Study of temporal variation of bird assemblages may be particularly important in highly dynamic ecosystems as fluvial wetlands to identify the factors that influence and contribute to maintain regional bird diversity.

Objective:

To study temporal variation in regional bird species composition (i.e. set of species that make up the assemblage) and richness (i.e. species number) and the factors that drive it, and quantify the importance of temporal-beta diversity to sustain bird regional diversity, in the fluvial system of the Middle Paraná River in Argentina.

Methods:

We sampled birds on a regional scale by performing 16 repeated surveys roughly every 45 days across 2 years (2011-2013) at 60 point counts distributed along the fluvial system.

Results:

We recorded a total of 162 species and 12 738 detections, with a mean of 72.7 ± 1.9 species and 796.1 ± 41 individuals per survey. Temporal beta diversity accounted for 57 % of regional bird species richness. Bird composition varied seasonally because of the species turnover (and not nestedness) between non-breeding and breeding periods; migrant species contributed to this issue but did not account for all these differences. Difference in bird composition between years was associated primarily to species turnover within non-breeding periods and was related to changes in water levels. Temporal variation in availability of habitats across the regional extent of the fluvial system accounted for the highest proportion of temporal beta diversity. Species richness neither varies seasonally nor was it related to fluctuations in water level or habitats.

Conclusions:

The climatic seasonality and environmental dynamics of the fluvial system, as a function of water-level fluctuations and of variations in habitat availability, jointly influence regional composition of birds through temporal species turnover. These variations in regional composition were not related to variations in regional species richness. These results show the importance of the natural dynamic of the fluvial system to preserve the processes that maintain the regional assemblage of birds.