Resurrecting seasonal dynamics in waterbirds after wetland restoration: before-after monitoring highlights the role of a single dominant species.

Abstract

We compared a set of uni-varied diversity metrics of a guild of water-related birds (hereafter 'waterbirds') before and after a wetland restoration carried out on uncultivated (reclaimed) lands. Over a period of five years, we observed a restart of seasonal waterbirds dynamics after wetland restoration by flooding of abandoned croplands, with a significant increase in all metrics of diversity, more evident in autumn-winter periods. Seasonal thresholds were evident before (2017-2018) and after (2018-2019) the flooding. These dynamics appeared irregular, probably for a different inter-annual suitability of the flooded meadows due to local ecological factors (e.g., change in meteorological regime and in rush-bed vegetation cover). Rarefaction curves, both for richness and diversity, showed how the waterbird community moved towards a greater complexity. Flooded meadow restoration, particularly favoured wintering species in Mediterranean sites, which explained the strong fluctuations in total abundance. At the species level, Northern Lapwing (Vanellus vanellus), absent before restoration, was the most abundant species after flooding, using flooded meadows with its gregarious behaviour. This 'crowding' may be explained also for a lack of similar habitats in the surrounding. Other dominant species (Anas platyrhynchos, Ardea cinerea, Egretta garzetta) showed a significant increase after restoration. Standardized before-after monitoring on medium term time periods seem suitable to evidence inter-annual season dynamics in diversity metrics of waterbird assemblages.