Wetland- and waterbirds were counted, mostly from vehicles, on 3400 hectares of the low-lying floodplains of the Incomati Delta, the Macaneta wetlands between January 2021 to February 2023. Over 300 bird species have been observed in and around these wetlands of which 153 species were considered wetland- and waterbirds, yielding a total of 61089 birds from 92 counts (664 birds per count). The counted area was divided into 21 zones according to altitude Above Mean Sea Level (all are below 4m AMSL) and vegetation characteristics. but not all zones could be accessed at each count (average 15.4 zones per count) resulting in a total of 1415 zones counted. Average duration of the counts was 3hrs 30min and covered 25 km of road. The counts were converted to monthly average biomass per countplot using average weight for each individual species. The species were divided into 10 feeding guilds on the basis of feeding spectrum from literature sources. Piscivores and herbivores were the dominant guilds, followed by aquatic invertebrate feeders, a specialized molluscivore, etc. The data were analysed using principal component analysis with the environmental variables collected: river discharge, salinity (monthly average per countplot), peak tide within 72 hours prior to the count, local rainfall (monthly total), altitude and vegetation type. In February 2021, almost the entire floodplain was covered by a >1000 m3s-1 river flood while 2022 was characterized by an exceptionally strong and extended rainy season. Both piscivore and raptor biomass correlated with river discharge 7 months prior to the counts, indicating a positive impact of flooding on floodplain productivity. As waterbird biomass, and in particular the piscivores, can be considered a proxy for fish and crustacean production these correlate with human well-being as fisheries are an important livelihood component in the delta, Maputo Bay and adjacent coastal waters. Maintaining such floodpeaks is thus essential for maintaining and enhancing the livelihoods of the vulnerable users of the area. In addition, it is suggested that managed flood releases prior to the equinox tides of September would be beneficial to both biodiversity values and ecosystem services of the delta, including by preventing high salinities destroying floodplain vegetation and thus increasing the risk of erosion.

Project funded by IRD, FFEM, IDRC Canada, GEF, UNEP, Nairobi Convention