The potential role of waterbirds in dispersing invertebrates and plants in arid Australia

Abstract

1. The role of waterbirds as vectors of plants and invertebrates within and between arid-zone wetlands is poorly understood. We present the first detailed study of passive dispersal by nomadic birds in Australasia. We investigated the numbers and types of invertebrate and plant propagules within freshly collected faecal samples as well as their viability. We compared dispersal among Grey Teal ('Anas gracilis'), Eurasian Coot ('Fulica atra') and Black Swan ('Cygnus atratus') in the Macquarie Marshes, a complex of temporary to semi-permanent wetlands in New South Wales. 2. When faecal samples (n = 60) were inundated in the laboratory and monitored over 3 weeks, ciliates (75% of samples), nematodes (22%), ostracods (13%) and rotifers (5%) were recorded, with higher taxon richness in coot samples. Faecal samples (n = 71) were also sieved to quantify intact propagules, and ostracod eggs (70% of samples), large branchiopod eggs (31%) and bryozoan statoblasts (31%) were the most abundant invertebrates. Diaspores of 19 plant taxa were recorded, 14 of which were germinated in the laboratory or shown to be viable at the end of germination trials. The abundance and diversity of invertebrate propagules was highest in coot samples, whereas the abundance and diversity of diaspores was highest in teal samples. 3. One Australian Pelican ('Pelecanus conspicillatus') sample was obtained and found to contain more taxa and far more propagules than any sample from other waterbirds, suggesting that piscivorous birds might have an important role in the indirect dispersal of propagules ingested by fish. 4. Our results support a role for birds in explaining the distributions of cosmopolitan plant genera such as 'Lemna', 'Typha', 'Myriophyllum' and 'Nitella'. The alien plants 'Ranunculus sceleratus', 'Medicago polymorpha' and 'Polygonum arenastrum' were recorded, demonstrating the potential role of waterfowl in the spread of exotic species. As the frequency and duration of flooding of arid-zone wetlands decreases owing to human activities, the importance of waterbirds in facilitating recolonisation of temporary wetlands is likely to increase.