Dietary habits of the black-necked swan Cygnus melancoryphus(Birds: Anatidae) and variability of the aquatic macrophyte cover in the Río Cruces wetland, southern Chile.

Patricio Camus,Carlos Velásquez,Fabio Labra,Eduardo Jaramillo,Cristina San Martín,Maura (Gee) Geraldine Chapman

doi:10.1371/journal.pone.0226331

Abstract

The black-necked swan Cygnus melancoryphus is an aquatic herbivorous bird whose dietary habits depend on the dominance and accessibility of macrophyte banks in shallow areas of coastal and limnetic wetlands in southern South America. The swans from the Río Cruces wetland in southern Chile (ca. 39°S) feed mainly on the macrophyte Egeria densa from the water column between depths from less than 0,5 and 2,0 m. A micro- histological analysis of black-necked swan feces (N = 152) collected during six sampling occasions between 2012 and 2017 confirms the preferred consumption of E. densa and highlights the impact of temporal changes in the cover of these macrophytes on the swan’s diet. The dietary composition of black-necked swans appears as a reliable proxy for temporal changes in the distribution of the most common aquatic macrophytes in the Río Cruces wetland. These results highlight the importance of preserving shallow wetlands as the habitat for aquatic macrophytes that provide the main food source for these herbivorous water birds.

Highlights

Swans are among the largest existing flying birds of the waterfowl family Anatidae
Myriophyllum aquaticum and Schoenoplectus californicus were registered on four sampling dates, whereas Limnobium laevigatum was documented on three sampling dates (Table 1)
Even though our sampling strategy did not continuously cover the entire period from 2012 to 2017, the results suggest that the composition of the swan’s diet and the relative importance of the dietary items remained similar over the entire period and marked by an increasing dominance of E. densa

Summary

Introduction

Swans are among the largest existing flying birds of the waterfowl family Anatidae. They are represented around the world (except in Africa and Antarctica) by six species from the genus Cygnus: four in the temperate and artic zones of North America and Eurasia (Cygnus olor, Cygnus buccinator, Cygnus cygnus and Cygnus columbianus), one in the temperate zones of South America (Cygnus melancoryphus) and another one in the south of Australia and New Zealand (Cygnus atratus) [1,2]. Environmental aspects related to swans have triggered numerous conservation strategies around the world, for example the successful re-introduction of the trumpeter swan C. buccinator by wildlife American agencies after it was close to extinction during.

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Conclusion