The agricultural landscapes of India are filled with numerous wetlands that cater to multiple human needs such as irrigation, cattle grazing and fish harvest. These wetlands also provide crucial habitats for many resident and migratory bird species. Most of these wetlands are not protected under law, and bird conservation and management attempts are restricted only to large wetlands (e.g. Ramsar sites). The reasoning behind this approach is that large wetlands are likely to include all the species that smaller wetlands contain, and more, and therefore focusing on large wetlands gives ‘the biggest bang’ for the sparse conservation bucks. A recent study conducted by Sundar and Kittur in the cereal growing landscapes of north India questions this notion by showing that a landscape approach to bird conservation, where wetlands of various sizes occurring at varied densities are managed, in fact maximises returns on biodiversity conservation.

Wetlands of all sizes crucial for maintaining water bird diversity in agrarian landscapes

Deepthi Chimalakonda

The study tested whether large wetlands contain all species that are found in smaller wetlands. In other words, are species of smaller wetlands only subsets of the larger ones? Is this ‘nested pattern’, where smaller wetlands hold no unique species, dominant in this landscape?  If yes, managing only the large wetlands will be an efficient way to maximise conservation returns. On the contrary, if bird assemblages differ significantly among the wetlands, i.e. there is high ‘species turnover’ from one wetland to another, then a strategy that aims to find the best mix of small and large wetlands to conserve will be more effective.

Sundar and Kittur demonstrate that species richness of birds in agricultural wetlands is almost entirely maintained by species turnover rather than nestedness. Approximately 50% of the species in the landscape occurred only in one or two wetlands each. Species among the wetlands differ significantly and smaller wetlands contain species that are not found in larger ones.  At the same time, the study also showed that (IUCN classified) Near Threatened species such as the Oriental Darter and the Black-headed Ibis and Vulnerable species like the Sarus Crane preferred wetlands whose size is greater than the mean wetland size.  These results taken together strongly suggest that while larger wetlands are important for certain species of conservation importance, the smaller wetlands are equally important for maintaining species richness across the landscape.

Sundar K and S Kittur. 2013. Can wetlands maintained for human use also help conserve biodiversity? Landscape-scale patterns of bird use of wetlands in an agricultural landscape in north India. Biological Conservation 168:49-56.

Deepthi Chimalakonda is a research assistant at the Ecological Modelling and Economics Lab, National University of Singapore, Singapore, diptibharadwaj.l@gmail.com.