Assessing the habitat suitability of paddy fields for avian indicators based on hydropedological parameters of the wet agricultural soil along the Cauvery delta basin, India

Abstract

Paddy fields provide a broad range of habitats to wintering waterbirds as natural wetlands have declined worldwide. However, the intensification of farming practices has altered the microclimates of the wet agricultural soil, the composition of soil invertebrates, thus indirectly affecting the avifauna. This study evaluated the importance of paddy fields as wintering grounds for two avian indicators Asian openbill stork (Anastomus oscitans), and the Black-headed ibis (Threskiornis melanocephalus) along the Cauvery delta basin, widely known as the granary of Tamil Nadu, South India. Several stretches of this agricultural belt have recorded a drastic reduction in crop cover thereby threatening the species that forage these mosaics. This entire delta region is under threat and is increasingly shrinking due to indiscriminate sand mining activities causing irreparable damage to soil, fauna, and agriculture. The erratic monsoons have forced wading species to initiate long migrations in response to climatic adaptations, thus impairing the existing population. The present study focused on the abundance patterns of two wading birds and their association with the hydropedological parameters of the flooded soil along the deltaic dynamic mosaic. The relative abundance of the avifauna was documented for 24 months using unlimited radius point counts. The hydropedological parameters recorded were pH, electrical conductivity, total alkalinity, calcium carbonate, organic matter, total organic carbon, nitrogen, phosphorus, potassium, chloride, sodium, magnesium, calcium, sulfur, moisture, the particle size distribution of sand, silt and clay, water holding capacity, and bulk density. The results indicate that paddy fields are excellent habitat for A. oscitans and T. melanocephalus and are strongly influenced by landscape characteristics, availability of feeding grounds, and hydropedological parameters of the wet soil. Among the hydropedological parameters, organic matter and nitrogen exhibited a negative correlation and the percent silt content showed a positive correlation to A. oscitans. Similarly, T. melanocephalus showed a negative correlation to chloride and sodium, and a positive correlation to nitrogen. The contrasting effects of hydropedological parameters could be explained by differential thermal tolerance levels and metabolic requirements of the species or may be mediated by changes in the macrofaunal composition. The wet agricultural soil exhibited fewer differences across salinity classes, particle size distribution especially silt and clay, organic matter, total organic carbon, pH and bulk density, and greater differences among calcium content, water holding capacity, the particle size distribution of sand, and electrical conductivity across delta zones. Our study highlights the need to consider hydropedological factors of the wet paddy soil when selecting conservation sites on agro-landscapes for migratory wetland birds. Agricultural policies should aim at considering these cultural landscapes along the delta region...