Differential responses to habitat structure and degradation by two Grassbirds (Fam. Locustellidae) syntopic in floodplain grassland

Abstract

AbstractWet grassland birds world-wide face mounting threats due to habitat destruction especially in the Indo-Gangetic foodplains, where in addition to intense human use, primarily for agriculture, there is a paucity of baseline information to inform conservation and management. We examined the response of two co-occurring foodplain grassland specialists, the globally threatened Bristled GrassbirdSchoenicola striatus(VU) and widespread but little-studied Striated GrassbirdMegalurus palustris(LC), to habitat structure and human use in foodplain grassland at two sites, one on the lower Ganges River and one on the Brahmaputra River, Bangladesh through point counts combined with vegetation surveys. Responses from the breeding seasons of 2018 and 2019 were assessed by linear models and bird densities estimated using distance sampling. Results indicate that the occurrence of Bristled Grassbird increased with homogeneous tall Saccharum grass cover but decreased with increased crop cover, which may be the main driver of its decline. Striated Grassbird showed a more generalized pattern of positive association with tall grassland vegetation including taller crops and exotic plants, but was also positively associated with grass harvesting indicating its avoidance of homogeneous tall grassland. Although the density of Striated Grassbirds at the Brahmaputra site was 3–4 times greater than that of Bristled Grassbird, it was nearly absent from the Ganges site, revealing previously unappreciated micro-habitat preferences. Comparison with a more common species provided a clearer understanding of habitat and human infuences on the more threatened grassbird. Long-term conservation of Bristled Grassbird requires careful management of grass harvesting and cattle grazing.