The distribution and habitat requirements of the banded rail (Rallus philippensis) in Nelson and Marlborough

Abstract

The distribution, habitat use, breeding biology and diet of the banded rail, Rallus philippensis assimilis, a secretive, mainly wetland dwelling rail, was studied in Nelson and Marlborough in an attempt to find explanations for its decline and discontinuous distribution in New Zealand. Banded rails were found in saltmarshes throughout Nelson and Marlborough, but not in freshwater wetlands. Their absence from some saltmarshes was related to vegetation and the availability of fresh water. It was estimated that there were approximately 99 breeding pairs of banded rails in Nelson and Marlborough. The habitat use of saltmarsh by banded rails was investigated at one saltmarsh in the Waimea Inlet. The relationship between the rate of accumulation of banded rail footprints in the mud and the time of day, vegetation and topography was investigated using linear regression. Banded rails were diurnal, and most active in the morning and evening. Their activity was greatest in the lower reaches of the saltmarsh and was correlated with the presence of a rush species, Juncus maritimus. Banded rails were found to be double brooded, they laid an average of 4.67 eggs per brood, which took 21.5 days to hatch. Banded rails suffered considerable losses during nesting from introduced mammalian predators, but had survived this predation for at least 50 years in parts of Nelson and Marlborough. The diet of banded rails was investigated by faecal and gut content analysis and was found to consist primarily of a crab and two species of snail. Seasonal changes in the diet were apparently related to seasonal changes in the availability of small crabs. The energy and handling times of the banded rail's main prey were measured and the seasonal changes in diet were found to be consistent with optimal foraging theory. The present distribution and past decline of banded rails in New Zealand appears consistent with banded rails being restricted to regions with large areas of saltmarsh by competition, predation and the destruction of freshwater wetlands.