Preliminary investigation of nocturnal habitat use by migratory waders (Order Charadriformes) in northern New South Wales

Abstract

Nocturnal and diurnal habitat use by migrant waders was studied at three sites in the Richmond estuary, northern New South Wales. Numerous species of migrant wader showed significant differences in habitat use between night and day. Sanderling (Calidris alba), red-necked stint (Calidris ruficollis) and, possibly, double-banded plover (Charadrius bicinctus) foraged on mudflats during the day but moved to ocean beaches to forage during night low tides. Pacific golden plover (Pluvialis fulva), greater sandplover (Charadrius leschenaultii), eastern curlew (Numenius madagascariensis) and bar-tailed godwit (Limosa lapponica) displayed less significant differences in habitat use, although densities increased at night on moist sandy mudflats. The numbers of terek sandpiper (Xenus cinereus) and curlew sandpiper (Calidris ferruginea) decreased on sandy mudflats at night although where these birds went is unknown. Nocturnal foraging by X. cinereus may be restricted to moonlit nights. Greenshank (Tringa nebularia) also displayed differences in habitat use by foraging more on moist sandy mud at night and less in sea grass. No significant differences were found for whimbrel (Numenius phaeopus). Habitat use by both N. madagascariensis and N. phaeopus appears related to lunar phase. Six hypotheses are postulated to explain the observed differences: (1) exploitation of changes in prey behaviour and availability; (2) predator avoidance; (3) human avoidance; (4) increased light on mudflats from urban areas; (5) avoidance of roosting flocks of gulls and terns; and (6) relationship with prevailing environmental conditions. The data presented provide a basis from which further work will be undertaken.