Day-night activity of intertidal invertebrates and methods to estimate prey accessibility for shorebirds

Abstract

EssER, W., VOGE, S. & Exo, K.-M. (2008): Day-night activity of intertidal invertebrates and methods to estimate prey accessibility for shorebirds. -Senckenbergiana maritima, 38 (2): 115-122, 5 Figs., 1 Tab., Frankfurt am Main]Investigations of day and night abundance and foraging activity of several shorebird and waterfowl species in the western Jade Bay had previously shown that their abundance did not differ between day and night but the proportion actively foraging was significantly higher at night, especially in surface feeders, such as plovers, Dunlins, Common Redshanks, Pied Avocets, Shelducks and Mallards. Foraging activity patterns in shorebirds are greatly affected by the behaviour and availability of their benthic prey, but quantitative data on day-night activity of intertidal invertebrates are scarce. ~lherefore in this study we determined activity patterns and availability of benthic prey species (i) by different sampling methods and (ii) by visual observations of macrozoobenthic organisms during day and night from April to June 2004. Sampling showed that the abundance and biomass of macrozoobenthic organisms was similar during both day and night. But visual observations showed significantly greater numbers of the polychaetes Hediste diversicalor and Heteromastusflliformis at the surface by night than by day suggesting that polychaetes may be more available to shorebirds at night. In addition two sampling methods, the generally used corer and the sediment-plane (described by DESHOLM et al. 1998) were compared for their ability to determine the vertical distribution of benthic organisms. Sediment-plane samples showed a significantly higher abundance of vertically mobile polychaetes in the uppermost layer than the core samples, qhis indicates that the sediment-plane is a better and more accurate means of recording the density of benthos communities in the uppermost sediment layers than the corer, because the poiychaetes are not able to escape into deeper mud. However, the best method for determining the availability of macrozoobenthic prey for surface feeding birds would appear to be direct observation of surface activity.

Nycthemeral Movements of Wintering Shorebirds Reveal Important Differences in Habitat Uses of Feeding Areas and Roosts

“…This could be related to the dominance of polychaetes, more active and likely more available at night (Last and Olive 2004;Kuwae 2007) in habitats A2.32 and A2.231, which could explain the nocturnal use of these habitats by godwits. We did not have available data to compare diurnal and nocturnal prey density, but studies underlined that polychaete worms, the favored preys of bar-tailed godwits (Duijns et al 2013), may be closer to the sediment surface at night (McNeil et al 1992;Esser et al 2008). Such a density of prey available in the top layer of the sediment could explain the nocturnal preference of polychaetedominated habitats by godwits, as observed in dunlins and redshanks (Mouritsen 1994;Burton and Armitage 2005).…”

“…Sight-feeding shorebirds could also benefit from night feeding because of the moonlight (McNeil et al 1992) and/or physiological adaptations improving their nocturnal vision (Pienkowski 1983;Rojas et al 1999) to maintain a high intake rate during nighttime (Pienkowski 1983;Lourenço et al 2008). Furthermore, the higher activity and accessibility of prey at night in intertidal mudflats (McNeil et al 1995;Esser et al 2008), combined with the aforementioned bird capacities, could explain such an interest in nocturnal foraging behavior to satisfy wintering energetic requirements.…”

Macrofauna succession in an infilling salt marsh clay pit

“…The early successional stages were characterized by the recruitment of marine pioneer species such as H. diversicolor, H. filiformis, P. l#oralis and H. ulvae, which occurred in high abundances. In turn,/-L diversicolor is an important food source for birds (R~IsE 1985, ESSER et al 2008. The polychaete H. diversicolor disperses by planktic larvae and is abundant in the upper parts of the intertidal (estuarine, mud flat and salt marsh habitats) worldwide (HARXMANN-ScHR6DER 1996).…”

“…it is an important food source for birds (HIDDINK et al 2002, ESSER et al 2008. The current high demand of soil material (day) for dike construction and maintenance along the mainland coastline of Lower Saxony leads to major disturbance of the salt marsh ecosystem and consequently to changes in the macrofauna species composition, abundance or biomass.…”