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Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. [...]

Many migratory birds use staging sites to gain essential resources to fuel their ongoing migration. Understanding staging strategies reveals much about migration systems and is essential if one is concerned with monitoring population trends and mass gains, two of the principal methods for assessing the 'health' of a migratory population. In spring 2004, we investigated the staging behavior in Delaware Bay of Red Knot (Calidris canutus) using mark--recapture techniques and resightings of birds marked in the preceding spring. Individuals staged for 11-12 days, which declined to 8-10 days late in the season. Arrivals were asynchronous, but departures tended to be synchronized. A simple sensitivity analysis showed that the mark-recapture analysis estimated length of stay to within +10% and confirmed biases in monitoring trends and mass gains using peak counts and mass-on-date regressions. Alternative methods using staging duration to estimate passage population size and mass gains were shown to be unbiased. Using these methods, we estimated a passage population size in 2004 of 18,000 Red Knot that arrived at an average mass of 111 g and, on average, gained mass at 7.2 g [day.sup.-1]. Thus, in 2004, the passage population was substantially smaller than the recent peak count of 50,360 in 1998, which confirms a significant decline in the number of Red Knot staging in Delaware Bay. Use of refined techniques such as these is essential if management decisions such as those in Delaware Bay are to be based on firm scientific advice. Key words: Calidris canutus, Delaware Bay, mark-recapture models, mass gain, passage population size, Red Knot, staging ecology, turnover.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.07.001 Byline: Robin M. Fuller (a), Bernard J. Devereux (a), Simon Gillings (b), Ross A. Hill (c), Gabriel S. Amable (a) Keywords: Bird; Habitat; Map; Remote sensing; Biodiversity; Landscape; Ecology; Modelling Abstract: This paper develops a comprehensive and objective picture of bird distributions relative to habitats across Britain. Bird species presence/absence data from an extensive field survey and habitat data from the remotely sensed UK Land Cover Map 2000 were analysed in 36,920 tetrads (2kmx2km) across Britain (a 65% sample of Britain's c. 240000km.sup.2). Cluster analysis linked birds to generalised landscapes based on distinctive habitat assemblages. Maps of the clusters showed strong regional patterns associated with the habitat assemblages. Cluster centroid coordinates for each bird species and each habitat were combined across clusters to derive individualised bird-habitat preference indices and examine the importance of individual habitats for each bird species. Even rare species and scarce habitats showed successful linkages. Results were assessed against published accounts of bird-habitat relations. Objective corroboration strongly supported the associations. Relatively scarce coastal and wetland habitats proved particularly important for many birds. However, extensive arable farmland and woodland habitats were also favoured by many species, despite reported declines in bird numbers in these habitats. The fact that habitat-specialists do not or cannot move habitat is perhaps a reason for declining numbers where habitats have become unsuitable. This study showed that there are unifying principles determining bird-habitat relations which apply and can be quantified at the national scale, and which corroborate and complement the cumulative knowledge of many and varied surveys and ecological studies. This 'generality' suggests that we may be able, reliably and objectively, to integrate and scale up such disparate studies to the national scale, using this generalised framework. It also suggests the potential for a landscape ecology approach to bird-habitat analyses. Such developments will be important steps in building models to develop and test the sustainable management of landscapes for birds. Author Affiliation: (a) University of Cambridge, Unit for Landscape Modelling, Sir William Hardy Building, Downing Site, Tennis Court Road, Cambridge CB2 1QB, UK (b) British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK (c) Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK Article History: Received 6 July 2005; Revised 8 May 2006; Accepted 12 July 2006

Many species, including shorebirds, feed during both day and night, yet little is known about how this affects behavior and habitat preferences. European Golden-Plovers (Pluvialis apricaria) and Northern Lapwings (Vanellus vanellus) feeding on arable farmland were more widely dispersed at night: nocturnal flocks were smaller, typically monospecific, and occurred in many more fields than diurnal mixed-species flocks. Diurnal numbers of European Golden-Plovers could not be used to predict nocturnal numbers; this indicates that ranging behavior differed between day and night. For both species, nocturnal feeding was recorded on almost all nights, irrespective of moon phase. Northern Lapwing nocturnal feeding activity decreased with increasing cloud cover and decreasing ground temperature, but no clear relationships were detected between European Golden-Plovers' nocturnal feeding activity and environmental variables. Habitat selection differed between day and night, and between species at night. Diurnal studies of habitat choice and site selection may misrepresent the full requirements of such species. Received 20 April 2004, accepted 8 April 2005. Key words: European Golden-Plover, habitat selection, nocturnal, Northern Lapwing, Pluvialis apricaria, Vanellus vanellus.