Differential survival in adult Eurasian oystercatchers Haematopus ostralegus

I explored the fitness implications of individual and sex differences in foraging strategy in the Eurasian oystercatcher Haematopus ostralegus by monitoring the survival of individually colour-ringed birds of known sex and known feeding specialisation. Over the period of this study, adult female annual and overwinter survival was significantly lower than adult male survival. However, contrary to previous findings, no differences in survival were found between birds of different feeding specialisations. Lower female survival was not due to sex differences in feeding specialisation. Possible mechanisms for sex differences in survival and the survival implications of different feeding specialisations are discussed. I conclude that sex differences in survival may be due to differences in social status. I also suggest that worm/clam feeders and mussel-stabbers, feeding specialisations previously associated with lower survival rates, may have benefited more than mussel-hammerers from milder winter temperatures in recent years

Predicting the effect of local and global environmental change on shorebirds: a case study on the Exe estuary, U.K.

We used an individual-based model to assess site quality and to predict the effect of local (i.e. disturbance from a cycle path) and global (i.e. climate change) environmental change on the survival of six species of overwintering shorebirds on the Exe estuary, U.K. We also compare site quality on the Exe estuary with three other estuary Special Protection Areas (SPAs) and compare our predictions for the effects of climate change with predictions made for another southern U.K. estuary, Poole Harbour. Prey biomass densities in the Exe estuary were high for all six shorebirds, being as high as or higher than those found on other estuary SPAs. Simulations of increased levels of disturbance from a proposed cycle path along the side of the estuary predicted that disturbance of upper mudflat areas was unlikely to affect shorebird survival but that increased disturbance of nearby fields would reduce curlew survival. Shorebirds on the Exe estuary were far less seriously affected than those in Poole Harbour by reductions in mean daily temperatures, loss of terrestrial habitats and simulated sea-level rise. We conclude that the Exe estuary is a high quality estuary and that the shorebird populations modelled were less susceptible to climate change than those in Poole Harbour

Causes of variation in prey profitability and its consequences for the intake rate of the Oystercatcher Haematopus ostralegus

Prey species have different morphological and behavioural adaptations to escape their predators. In this paper we review how these prey defenses affect prey profitability and intake rate for one predator, the Oystercatcher. Four rules govern profitability. First, within each species large prey are more profitable than small prey, because flesh content increases more steeply with prey size than handling time. Second, soft-bodied prey, such as worms and leatherjackets, which can be swallowed whole, are much more profitable than armoured prey, such as bivalves, which Oystercatchers have to open before the flesh can be extracted from the shell. Third, heavily armoured surface-dwelling prey, like Mussels and Cockles, are the least profitable prey of all, even if the armour is bypassed through stabbing the bill between the valves. Fourth, within the burying prey species, the profitability of prey decreases with depth. Hence burying bivalve species that bury in winter at larger depth than in summer, are in winter, if not our of reach of the bill, anyway less profitable. Despite the large differences between the profitabilities of the various prey species, the intake rates do not differ much when the prey species are com pared, presumably because prey with a low profitability are only exploited if the search time is relatively short, i.e. if the density of harvestable prey is high. On the other hand, within each species, the intake rate goes up if larger, more profitable prey are taken. Thus, if the birds have to feed on smaller prey specimens, they fail to fully compensate for the low profitability by an increase in the rate at which these prey are found. Although the profitability of prey differs seasonally due to the variation in the prey condition, only a small seasonal variation in the intake rate was found. Because burying bivalves and soft-bodied worms bury deeper and are less active in winter, Oystercatchers necessarily rely on bivalves living at, or just beneath, the surface at that time of year

Predicting the effect of habitat change on waterfowl communities: a novel empirical approach

Natural environmental changes, such as coastal erosion, and human developments, ranging from roads and marinas to global climate change, are leading to much habitat change in wetlands. It would be valuable to conservationists, governments and developers tob be able to predict the likely act of such evolution on the internationally important waterbird populationsin European wetlands. We present a method, based on relatively easily and cheaply determined environmental variables, which allows the effect of habitat Change on estuary wateifowl cornmunities to be predicted. The factors that best describe waterfowl communities are estuary length, channel and shore widths, exposure to swell, sediment type, longitude and latitude. The implications for waterfowl of any habitat change that affects these variables are discussed. It is suggested that when human developments are being designed they should take these factors into account in an attempt to minimise their impact on waterfowl