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Research was conducted to study the trade-off between food finding and food stealing in the young oystercatchers, Haematopus ostralegus. Juvenile foraging behavior was compared with that of older birds to identify changes in juvenile decision taking from behavioral changes induced by the foraging environment. Additional data on time cost were also collected to evaluate the profitability of stealing a mussel rather than finding one on the mussel bed.

The habit of nocturnal foraging in wildfowl (Anseriformes) and shorebirds (Charadrii) and its significance were investigated. The emergence of this habit in various bird species were due to factors which differ according to species, region and circumstances. Various adaptations for nocturnal feeding were discussed. Nocturnal foraging was mainly attributed either to the advantages from dcreased chances of encountering predators at night, or to the need to supplement nutrition because of failure to satisfy food requirements during the day. The implications for time and energy budget studies based on daytime studies were discussed.

Field observations were made of the size selection of mussels by oystercatchers throughout the year. Birds that opened mussels by hammering through the shell selected thin-shelled individuals and fed disproportionately on intermediate size classes for most months of the year. Profitability increased monotonically with mussel length for dorsal hammerers, but peaked at an intermediate size for ventral hammerers. In spring, all oystercatchers switched to feeding on small mussels and this coincided with weight loss in large mussels associated with spawning. An optimal diet model, which in addition to handling time included both the probabilistic costs of making selection errors and encounter rates with thin-shelled mussels, was a good predictor of the birds' diet selection for most months of the year, but did not explain why hammerers ate such small mussels in spring. These results are discussed in relation to some of the assumptions implicit in the model.

Disturbance of wildlife is a potential cause of conservation concern, not least to overwintering waders Charadrii inhabiting estuaries close to conurbations where human recreational and economic activities are often concentrated. Disturbance from people on and alongside intertidal foraging areas could make it more difficult for birds to survive until spring in good condition by reducing the time available for foraging, increasing energy requirements and displacing birds to poorer foraging areas. We adopted a two‐part approach to testing whether such significant impacts occurred in a Special Protection Area where disturbance risk was high because of its small size and close proximity to conurbations. In part one, we recorded over the whole estuary during stages of the tidal cycle when part or all of the intertidal zone was exposed and so accessible to waders (i.e. on receding, low and advancing tides): (1) the numbers and activities of people on the intertidal flats and on the adjacent land in those places where people were visible to waders in the intertidal zone and (2) the numbers of waders present and disturbed into flight, the flight distance and flight duration in the 'overlap' areas where people did disturb waders. People occurred on < 25% of the 938 ha of intertidal flats, but most waders foraged on mudflats, whereas most people were on sandflats. People on land were visible to foraging waders along < 35% of the 16.5 km of shoreline. Waders and people were therefore substantially separated in space. Within overlap areas, people and waders were often frequently separated in time: for example, people on land mostly disturbed waders when only the upper shore levels were exposed. The average overwintering wader spent < 0.1% of its foraging time during daylight flying away from people and the additional energy expenditure was equivalent to < 0.02% of its daily requirements. The comparison made in part two between our study area and two comparable estuaries showed that the number of visits each day to the overlap areas would need to be 29 or 43 times greater for disturbance to have lowered the birds' body condition and winter survival. Both parts of the study therefore suggested strongly that the amount of disturbance was too trivial to have a significant impact on waders. It is concluded that: (1) to properly assess disturbance risk to waders, both extensive and intensive observations must be made on the behaviour of people and birds to quantify the extent to which they overlap in space and time, and (2) it should not be assumed that an estuary's close proximity to conurbations, and the presence of large numbers of people in the vicinity of the SPA, necessarily implies a significant disturbance risk to waders. [ABSTRACT FROM AUTHOR]

The functional responses of free-living shorebirds (Charadriiformes) eating macro-invertebrates in which intake rate is expressed as a function of numerical prey density, is described. The resulting equations have provided a convenient way of estimating intake rate for many kinds of studies for which the intake rate is a critical piece of information.