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When feeding on blue mussels (Mytilus edulis), oystercatchers (Haematopus ostralegus) either stab into the mollusc's gaping valves or hammer through its dorsal or ventral shell. Whilst the selectivity of hammering and stabbing oystercatchers for specific prey morphologies has been well studied, the way in which the effects of environment on M. edulis morphology can in turn affect feeding methods of H. ostralegus is very poorly understood. Based on morphological analyses on randomly selected shells from three intertidal zones, this study failed to detect differences in morphology or distribution of dorsally and ventrally hammered shells but confirms the finding of previous authors that hammering oystercatchers select thinner mussels than stabbing birds. Additionally, we show that this difference in optimal prey morphology can lead to spatial patterns in oystercatcher feeding behaviour. Whilst at the low intertidal and higher mid intertidal zones, characterised by comparatively thick shells, most empty shells had apparently been stabbed, hammering was the dominant feeding behaviour at the lower mid intertidal zone, where shells were thinner. Preference of hammering birds for smaller mussels was not ubiquitous. Sagittal shell shape was predominantly influenced by allometric growth effects and had only minor effect on prey selection. All oystercatchers preferred less inlated mussels, with the degree of shell inflation gradually increasing with higher intertidal elevation. Our results illustrate the importance of small-scale patterns in prey ecophenotypes in determining the distribution and feeding dynamics of wading birds., Introduction Optimal foraging theory (OFT) states that, in order to maximise their net rate of energy intake, foraging predators must select prey that yields the maximum amount of energy for [...]

An experience of catching American oystercatchers at South Carolina's Cape Romain National Wildlife Refuge is described, which is a region-wide effort to learn more about these shy shorebirds and what they need to survive. The blood drawn from these birds can provide important clues about the overall health of America's ecosystem since any pesticide or heavy metal residue present in oysters will show up in oystercatchers.

Interference competition for food in oystercatchers, Haematopus ostralegus feeding on cockles, was examined. The probability of opening a cockle fell significantly as competitor density increased, and birds were more likely to carry cockles away. An optimal diet model showed that competitor density had only a negligible impact on overall intake rates. The dynamics of the process need to take into account the range of potentially complicated avoidance behaviours.

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 differential habitats of Pied and Sooty Oystercatchers at general habitat levels helps them to coexist ecologically in the Furneaux Islands in Australia. Coastal birds prefer to nest in higher densities on small islands to reduce predation risk and to lower human disturbance levels. The location of nesting depends on preferred feeding substrates and the choice of rock or sand. The Sooty variety nest only in small rocky islands while the Pied ones choose islands that are sandy. Behavioral observations show a lack of thermoregulatory stress between the two species.

Divorce in osytercatchers, though rare, occurs when there is a desire for a change in the male partner or when there is a competition for good males or good territories. The females show a tendency to divorce when they are provided with an option of moving to better territories. However, the reproductive success of divorced birds is lower when the change of male partners is made during the breeding season.

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.

The results of aerial survey, which examine the occurrence and wintering habitat of oystercatchers, are presented.

The fitness consequences of divorce in oystercatchers are investigated. In this investigation a distinction between two types of divorce is made.

Eurasian Oystercatchers (Haematopus ostralegus) breeding on the salt marsh of Schiermonnikoog (Dutch Wadden Sea) lose many eggs to predators, mainly Herring (Larus argentatus) and Mew gulls (L. canus). We estimated that the probability for an egg to survive from laying until hatching was 69%. Daily egg mortality was higher during the laying period than during the incubation period. When researchers were present in the study area, oystercatchers spent more time at greater distances from the nest. We investigated whether human disturbance resulted in more eggs being lost to predators. Two experimental areas were in turn visited at high and at low frequency. From a preliminary analysis, we estimated higher daily egg mortality rates when nests were checked three times per day instead of once every other day. However, high-frequency nest checks provided more information on newly laid and lost eggs, especially during the laying period. After correcting for that extra information (by simply deleting it), the egg mortality rates were no longer different. We conclude that human disturbance did not increase egg loss, rather egg mortality rates were underestimated when nests were checked only once per two days.