Diurnal activity budgets of breeding Eurasian Oystercatchers Haematopus ostralegus feeding on limpets on rocky shores

The effect of different stages of the tidal cycle, weather conditions and the presence of conand allo-specifics on the time and activity budgets of Eurasian Oystercatchers Haematopus ostralegus was investigated. Data were collected at a breeding site on Lundy Island in the Bristol Channel, UK, where Oystercatchers feed on limpets Patella spp. on rocky shores. Sixteen behaviours were recorded for 10-minute periods throughout the day. Grooming, feeding, antagonistic behaviours and alertness emerged as the four major behavioural categories from a Principal Component Analysis that was performed on the frequency and durational data. Oystercatchers were more active during low tide than high tide. Frequency and time spent on foraging were greatest during high falling and low falling tide. Time spent on grooming and frequency were high during high slack and falling tide. Alertness was at its maximum during high slack and low slack tide. No clear trend was found in relation to antagonistic behaviours. Type of habitat occupied was also found to have a significant effect on behavioural patterns. Amount of time allocated to different behaviours and the frequency of behaviours displayed a cyclical pattern based on the tide.