TIME ALLOCATION AND FORAGING PATTERN OF CHICK-REARING RAZORBILLS IN NORTHWEST ICELAND

A newly modified, bird-borne data-logger was used to investigate the flight activity and diving behavior of foraging Razorbills (Alca torda) breeding at Latrabjarg, northwest Iceland. The recorders allowed us to determine with high time-resolution all relevant movements in 47 complete foraging trips of 29 different Razorbills during two successive breeding seasons, 1997 and 1998. In 1998, direction recorders equipped with a compass recorded 19 foraging routes of 10 different Razorbills. The trips consisted of a number of flights interrupted by short series of diving bouts by which the birds seemingly explored areas for prey availability. Foraging occurred at sites where Razorbills stopped, dived, and rested for a long time before returning to the nest by a single flight or a sequence of a few flights. The majority of dive profiles (n = 17 095 dives) consisted of nonstop downward and upward movements to depths rarely greater than 35 m, and never exceeding 41 m. There was considerable diurnal variation in foraging behavior, expressed by more frequent and shallower dives around midnight. The Razorbill's diving pattern turns out to be very different from that reported for Thick-billed Murres (Uria lomvia) breeding in the same colony. Considerable differences in duration of trips, average number of dives, and time allocation were observed between the two breeding seasons, suggesting differences in foraging conditions for the birds. Asignación de Tiempo y Patrones de Forrajeo durante la Crianza de los Pichones en Alca torda en el Noroeste de Islandia Resumen. Un archivador de datos recientemente modificado que se acopla a las aves fue utilizado para investigar la actividad de vuelo y el comportamiento de buceo de individuos reproductivos de Alca torda en Latrabjarg, noroeste de Islandia. Los equipos nos permitieron determinar con una alta resolución de tiempo todos los movimientos relevantes en 47 viajes de forrajeo de 29 individuos diferentes durante dos temporadas reproductivas sucesivas (1997 y 1998). En 1998, equipos registradores de dirección equipados con una brújula, registraron 19 rutas de forrajeo de 10 individuos diferentes. Los viajes consistieron en un número de vuelos interrumpidos por pequeñas series de sesiones de buceo por medio de las cuales las aves aparentemente investigaban la disponibilidad de presas en distintas áreas. El forrajeo tuvo lugar en sitios donde las aves se detuvieron, bucearon y descansaron por un período prolongado antes de re