Measurement of chick provisioning in Antarctic prions Pachyptila desolata using an automated weighing system

The frequency and mass of meals delivered to ten Antarctic Prion Pachyptila desolata chicks nesting at Bird Island, South Georgia were examined using automated weighing systems, placed in the nest chamber of the burrow. The weighing systems, which consisted of an artificial nest platform mounted on electronic load cells linked to a data logger, recorded the mass of the chick every 10 min. Meal delivery was concentrated in the first few hours after dark with a peak (45% of meals) in the second hour of darkness. The mean number of meals per night per chick ranged from 0.4 to 1.7 with 80% of chicks receiving at least one meal per night; there were no nights when none of the chicks was fed. Chick 9, which had the highest feeding frequency, received smaller meals (mean 18 g) than all of the other chicks (mean 37 g). The mass of first and second meals delivered in the same night was not different nor was there a relationship between meal mass and feeding frequency (except for chick 9). There was no relationship between meal mass and chick age between 5 and 50 days. Meals delivered following a night when a chick received no meal were larger than when a chick had been fed the previous night. The proportion of chicks receiving 0, 1 and 2 meals per night differed from the predicted binomial distribution, assuming the independence of feeding by both parents, with more chicks receiving one meal per night than expected. Comparison with periodic weighing methods indicates that the latter underestimates meal size and feeding frequency. The variation within the small sample of chicks studied indicates the need for large sample sizes to estimate population provisioning parameters. However, the weighing system was very successful in providing accurate data on chick provisioning and, with additional development, could provide data on the individual provisioning strategies of adult birds.

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