Water, Sodium and Energy Turnover in Free-Living Little Penguins, Eudyptula-Minor

Abstract

Water influx rates of adult little penguins ranged from 20 ml kg-' day-' in fasting (incubating and moulting) birds to about 650 ml kg-' day- ' in birds that were foraging at sea over extended periods. The sodium influx rates of adults ranged from almost zero up to 87 mmol kg-' day-', depending on the activity patterns of the birds, and were closely correlated with water influxes. The metabolic rates of adult penguins were 1.7 and 2.8 times standard metabolic rates during fasting and foraging respectively, and were also closely correlated with water influx rates. The mean food consumption rate for the maintenance of chicks was about 236 g kg-' day-', equivalent to a maintenance energy intake of 1460 kJ kg-' day-'. Partitioning calculations show that sea water ingestion during foraging represented about 10% of total water influx, but about 40% of total sodium influx. Nasal salt secretions were hyperosmotic to serum and it was calculated that daily sodium influxes could be totally eliminated via this route within 4 hours.