The importance of plankton to Cassin's auklets during breeding

The breeding chronology, food habits, growth and reproductivesuccess of Cassin's Auklets, Ptychoramphus aleuticus, were investigatedon Triangle Island, British Columbia. The breeding of Cassin'sAuklets coincides with the plankton bloom in the eastern NorthPacific. Cassin's Auklets in British Columbia feed their youngmostly large copepods, Calanus cristatus, and euphausiids, chieflyThysanoessa spinifera, but fish was an important food item inone summer. Chicks which hatched early, grew and survived betterthan late-hatched chicks and this may relate to food availability.Adults and chicks on Triangle Island were heavier than thoseon South Farallon Island, California. The heavier weight andgreater numbers of Cassin's Auklets in British Columbia as comparedwith regions to the south may relate to Calanus cristatus availabilityand abundance in northern areas.