We monitor the breeding population of Rhinoceros auklets on the Farallones by checking artificial wooden nest boxes distributed across the island. These boxes are visited on a regular basis to note which ones contain an active breeding pair, whether those pairs are successful at hatching an egg, and ultimately how many pairs end up fledging a chick; giving us an estimate of the annual breeding success for this species. In addition to the nest boxes, we also monitor breeding activity in Rabbit Cave, a large vestige of the islands geologic past that acts as a kind of massive burrow for Rhinoceros auklets. The entrance to Rabbit Cave starts out as a narrow crawl space that opens up into a cavernous amphitheatre at the back.