Sun compass in animals internal clock to determine their heading, and that they had learnt the actual direction down to the sea on their particular beach. Lockley's experiments with Manx shearwaters ("Puffinus puffinus") showed that when released "under a clear sky" far from their nests (in Skokholm), the seabirds first oriented themselves and then "flew off in a direct line for Skokholm", making the journey rapidly. For example, one of the birds, released at Boston airport, arrived in Skokholm 12½ days later; Lockley calculated that if the birds flew for 12 hours per day, they must have travelled at 20 miles per hour, their
Ilhéus do Rombo Cima is famous for its seabird colonies. Ilhéu Grande, which has been used by goat farmers and whalers in the past, does not currently support breeding seabirds, though large colonies must have existed formerly as the island has thick layers of guano. The island group has been identified as an Important Bird Area (IBA) by BirdLife International because it supports seabird colonies as well as peregrine falcons and Iago sparrows. Birds include the Frigate bird ("Pelagodroma marina") numbering around 1,000 in 1989, the Boyd's shearwater ("Puffinus boydi"), "Oceanodroma castro", Bulwer's petrel ("Bulweria bulwerii"), the brown booby ("Sula leucogaster") (50 pairs