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
Christmas shearwater subalaris"). The Christmas shearwater is a slender-bodied shearwater, about 36 cm long, with a wingspan of around 75 cm, and weighs around 350 g. It has dark plumage all over, generally blackish-grey with a rusty-brown tinge, slightly paler on the underside of the bird, and with some small edging of white under the chin and pale fringes to the upperwing coverts. It has brown-grey feet and a dark bill and eyes. Both sexes are alike, as are the young after fledging. Nestlings are covered in dark grey down feathers. The species closely resembles the sooty ("Puffinus griseus") and short-tailed shearwaters