IN the past, almost without exception, zoologists have reported constant activity among birds and other animals in the perpetual light of the arctic summer. This is possibly accounted for by the extreme vigilance of all tundra species, coupled with the open nature of the country which renders the human observer visible at great distances. These arctic animals, naturally, are exceptionally alert, because of the open nature of their habitat. They have usually vacated their nesting or resting places and are very active indeed long before they are seen by the observer. During a recent summer expedition to West Spitsbergen (Svalbard) attention was paid to the question of perpetual activity. Certain species of birds, notably the tern (Sterna macrura), the eider duck (Somateria mollissima), the skua (Stercorarius parasiticus) and possibly the purple sandpiper (Calidris maritima) undergo a distinct period of quiescence. At Klaas Billen Bay, in the Inner Fjord Zone (Summerhayes, V. S. & Elton, C. S. (1928), J. Ecol. 16: 256) this period appeared to extend for a couple of hours after 1 a.m. each day. It coincides roughly with the time during which the sunlight, temperature, and wind velocity are at a minimum. (For this information I am indebted to Prof. H. Tollner of the Zentralanstalt fur Meteorologie, Vienna, a co-worker on our expedition.) On one species only could satisfactory observation be made. This was the arctic tern, which had established an extensive ternery on the shingle about the huts in which we lived. These birds were in residence before we arrived, and after the first few hours we were subjected to a vicious attack by them every time we left the huts. They unmercifully persecuted the fulmar petrels and gulls which flew over the ternery from time to time, and no robbing skua dared approach their colony. During the quiescent period however, when the sitting tern slept on the eggs and its mate fitfully dozed a few yards away, passing kittiwakes (Rissa tridactyla) and fulmars (Fulmarus glacialis) and even the hereditary enemy the skua were allowed to fly over low without molestation. Despite the fact that the sitting bird was sleeping, the non-sitting bird never slept for more than a few minutes at a time. Time and again it would suddenly untuck its head and gaze suspiciously around, often making a short flight as if to satisfy itself that all was well. A human figure appearing half a mile away over the barren tundra would provoke the whole colony into noisy