NO. 2298. THE GUANO BIRDS OF PERU—COKER. 463 



and apparently quite unobservant of the boat. Not more than once 

 did I see them on the water by day, though the fishermen said that 

 but one bu-d of the pair is at the nest during the day, the other remain- 

 ing out on the ocean. On the islands, as far as my observations go, 

 they are strictly nocturnal, coming and going only after daylight has 

 gone and before the Ught of morning. They are more readily recog- 

 nizable by sound than sight, and, as they fly obscurely about over 

 the island, uttering their little croaks, they are very suggestive of 

 bats. 



The nests are made in the side of the hill, often just beneath a 

 large rock or sheltered imder the hard salty crust. It is an odd 

 experience to sit at such a place and hear the mysterious sounds 

 from subterranean homes. Over and over again, with the voice of 

 a frog, unvaried in pitch or rhythm, they repeat the sequence of 

 notes — two longs, a short and a long, the last note shghtly longer 

 than the first two. Another more complicated sound is made by 

 some and it is possible that the calls are distinctive of the sexes. 



The potoyunco is comparatively small, measuring about 10 inches 

 in full length from end of biU to tip of tail and weighing half a pound. 

 The general color is black above and white below. The body is 

 thickly covered with feathers, beneath which is a thick gray down, 

 the dense coat making the bird appear to possess a very large body. 

 Viewed from below, the body is oval in form — like a large white 

 egg — the wings and the short,, stout neck seeming disproportionately 

 small appendages. 



A number of the nests were observed at the Ballestas North Island, 

 and the birds were heard on the Chinchas, but the lofty San Gallan 

 was the chief island for potoyuncos, as the potoyuncos were easily 

 the principal bird of this large island. 



San Gallan, 2.5 by 1.5 miles, is mostly dry, barren, and dusty, 

 but with high hills reaching well into the clouds, and only there, in 

 the moist altitudes, teemmg with plant life. Everywhere over the 

 island are large spots perforated by the holes of the potoyuncos, as 

 they undermine the hard, dry crust of the lower hillsides or burrow 

 back underneath the vegetation of the cloud-wrapped peaks more 

 than a thousand feet above sea level. 



Searching for these birds m the daytime one is guided only by the 

 openings of the burrows, for then- voice is rarely heard during the 

 day. One may try quite a number of nests without result, as the 

 burrow may either be unoccupied or, more often, too deep for the 

 arm to reach to the nest. Still, so abimdant are the nests on San 

 Gallan, that a considerable number of birds or eggs may be cap- 

 tured in an hour or two. Once reached, the birds are easily taken, 

 as they make almost no effort at resistance. Sometimes, after they 

 are out, they try to bite, but without inflicting injury. Occasionally 

 they would rush into the hands held at the mouth of the burrow. 



