FAMILY PROCELLARIIDAE 39 



a longer island, separated in several sections, which is known to 

 local fishermen as Tiger Rock. At the western end the higher part 

 is nearly divided by a cleft through which storm waves may wash. 

 The shearwater colony is located in burrows at the summit of the 

 eastern sector of this islet, on the steep, landward slope beneath a 

 scattered grove of guarumos and coconut palms, with undergrowth 

 of cafia blanca, coarse-leaved grasses, and other herbaceous plants. 



The birds were noted here first by Loye Holmes Miller in 1936, 

 during a brief visit to the Chiriqui Lagoon area, where he had 

 quarters on a survey ship of the Hydrographic Office of the Navy. 

 According to notes that Dr. Miller has supplied he was told by a 

 seaman of birds nesting in holes on a rocky island. He visited the 

 site on March 12 and found 4 occupied burrows of Audubon's 

 shearwater with eggs. He collected two skins, a skeleton, and some 

 miscellaneous bones from bodies left by vultures. The specimens, 

 in the collections of the University of California at Los Angeles, 

 attracted no special attention, for it was not realized that they marked 

 a considerable extension of range. 



During my work in the Almirante region in 1958 Thomas W. Dunn, 

 through his detailed knowledge gained in fishing these waters, 

 identified the locality shown on the sketch map Miller had furnished. 

 And on February 28, with favorable weather, I crossed from Al- 

 mirante to the Tiger Cays in a small cayuco driven by an outboard 

 motor. Though a heavy swell prevented our beaching the boat, I 

 landed without difficulty at the cleft on the leeward side of Tiger 

 Rock and within a few minutes had located the shearwaters on the 

 upper slopes of the island. The colony, or the part of it that I 

 examined, covered an area about 10 by 20 meters on the leeward 

 side of the eastern knob near its summit. The occupied section lay 

 midway on the steep slope between the high ridge and the point where 

 there was a nearly vertical descent to the sea. Here there was an 

 accumulation of humus and fine clay, dotted with openings leading 

 into the numerous burrows excavated by the birds. Since the soil was 

 penetrated by tangles of roots of the broad-leaved plants that shaded 

 the surface, the birds had difficulty in digging, as the average length 

 of the burrows was less than three-quarters of a meter. Part, located 

 in pockets where rainwater accumulated, were wet, so that breasts and 

 ends of wings and tails of birds that inhabited them were heavily 

 stained with mud. In nests with proper drainage birds and their eggs 

 were clean. The series of 9 shearwaters collected included 4 males and 

 5 females, each found with a single egg, except one, and there may 



