Observations on the Birds of St. John, Virgin Islands

Abstract

Location and physiography. St. John (Figure 1) lies about 88 km (55 miles) east of Puerto Rico, centrally situated among the American and British Virgin Islands. It is separated from St. Thomas to the west and from several islands of the British group to the north and east by channels one and one-half to five km wide. St. Croix is directly south about 64 km (40 miles). St. John has an area of about 48 km2 (19 square miles), of which roughly three quarters is within the tentative boundaries of Virgin Islands National Park. The topography features deep valleys and slopes that rise abruptly from the shore (Figure 2). Meyerhoff (1926) stated that the present Virgin Islands are the summits of a complex mountain range made up of stratified volcanic accumulations with much intrusive material. With the central mountains of Puerto Rico, they form one of the oldest continuously emerged land areas in the West Indies, having apparently stood above water since the late Cretaceous (Schuchert, 1935: 477). Relationships of geological structure and history are entirely with the Greater Antilles. Ocean depths between the northern Virgin Islands and Puerto Rico scarcely exceed 55 meters (30 fathoms), and a continuous land area probably existed at many times in the past and as recently as late in the Pleistocene (Schuchert, 1935: ff. p. 767). St. Croix is geologically similar but now isolated from the northern islands by depths of more than 3,700 meters (2,000 fathoms). Meyerhoff (1926) considered that the separation resulted from block-faulting during the Pliocene. Climate. Temperatures are constant and high. Data for Cruz Bay, St. John, for 1939 show a mean annual temperature of 23.90 C (79.9? F), a mean daily range of 6.40 C (11.50 F), and an extreme range of 18-34? C (65-93? F) (Stone, 1942). Rainfall tends to be local and highly variable. Mean annual rainfall at six St. John stations for various parts of the span 1877-1940 was about 100-150 cm (40 to 60 inches), with extremes of about 64 and 240 cm (25 and 95 inches) and frequent wide variation between nearby stations in a given year (Stone, U.c.). Areas above 300-meter