JOHNSTON: CAYMAN ISLAND AVIFAUNA


 The climate of the Cayman Islands is characterized by mild to hot
 temperatures and a distinct dry season. A weather station maintained
 at Owen Roberts airfield on Grand Cayman provided the temperature
 and rainfall data in Table 1. From the data supplied by the weather
 station personnel, the mean annual high temperature was calculated to
 be 30C. Seasonal fluctuations in temperature are not extreme. On the
 other hand, both rainfall (annual mean of 154.9 cm) and prevailing
 winds do change seasonally. From May to October the prevailing winds
 are easterly, but through the winter months they tend to be from
 the northeast or northwest. A dry season extends from November
 through April, and periods of drought are frequent at other times. De-
 spite an annual wet season during the summer and autumn months, the
 islands' low relief, desiccating winds, shallow soils, and porosity of the
 limestone formation preclude the humid, tropical, luxuriant vegetation
 characteristic of many West Indian islands. In fact, much of the natural
 upland vegetation (see later discussion), including the introduced
 species, takes the form of low xerophytic scrub, many of the plants pos-
 sessing sharp spines and small leaves. Occasional autumnal hurricanes
 buffet the islands, and their effects may be quite severe, as was the hurri-
 cane of October 1944.


 TABLE 1.-TEMPERATURE AND RAINFALL MEASUREMENTS AT OWEN ROBERTS AIR-
 FIELD, GRAND CAYMAN, 1957-1970.

 Mean temperatures (C) Mean rainfall (cm)
 maximum minimum
 mean extreme mean extreme
 January 28 32 21 13 4.39
 February 28 31 21 11 3.30
 March 29 32 21 13 1.57
 April 30 32 21 15 4.52
 May 30 33 22 14 19.25
 June 31 34 24 21 23.93
 July 32 33 24 21 15.06
 August 32 33 23 22 15.82
 September 31 33 23 20 21.16
 October 30 32 23 21 27.25
 November 29 31 22 15 12.70
 December 28 30 22 14 7.11



 Through 1971, 151 species of birds had been recorded from the Cay-
S mans (Johnston et al. 1971). Most of these are North American migrants
 either in-transit or overwintering in the islands. A breakdown of the
 avifauna is as follows: