Download

Differences in the time of onset of breeding, morphology, egg size, plumage and vocalisations of Dark-rumped Petrels (Pterodroma phaeopygia phaeopygia) were investigated on four islands in the Galapagos. Comparisons were made with P. p. sandwichensis in Hawaii. In Galapagos, breeding cycles differed among islands, and on San Cristobal there were two populations that bred at different times. On Floreana, colonies at different altitudes bred at different times. Eggs were laid on Santiago over four consecutive months; on Santa Cruz the egg-laying period was shorter. Analyses of morphological measurements and notional volume separated Galapagos Dark-rumped Petrels into three groups. Birds on Santa Cruz and those breeding in the middle of the year on San Cristobal were the smallest; birds on Santiago and those breeding at the end of the year on San Cristobal were of intermediate size; and those on Floreana were the largest. There was a similar size trend in the breadth and volume of eggs. No relationship was found between variable plumage patterns on head and chest or between plumage and island populations. Evidence is presented that supports sexual dimorphism in vocalisations, and it is suggested that males make Sweet calls and females make Coarse calls. There were statistically significant interisland differences among Sweet calls and among Coarse calls. Dialects probably exist within the archipelago. Calls had either one or two introductory syllables. When present, the second introductory syllable was very similar to the single introductory syllable, and these may serve the same function. Discriminant analysis of Sweet calls correctly classified 82.296 of these into island of origin. A similar analysis of morphology correctly classified 58.6% of birds from five populations. A theoretical combination of these two analyses indicates a potential classification rate of 92.6%. Although there are differences among Galapagos populations, there is not yet sufficient evidence to warrant subspecific status. Vocalisations of the Hawaiian birds were quite different from those in Galapagos, and Galapagos birds were bigger. Dark-rumped Petrels in Galapagos and Hawaii might be more distant taxonomically than currently recognised and they may be different species.