Segregation in Timing of Breeding Reduces Inter-specific Competition in Tern Species on the Persian Gulf Islands

Several factors such as prey availability, weather, the age and experience of adults, day-length and probably othershave an effect on the timing of breeding in birds. We studied the timing of breeding in the Bridled Tern Sterna anaethetus, Lesser Crested Tern Sterna bengalensis and Greater Crested Tern Sterna bergii as the three most abundantsympatric seabird species on islands in the Persian Gulf. The results showed overlap in the timing of breeding among the three species. However, synchrony was found in individual mixed colonies of Lesser Crested Tern (11.3±0.16 days, range 8-17 days, n=10) and Greater Crested Tern (9.6±0.23 days, range 8-12 days, n=5), while there was a spread of over seven weeks in egglaying in the Bridled Tern. Commencement of nesting during the years of the study correlated closely with the arrival of spring weather and those factors which affected the oceanographic status of the Persian Gulf. High tides and weather conditions mostly affected low-lying nesting areas on the Khan Islands and in the coastal zone of Omol-Karam Island. We conclude that the timing of breeding cannot reduce intra-specific interactions in an assemblage of breeding seabirds in the Persian Gulf. However; asynchrony of breeding between mixed colonies of Lesser Crested Terns and Greater Crested Terns and in the whole colony of Bridled Terns could reduce inter-specific competition.