干旱区生态环境知识资源中心

We present the first study of reproductive ecology of a mixed-species colony of Royal Tern (Thalasseus maximus) and Cayenne Tern (T. sandvicensis eurygnathus) on Isla Verde (Uruguay) during the 2005 breeding season. We also recorded breeding parameters of sympatric kelp gulls (Larus dominicanus) and predation rates on both tern species. The terns laying began during the second week of August and the breeding season ended between 10-19 November. Minimum population sizes were estimated on 350 and 27 breeding pairs of Royal and Cayenne Tern, respectively. They laid their eggs on the grass with a nest density of 8.6 nests/m(2) +/- 1.4 and mean clutch size was 1.03 and 1.00 for Royal and Cayenne Tern, respectively. The laying period of the Kelp Gull began between 28 August and 6 September, reaching the maximum number of breeding pairs (1095, CV = 57.3%) between 26 September and 2 October. Gulls nested all over the island (i.e., grass, sand-shell, and rocks); however the highest nest density was recorded on the grass. We observed a high spatial and temporal variability in terns breeding pairs. From aerial pictures we could detect that terns were deserting the nest from one side of the colony, while new clutches were recorded on the opposite side throughout the breeding season. Areas that had been abandoned by terns were then occupied by kelp gulls. This species was observed preying mostly on tern eggs at a rate of 0.03 predations/hour/nest. The terns breeding success was null at the end of the breeding season. As many factors could affect the tems breeding, predation by the Kelp Gull could have been the major cause that explains the dynamic observed. Accepted 4 July 2010.