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Features of Natural Interest

Interestingly, sooty terns were the only species of seabird that nested abundantly on the main island of Ascension while feral cats were still present. This is likely to be due to the large size and density of their breeding groups which can reach up to approximately 200,000 pairs, and their synchronous breeding which settled into a 9.6 month cycle when cats were present. This has started to change in the last couple of years following the feral cat eradication. There is usually a peak in the number of sooty terns breeding every 9.6 months: however birds can breed year round. This is likely due to the lack of predation pressure, allowing the birds to nest in smaller groups. 

Sooty terns flying over colony.

© Dr Mike Pienkowski
(Features of Natural Interest, 5 of 32 - Slide ref. 605)