Breeding Success

At TRS, breeding success was estimated for seven species. This parameter is very important to assess the productivity of the bird colonies in terms of chicks fledged and to identify threats or stressors that lead to lower breeding success. For example, if predators are present on one island, there will likely be fewer chicks fledging. Tracking this parameter will help us identify key areas for intervention and give us early indications of future population trends.

In general, the breeding success was quite variable among species. We only tracked two osprey nests, but all seven of their eggs laid resulted in fledged chicks. In contrast, only 10 of 50 (20%) Brown booby eggs resulted in fledged chicks. The cause of low survivorship of smaller chicks of this species will be a focal area for us in coming years. Great and Lesser crested terns showed quite high breeding success (82% and 74%, respectively), but White-cheeked terns struggled to breed successfully (32%). This year, for reasons that are unclear, many White-cheeked tern nests were established in unsuitable places such as mangrove areas. Many birds nesting in mangroves lost their eggs during high-tide events. In contrast, Sooty falcons had a quite high breeding success (63%), although this was marginally lower than in 2021 (68%). However, as the average number of eggs per breeding pair was considerably higher in 2022 than 2021, the number of chicks fledged per pair was greater in 2022. There were 81 fledged chicks this year.