Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The combined populations of Anous ceruleus and A. albivitta are estimated to number 27,000-120,000 individuals, but the total for A. cerulea is unknown.
The overall population trend is stable, although some populations have unknown trends (Delany and Scott 2006).
This species takes very small fish (average length 17 mm), squid, crustaceans and pelagic sea striders with proportions varying seasonally and geographically. It feeds on the wing by dipping or pattering. Breeding can be continual in places (e.g. Hawaii) and occurs in loose colonies on cliffs or rocky areas (del Hoyo et al. 1996).
At present there are no factors thought to pose a genuine threat to this species.
Text account compilers
Ekstrom, J., Symes, A., Taylor, J., Butchart, S., Martin, R., Calvert, R.
BirdLife International (2022) Species factsheet: Anous ceruleus. Downloaded from http://www.birdlife.org on 07/10/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/10/2022.