Justification of Red List Category
This species has an extremely 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 increasing, 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 is very large, and hence does not 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 global population is estimated to number c.120,000 individuals.
In North America, this species has undergone a small or statistically insignificant increase over the last 40 years (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).
Forster's Tern can be found in North and Central America, breeding seasonally in southern Canada and northern U.S.A., wintering in south-east and coastal south-western U.S.A., along the eastern and western coast of Mexico and in Central America. It can also be found year-round on the Atlantic coast of the U.S.A. from Virginia to Texas (del Hoyo et al. 1996).
This species breeds mainly at freshwater lakes, potholes, inland and coastal marshes and salt-pold dykes, and rarely on sand, mud or rocky islets. It feeds over lakes, streams and estuaries, favouring water less than 1 m deep. It feeds mainly on small fish (5-7 cm), but also aquatic insects and crustaceans. The exact composition of its diet and prey species varies depending on locality. It feeds mainly by plunge-diving or dipping from the surface, and occasionally diving from a perch in a kingfisher-like fashion. It has been seen to maintain a breeding territory. Breeding occurs between April and May on the Gulf Coast and to late May elsewhere, forming loose colonies of 5-250 pairs, though it is sometimes solitary. It prefers nesting among floating and emergent vegetation, but will also nest on boards, dredge spoil, sand or fine shell and on coarse gravel islands (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., Butchart, S., Calvert, R.
BirdLife International (2019) Species factsheet: Sterna forsteri. Downloaded from http://www.birdlife.org on 19/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/09/2019.