Inca Tern Larosterna inca


Justification of Red List Category
This species is listed as Near Threatened because its population has apparently experienced a moderately rapid decline.

Population justification
The total population has been estimated more than 150,000 individuals (Zavaga et al. unpublished data).

Trend justification
Survey data suggest that moderately rapid declines have occurred.

Distribution and population

Larosterna inca is found along the Pacific coast from northern Peru south to central Chile. Mass dispersal and breeding failures have resulted periodically from El Niño Southern Oscillation (ENSO) events, and both fish-stocks and the populations of seabirds that depend upon them are adapted to these fluctuations. Population declines are usually promptly reversed, suggesting that food shortages trigger rapid dispersal not high mortality in adults and high reproduction rates (up to two successful broods in a year). Although fishing for anchoveta has been banned in Peru, and the guano industry adequately regulated, there are concerns that this species might be badly affected by the El Niño Southern Oscillation event of 1998 (G. Engblom in litt. 2003). Prior to the guano industry (c.1850) there were millions of Inca Terns in Peru (according to accounts from Coker 1919, Hutchison 1950). Current numbers are much lower than two centuries ago, but they are common and breed in some localities. The total population has been estimated at more than 150,000 individuals (Zavalaga et al. unpublished data).


It breeds on inshore (and occasionally offshore) islands and rocky coastal cliffs. Nests are placed in suitable fissures, burrows, caves and cavities, sometimes the old nest of a Humboldt Penguin Spheniscus humboldti. It feeds, often in large flocks, on schooling anchoveta Engraulis ringens, mote sculpins Normanychtic crokeri and silversides Odothestes regia regia found in the cold water of the Humboldt Current. Additionally, this species scavenges offal and scraps from sea-lions and fishing boats. One or two eggs are incubated for about four weeks, and the chicks leave the nest after seven weeks. Birds feed by plunge diving for fish.


Reproductive success is dramatically reduced during El Niño events: for example, all birds abandoned breeding attempts during the first part of 2014 at Punta San Juan (Merino 2017), but the population is capable of rebounding with sufficient time between events and in the absence of other threats. Mass reproductive failure can also be caused by rat predation, as recorded in Punta San Juan (Merino 2017). Cats are also present across much of the Inca Tern’s range and have been found to affect other birds, such as the Peruvian Diving-petrel Pelecanoides garnotii, but there is no evidence of a direct impact on the Inca Tern.

The Inca Tern has been recorded attending a commercial trawler (Weichler et al. 2004) and as bycatch in the artisanal Peruvian drift-net fishery, indicating a level of mortality occurring in this poorly monitored fishery, but only a single individual was killed in 914 sets (Mangel 2012), suggesting that the level of this bycatch is relatively low. Heavy harvesting of Peruvian anchovy, and the subsequent reduction of anchovy stocks, is considered to have been sufficient to impact breeding success, though there appears little direct evidence of the relative influence of harvest levels versus El Niño impacts. Guano harvesting may have an effect on population dynamics. However, Inca Terns are very flexible and successful in using any kind of coverage, natural or artificial, for nesting and, as such, guano mining seems to have a negligible effect on the overall population.

Conservation actions

Conservation Actions Underway
Some breeding sites lie within managed guano reserves or protected areas.

Conservation Actions Proposed
Identify those breeding sites where introduced predators are a problem and control/remove them from these sites. Determine effects of interactions with fisheries. Monitor population levels at key sites. Establish key locations as Marine Protected Areas.


41cm. It can be identified by its dark grey body, white moustache on both sides of its head, and red-orange beak and feet. Juveniles lack moustache and have brown plumage and bare parts. Similar species: Adults unmistakeable, juveniles could be mistaken for noddy sps.


Text account compilers
Benstead, P., Lascelles, B., Martin, R., Frere, E., Palmer-Newton, A., Butchart, S., Sharpe, C.J., Stuart, A.

Engblom, G., Zavalaga, C.

Recommended citation
BirdLife International (2022) Species factsheet: Larosterna inca. Downloaded from http://www.birdlife.org on 27/09/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 27/09/2022.