Sooty Terns Breeding on Palmyra

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Sooty Terns Breeding on Palmyra


This 1967 article was written for the Pacific Bird Observer, published in the late 1960s by the Smithsonian Institute as:

"...a newsletter distributed to collaborators of the Pacific Ocean Biological Survey Program of the Smithsonian Institution in order to promote a better understanding of birds and their relation to man in the Pacific."

Palmyra was a key location in the POBSP, and is mentioned in several of the Observer's issues, this article is the most descriptive of those, and includes several photographs. Be sure to check out the rest of the POBSP collection for more information!


Smithsonian Archives


Smithsonian Institute




Public Domain



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Palmyra (5°52'K, l62°06'W) is a coral atoll of many small islets on a barrier reef enclosing three distinct lagoons. The islets are scattered over an area 5 and 1/2 miles from east to west and l and 1/2 miles from north to south. They are low - the highest about six feet above sea level - and are heavily overgrown with vegetation. Coconut and other trees reach heights of 60 to 100 feet. Cooper Island, the largest islet, has an area of 46 acres and is on the northern side of the Atoll. During World War II an airbase with a runway 6000 feet long was constructed on Palmyra. Most of the base was located on Cooper Island.
After being abandoned in 1949, Palmyra was reoccupied for scientific purposes during 1960. The airstrip was an important part of the logistic support of the scientific program and was renovated. At present Palmyra is occupied by meteorologists working on the Line Islands Experiment, a project to study the meteorology of tropical disturbances, directed by the National Center for Atmospheric Research, Boulder, Colorado.
Sooty Terns are widespread and abundant tropical and subtropical birds, black above and white below, with a white forehead, black feet, legs, and bill. They are about 1 to 17 inches long. They feed on squid and small fish and are often seen skimming and hovering over the water. Their breeding varies throughout the year; in some areas it follows a regular annual cycle but in other areas the cycle may be irregular or even continuous. Sooty Terns breed in large colonies,which may contain as many as 500,000 birds or more . They do not build nests. Instead they usually lay their one egg on the bare ground. During February 17 to 20, 1967, while the USC&GS Ship SURVEYOR visited Palmyra, Sooty Terns were nesting on most of the abandoned airstrip. No other nesting areas were found. While renovating the runway for the Line Islands Experiment, it was unfortunately necessary to destroy a great number of freshly laid eggs. The construction work drove the adult birds into an area of approximately 16,000 square meters on the northeastern end of the airstrip. The density of terns in this area was about 6 birds per square meter, with only about 2 of these actually sitting Oil eggs . The Sooty Terns on eggs numbered more than 30,000 and the entire population was more than 95,000.

On March 27, 1967, when Pal- myra was visited again, over 95,000 eggs were observed in the airstrip colony. Some of the nests contained two eggs, which is not the normal clutch-size of the Sooty Tern. About 5 percent of the eggs had hatched. The oldest chicks were about 4 days old.

The importance in the role of the parent birds in the survival of the egg or chick was demonstrated during this visit. The parent birds shaded the egg or chick from the midday sun by standing over them until an approaching intruder ac- tually threatened them. Once the chicks were able to move about on their own other adults would chase them away from their nests as they did other intruders. I did not de- termine whether or not the parent birds recognized their own young.
Two new nesting sites were found during the March visit. They were on an abandoned causeway and were small colonies of only about 100 birds each. There was no major change in the population of the terns occupying the runway, even though it was frequently used by aircraft.

I believe that the breeding population of Sooty Terns on Palmyra has increased due to the construction and subsequent abandonment of the airbase. Construction of the airstrip cleared away heavy vegetation and the occasional renovation of the strip has maintained the clearing for the terns. Naturally clear areas on Palmyra include only a few small coral islets and Barren Island. These areas are subject to frequent flooding and probably could not support the present breeding population of Sooty Terns. This new man-improved Sooty Tern Breeding ground will be utilized as long as the airstrip is occasionally renovated. Should the airstrip become heavily overgrown, this Equatorial Pacific breeding ground probably would be lost.

The Sooty Terns on Palmyra demonstrate one of the ways wildlife can adapt to man’s activities.

Contributed by Christopher C. Mathewson Lieutenant Junior Grade E.S.S.A., Coast and Geodesic Survey


“Sooty Terns Breeding on Palmyra,” Palmyra Archive, accessed September 25, 2020,


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