.--Extreme extralimital
vagrancy is common in seabirds, particularly among the petrels of the order Pro-
cellariiformes (Bourne 1967). It is also known in tropical terns, Sterninae, but is
less well-documented (e.g. Peterson and Watson 1971). We report here a record
of a White Tern (Gygis alba) on Bermuda. So far as we can determine this is
the first recorded occurrence of the species north of the Equator in the Atlantic
Ocean. What is particularly remarkable about this record is that the individual
appears to be a vagrant from the Pacific Ocean rather than from the tropical
South Atlantic Ocean where it also breeds.
The bird was observed and photographed at less than 3 m in the Great Sound,
Bermuda from 7-9 December 1972 by Wingate (Figure 1). It was feeding on
fry (small baitfish of the herring family) in company with a flock of Common
Terns (Sterna hitundo) and, compared with that species, seemed similar or only
slightly smaller in size. Unlike the Common Terns, which were "surface plunging"
to catch fry, this bird was swooping and catching the fish in midair as they
jumped--the "air-dipping" method of feeding typical of the White Tern (Ashmole
and Ashmole 1967). During most of the time that it was observed, it remained
flying and very active, moving rapidly from one school of jumping fry to another.
Only rarely did it settle on buoys and reef markers where it was invariably dis-
placed by the more aggressive Common Terns.
The White Tern appeared to be in good condition with immaculate plumage,
although obviously undergoing wing and tail molt (Figure 1). There were no
signs of feather wear or fouling to suggest that it might have been transported in
captivity.
Figure 1. Vfhite Tern in Great Sound, Bermuda 7 December 1972. Note feather-
ing and extensive blue area at base of bill, dark rhachis on outer primary and xving
molt.
Figure 2. Heads (from top to bottom) of Gygis alba rnicrorhyncha from
Marquesas Islands, G. a. alba from Ascension Island and G. a. candida from
Clipperton Island.
Two groups of subspecies of White Terns are occasionally treated as distinct
species. One, which is represented by a number of named subspecies in the Pacific
and Indian Oceans, can be conveniently called the candida group. It has a deeply
forked tail, dark rhaches on the primaries, a relatively deep bill with a pronounced
blue area near the base, and a straight diagonal margin between the facial feathering
and the maxillary rhamphotheca (Figure 2). The other group consists of two
subspecies, nominate alba in the Atlantic (breeds on Fernando Noronha, Martin
Vas, Trindade, Ascension, and St. Helena) and microrhyncha in the Marquesas and
possibly some of the Line and Phoenix Islands in the east central Pacific Ocean.
These alba-microrhyncha birds have a less deeply forked tail, far less dark pig-
mentation on the primary rhaches, a slender bill with little blue at the base,
and loral feathering that extends in an acute angle forward on the bill toward
the nostril (Figure 2). Pacific Ocean microrhyncha is markedly smaller and has
a less deeply forked tail, and a much more slender bill than Atlantic Ocean alba.
Surprisingly, the tern photographed on Bermuda (Figure 1) shows clearly the
bill characters and dark primary rhachis pigmentation of the candida group rather
than those of the Atlantic alba population as one would have expected. It is
impossible to ascertain from the photograph, however, whether it belongs to north
Pacific pacifica, south central Pacific candida, or Indian Ocean monte, which
only differ slightly in average measurements (Baker 1951: 174-181). We suppose
that if the Bermuda individual was in fact a vagrant, it more probably was
candida, from one of the nearer eastern Pacific islands (Clipperton, Cocos, or
Revilla Gigedo), that crossed the Isthmus of Panama, rather than C. a. monte
that made the longer journey from the Indian Ocean around the Cape of Good
Hope.
We have sought in vain a simple meteorological explanation for this record.
R. L. Pyle of the National Oceanic and Atmospheric Administration has examined
for us National Weather Service daily analyses of the Topical Oceanic Lower Level
(up to 800 m) from 1 October through mid-November 1972. They show a per-
sistent wind flow from the east and northeast throughout the Caribbean-Antillean
region. Likewise in the eastern Pacific the normal col area of light variable winds
was present south and west of the isthmus most of the period, with light easterly
and northeasterly winds north to 25 ø N and beyond. The same general wind pat-
terns existed up to at least 1,600 m and probably well beyond that height.
Although these wind patterns would not have hindered a White Tern from traveling
east from the Pacific Ocean, there were no anomalously favorable winds to have
assisted it. Nor were there any abnormal weather patterns at Bermuda during
the 2 months prior to this sighting.
Ashmole and Ashmole (1967: 66, 97) have suggested that the White Tern is
adapted for feeding at low light intensities far at sea and, like the Sooty Tern
(Sterna fuscata), may sleep on the wing (Ashmole 1963). Wingate observed be-
havior in an immature Sooty Tern over Castle Harbor Bermuda, that strongly
suggested it had been sleeping on the wing. The bird was drifting downwind in
wide circles at 20 m altitude in the wake of a passing hurricane. It narrowly
missed a high rock and nearly flew into a hillside of the main island before
suddenly breaking its aimless drifting and flying back out of the harbor. Inland
vagrant records of petrels, tropicbirds, frigatebirds, and terns suggest that seabirds
may occasionally soar to great heights and get blown far inland over the con-
tinents, especially in overcast or stormy conditions (e.g.A.O.U. 1957: 18, 19, 27,
40, 237, 328).
We lean toward the view that the White Tern recorded on Bermuda was a
vagrant candida that crossed the isthmus passively, possibly while asleep on the
wing, but cannot account for its occurrence at the latitude of Bermuda in De
cember. It seems far more likely that an individual of this species entering the
Caribbean would have remained in the vicinity of the Antilles, but Bond (in
litt.) knows of no records from that area.
In view of this, the possibility that the bird was tramported by ship either
having come aboard to rest or as a temporary captive cannot be completely
excluded. Inasmuch as Bermuda is visited by ships that enter the Atlantic Ocean
both from the Pacific Ocean through the Panama Canal and from the Indian
Ocean around the Cape of Good Hope, if a captive it could just as likely have been
G. a. monte from the Indian Ocean.
We are grateful to R. A. Slaughter who took the color slide from which
Figure 1 is reproduced, to S. L. Olson who pointed out to us unresolved systematic
problems in the Pacific Ocean populations, and R. L. Pyle for looking up and
interpreting meteorological information for us.
ANiERICAN ORi'ITIIOI, OGISTS' UNION. 1957. Check~list of North American birds,
fifth ed. Baltimore, Amer. Ornithol. Union.
As>ro, N. P. 1963. The biology of the wideawake or Sooty Tern Sterna
fuscata on Ascension Island. Ibis 103b: 297-364.
As{o, N. P., A>m M. J. As>ro. 1967. Comparative feeding ecology of sea-
birds of a tropical oceanic island. Peabody Mus. Nat. Hist. Bull. 24:1-131.
BAKER, R. H. 1951. The avifauna of Micronesia, its origin, evolution, and dis-
tribution. Univ. Kansas Mus. Nat. Hist. Publ. 3: 1-359.
BOUR>E, W. R. P. 1967. Long-distance vagrancy in the petrels. Ibis 109: 141-
167.
PTESO>, R. T., A>m G. E. WArSO>. 1971. Franklin's Gull and Bridled Tern
in southern Chile. Auk 88: 670-671.
DAVID B. WI>CAZE, Department of Agriculture and Fisherles, P.O. Box 834,
Hamilton, Bermuda, and Goc E. WATSO>, National Museum of Natural History,
Smithsonian Institution, Washington, D.C. 20560. Accepted 10 Jun. 73.