TROPICBIRD IDENTIFICATION by Don Roberson

These tropicbirds are, respectively, two Red-tailed Tropicbirds (upper two photos; lefthand bird is quite young and tailless but is out of juvenal plumage), an adult White-tailed Tropicbird (center) and an adult Red-billed Tropicbird (bottom). No matter what age the tropicbird may be, the important i.d. points are these:

• Forget the tail for i.d. purposes! Young Red-tailed Tropicbirds have white tails (see upper right hand bird). Every Red-tailed that I've seen at sea (dozens in the eastern tropical Pacific) had a white or (at most) a pale pinkish tail. Only adults on the breeding grounds have obvious red tails. Further, tail color can be hard to determine against a bright blue sky. So forget about the tails (the other two species have white tails but even these can look pinkish when backlit, and some populations of White-tailed actually have a pinkish or yellowish cast to the tail at times).
• Forget the bill color for i.d. purposes! Both Red-billed and Red-tailed have red bills as adults, and even typically yellow-billed adult White-tailed can appear orange to orange-red in some lights and angles. Young birds of any species can have dingy or darkish bills. Young Red-tails go through a sequence from dark to two-tone bills, to quite yellowish and then orange, before they become red.
• Upperwing patterns are diagnostic. At all ages, Red-tailed Tropicbird has virtually all-white remiges (primaries and secondaries) so they look essentially "white-winged" in the field. This works both on quite young birds (upper left) and older individuals (upper right) up through adults. This is easy! [In the photos later on of young birds you will see that the outer primaries on some Red-tails have black shaft streaks, and some tertials have black centers, but these are very fine points. All Red-tails appear essentially white-winged in the field.]
• Only White-tailed Tropicbird has a black "carpal bar" [=ulnar bar] forming black braces on the sides of the body, and it has the base of the outer four primaries black. The extent of black in the primaries varies geographically (and has accounted for the naming of several races; Orta 1992). A key point, though, is that the black outer primaries contrast with the white primary coverts.
• Only Red-billed Tropicbird has both black outer primaries and black primary coverts. Note how different this pattern is from White-tailed. Yes, Red-billed also has much barring on the back, but so do juvenal plumages of all species, so I would de-emphasize that character.
• Only Red-billed Tropicbird has a black nuchal collar that connects the black face patches around the nape. All tropicbirds have black patches around their eyes, but only the Red-billed connects around the collar.

• all white remiges -- the lower left bird -- is a Red-tailed
• dark outer primaries contrast with white underwing coverts -- upper bird -- is White-tailed
• both outer primaries and underwing primary coverts dark -- middle bird -- is Red-billed

• White-tailed has a slim, comparatively dainty bill
• Red-tailed has a hefty and long bill, giving it a disproportionately "huge-billed" look
• Red-billed has a mid-sized bill, hefty but not really long, so it looks more "normal" in bill size compared to Red-tailed

The top bird is Red-tailed with a huge, long, hefty bill [#728906 collected 18 Dec 1900 in e. trop. Pacific at 16°N, 115°W]

The middle bird is White-tailed with a slim and comparatively dainty bill [#217073 collected 8 Feb 1927 in the Solomon Is.]

The bottom bird is Red-billed with an intermediate bill; decidedly larger than White-tailed but not as long and massive as Red-tailed [#776556 collected 10 June 1963 at Jamaica Bay, New York, where it was a vagrant.]

All specimens are of female birds. They are also all in an immature plumage, as can be seen when the same specimens are laid side by side (below); all have varying degrees of barring or mottling on the upperparts, especially around the nape and crown. Red-billed is to the left, White-tailed in the center, and Red-tailed to the right:

 
 

This example is both useful and misleading. The comparison is good because it does show the relative size of the birds: White-tailed is small, Red-tailed is huge, and Red-billed is big but a bit smaller than Red-tailed. This example is poor because the birds shown are in different subadult plumages. The tailless Red-billed (lefthand bird) is still in juvenal plumage characterized by the extensive barring from nape to rump and on the upperwing coverts. The other two birds are older is some stage of sub-adult plumage with tail streamers growing. Juvenal-plumaged birds of all species are heavily barred above. Almost nothing has been published about their identification, and I have been unable to review a sufficient series of specimens to come to any conclusions, but it does appear that even juvenal birds show characteristic wing pattern similar to those of the adults. It is said that White-tailed is more coarsely barred than Red-billed in juvenal plumage (Orta 1992) but I cannot confirm that. Please note, however, the black-centered tertials on the big Red-tailed Tropicbird (righthand bird) are conspicuous on this mostly white bird. This character can be useful in some subadults, but it can be very hard to see on birds in the field (e.g., the top two photos on this page). However, even adult Red-tails usually retain a black shaft streak on the tertials.
 

As we have discussed, all juvenal tropicbirds are heavily barred above. A fine example is this Red-tailed Tropicbird photographed off central California: note it is finely barred above from nape through the rump and across the upperwing coverts. This pattern is similar to other juvenal tropicbirds, but this bird is easily identified as a Red-tailed because of its all-white flight feathers (remiges) and because of its disproportionately big bill. You can see the fine black shaft streaks on the outermost primaries but the primaries still look essentially "all-white" and not at all like the primaries of the other two species.

According to Gould et al. (1974), juvenal plumage in Red-tailed Tropicbird is retained for up to 15 months. Unfortunately they do not identify when remex molt begins (primaries are molted from the inner to the outer) but once begun they state that birds molt almost continuously. A second subadult plumage (with spots and vermiculations on an otherwise white birds, perhaps like the specimen shown above) is common over the next 15-16 months. During these months the central tail feathers steadily grow continuously, and bill lightens (from the tip) to yellowish or orange (3rd year) to red (4th year). Individuals do not return to the nesting grounds until four years or older. Adult tropicbirds appear to molt continuously except when actively engaged in nesting (Gould et al. 1974).

Very little has been published on tropicbird identification in juvenal and subadult plumages. Harrison (1983) makes a stab at it but details are in error, including an over-emphasis on the black in the tertials of Red-tailed and illustrating that black as edges to the feathers rather than as dark centers or shaft-streaks (as it is). None of the literature I've seen properly emphasizes the fact that most Red-tailed Tropicbirds encountered far at sea are white-tailed or look "white-tailed." The range of these birds is extensive (Pitman 1986). We have more to learn about these interesting and oh-so-pelagic species.

Photos: All flying White-tailed TropicbirdP. lepturus photos were taken on Cousin I., Seychelles, in Nov 1992. The young Red-tailed Tropicbird P. rubricauda at upper left was taken in the eastern tropical Pacific at 16°N, 148°30'W; the upper right subadult was at 6°26'N, 142°14'W, and the shot from below at about 14°N, 145°30'W; the juvenal Red-tailed (last photo) was offshore San Luis Obispo Co, California, at 34°35'N,122°27'W, on 19 Aug 1992. The top Red-billed TropicbirdP. aethereus was in the eastern tropical Pacific at 4°30'S,84°30'W, and the one photo'd from below was almost on the Equator at 0°30'S, 93°53'W. All photos © D. Roberson; all rights reserved.
 

Literature cited:

Gould, P. J., W. B. King, and G. A. Sanger. 1974. "Red-tailed Tropicbird" in Pelagic Studies of Seabirds in the Central and Eastern Pacific Ocean. Smithsonian Contrib. Zool. 158.

Harrison, P. 1983. Seabirds: An Identification Guide. Houghton Mifflin, Boston.

Orta, J. 1992. Family Phaethontidae (Tropicbirds) in del Hoyo, J., Elliott, A., & Sargatal, J., eds. Handbook of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona.

Pitman, R. L. 1986. Atlas of Seabird Distribution and Relative Abundance in the Eastern Tropical Pacific. NOAA, Nat. Mar. Fish. Serv., Southwest Fisheries Center admin. rpt. LJ-86-02C.

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