Proposal (310) to
Add Chroicocephalus (formerly Larus) ridibundus (Common Black-headed Gull) to main list
Effect on South American CL: This transfers a species from our Hypothetical List to the Main List.
Background: The Hypothetical List currently reads as follows: "Sight records and unpublished photos from Trinidad & Tobago (Fisher 1978, ffrench & White 1999), Surinam (Davis 1979), Bonaire (Voous 1983, 1985; photograph examined by Voous), and French Guiana (Tostain 1992). Photos now published in Kenefick & Hayes (2006)."
Published photographic record from Tobago: I took numerous photographs of an alternate plumaged adult between Store Bay and Pigeon Point, Tobago, during 4-14 July 1994. I sent my best photos to Claudia Wilds for confirmation, but unfortunately she passed away without having written back to me and the fate of the photos is unknown. Details of the record were published by Hayes (1996) and it was accepted by the Trinidad and Tobago Rare Bird Committee, which had access to the photos (TTRBC 1996-5). One of the photos, now published by Kenefick and Hayes (2006), reveals a gull with a chocolate brown (visible in pdf file but not printed version) hood. The Brown-hooded Gull (L. maculipennis) of southern South America is similar, differing primarily in its molt cycle and by having white rather than black tips to the primaries. The worn wingtips of this particular individual were nearly all white, with only a minute black speck (1-2 mm long) at the tip of the outermost three primaries and a subapical black spot (about 5 mm long) present only on the leading edge (outer vane) of the outermost primary. Although this particular individual superficially resembled a Brown-hooded Gull, the presence of worn alternate plumage in July indicates the bird was on a Northern Hemisphere molt cycle, and therefore a Common Black-headed Gull.
HAYES, F. E. 1996. Noteworthy bird records for Trinidad & Tobago, 1993-1994. Living World, Journal of the Trinidad and Tobago Field Naturalists' Club 1995-1996:20-21.
HAYES, F. E., AND G. WHITE. 2000. First report of the Trinidad and Tobago Rare Bird Committee. Living World, Journal of the Trinidad and Tobago Field Naturalists' Club 1999-2000:39-45.
KENEFICK, M., AND F. E. HAYES. 2006. Trans-Atlantic vagrancy of Palearctic birds in Trinidad and Tobago. Journal of Caribbean Ornithology 19:61-72.
Floyd Hayes, Sept. 2007
Addendum from Remsen 29 Jan. 08: "Alexandre Renaudier has pointed out to me that there are published photos from French Guiana (that we overlooked) in Tostain and Dujardin (1989)."
TOSTAIN, O., AND J. L. DUJARDIN. 1989. Mise en place d'une aire d'hivernage neotropicales de Laridés holarctiques: Larus pipixcan, Larus ridubundus et Larus fuscus. Alauda 57: 189-215.
Comments from Robbins: "YES to all four new records for South America. Identifications appear straightforward and I see no issues concerning provenance."
Comments from Nores: "YES, pero con las restricciones marcadas en Ardea purpurea y Tringa glareola. La foto de Kenefick & Hayes (2006) muestra una especie muy similar a maculipennis y el detalle señalado de que el plumaje de la punta del ala está gastado y por eso aparece casi blanco, es un poco especulativo. Sin embargo, hay un detalle no marcado por Hayes que las distingue fácilmente: el gris de alas y lomo es mucho más oscuro (como aparece en la foto) que en maculipennis. Además, la posibilidad de que maculipennis llegue a Trinidad y Tobago, es muy poco probable."
Comments from Jaramillo: "YES- I like the fact that it is in alternate plumage and coming out of it in July, that fits the northern taxon. The primaries in the photo cannot be used to differentiate between ridibundus and maculipennis, as the Atlantic form of maculipennis has dark tips to the primaries. Only the Patagonian - Pacific form of maculipennis has entirely white primary tips. Structurally the bird also looks longer legged than maculipennis. Also ridibundus is the expected one in Trinidad and Tobago, based on nearby records of small hooded gulls, I have even seen this species myself in the Lesser Antilles."
Comments from Zimmer: "YES. I agree with the ID and Alvaro's diagnosis regarding separation of ridibundus from maculipennis is right on."
Comments from Stiles: "YES. In view of the published photos, I see no problem with adding this species to the SACC list."