THE EUPHONIA Quarterly Journal of Mexican Avifauna Editor: Kurt Radamaker Associate Editors: Michael A. Patten, Deb Davidson• Spanish Consultant: Luis Santaella Consultant: Steve N.G. Howell Proofreaders: Richard A. Erickson, Bob Pann Circulation Manager: Cindy Ludden For an annual subscription to The Euphonia, please send 15.00 dollars U.S. payable to The Euphonia P.O. Box 8045, Santa Maria, California, 93456-8045, U.S.A. Checks drawn on Bancomer in Pesos accepted. The Euphonia encourages you to send in manuscripts. Appro- priate topics range from recent sightings to scientific studies of Mexican birds. Feature articles in Spanish are encouraged. Please send manuscripts, preferably on diskette written in Wordperfect (although almost any major word processor file will suffice), to Kurt Radamaker, P.O. Box 8045, Santa Maria, California 93456, U.S.A. Please send summaries for Recent Ornithological Literature to Michael A. Patten at P.O. Box 8561, Riverside, California, 92515-8561, U.S.A. Recent sightings (with details) should be sent to Luis Santaella, 919 Second St., Encinitas, California 92024, U.S.A. I thank Sophie Webb for the beautiful cover illlustration, and Ed Berresi and his staff at Reprox for the generous donation of the production of the cover. Contents 1 THE BIRDS OF ISLA HOLBOX, MEXICO Steve N.G. Howell and Stuart Johnston 19 NEW RECORDS OF HAWK-EAGLE FROM GUERRERO MEXICO Sophie Webb and Steve N.G. Howell 22 A "BLUE-HEADED" SOLITARY VIREO FROM BAJA CALIFORNIA Gene Anderson 23 RECENT ORNITHOLOGICAL LIT- ERATURE Michael A. Patten THE EUPHONIA Volume 2, Number 1, Spring 1992 THE BIRDS OF ISLA HOLBOX, MEXICO STEVEN. G. HOWELL, Point Reyes Bird Observatory, 4990 Shoreline Highway, Stinson Beach, California 94970 STUART JOHNSTON, 5236 Kirkwood Place N. , Seattle, \Vashington 98103 Isla Holbox lies 10-11 km off the northeast tip of the Yucatan Peninsula, Mexico, from which it is separated by a shallow muddy sound. Paynter ( 19 55) summarized bird records from Isla Holbox up to that time and the only subsequent records from the island are a few ofHowell' s observations includedbyOmateta/. (1989). Duringtheautumnofl984,Howell visited Holbox during 23-26 September and 23-30 November and observed birds in the Gulf of Mexico a few kms off the island on 3-4 February 1982. Johnston visited the island during 12-24 April 1987. Bird observations from these trips provide a preliminary description ofthe island's avifauna. Isla Holbox is 19 km long by up to 1 km wide and aligned roughly east-west , parallel to the mainland coast. Most of the island is covered by effectively impenetrable mangroves and scrub. Observations were thus restricted to the vicinity of the small fishing village ofHolbox, toward the western end of the island, whence several trails originate into the scrub and mangroves. Many species, notably North American migrants, oc- curred only in and around town, probably due to the greater diversity of vegetation, inclu,ding palm groves, bananas, papayas, and citrus trees. Dredging off the dock at the south (inland) side of town provided spoil The Euphonia 2: 1-18, 1993 The Birds ofIsla Holbox banks that added to the attraction of the sound for several water birds. Unlike the somewhat muddy south shore, the north shore comprised of fine white sand beaches. An accessible stretch ofbeach, about 2 km long, extended east from the village. In September 1984, the weather was hot and humid (daily temperatures 25-30° celsius) and observations primarily were restricted from dawn to mid-morning and again in late afternoon; clouds regularly built up during the day but dispersed at night to leave dawn clear. A light wind blew constantly from just north of east, and brief but torrential showers occurred around dawn on 24 and 26 September. November 1984 temperatures were more pleasant, tending to cool with the passage oftwo Nortes (southward-bound cold fronts), one of which brought periods of driving rain and 40-50 krnlh winds on 28-29 November. In April1987 the weather was hot and humid, similar to September, with occasional showers suggesting the passage of weak cold fronts. Paynter (1955) recorded 60 species from Isla Holbox: most that he.collected or observed there in December 1950, and another 23 species from the island based solely on specimens collected by G. F. Gaumer (originally reported by Salvin 1888, 1889; Sclater and Shelley 1891). Parkes ( 1970) has shown, however, that ''data on Gaumer specimens are notoriously unreliable'' and so we suggest that Holbox records based solely on Gaumer specimens should be considered hypothetical. While some Gaumer records may be correct (e.g., North American migrants) several are clearly or probably in error, notably Roadside Hawk (Buteo magnirostris gracilis, the race endemic to Isla Cozumel), Smooth-billed Ani (Crotophaga ani), Black Catbird (Dumetellaglabrirostris), Yucatan Vireo (Vireo magister), and Bananaquit (Coereba jlaveola). These species are typical of islands off the Caribbean coast of the Yucatan Peninsula, particularly Isla Cozumel. The affinity ofHolbox, however, is closer to the mainland. For example the resident Yellow-faced Grassquit is the mainland race pusilla rather than the Isla Cozumel race intermedius, · and the only typically Caribbean species known from Holbox is the widespread Zenaida Dove, although Caribbean Dove probably also occurs. Paynter (1955) commented on several other doubtful Gaumer records. Howell recorded 104 species during his visits, 80 in September and 81 in November, with 59 common to both visits. Johnston recorded 121 species in April1987. Our observations add 79 species to the island's avifauna, and confirm 12 other species previously known only from 2 The Birds ofIsla Ho/box Gaumer specimens. This brings the total species known from Isla Holbox to 152. Only 21 of the species are confirmed or presumed breeding residents on Isla Holbox: Black and Turkey vultures, Clapper Rail, Rock Dove, Zenaida Dove, Common Ground-Dove, Leptoti/a sp. {probably Caribbean Dove), Mangrove Cuckoo, Groove-billed Ani, Cinnamon Hummingbird, Golden-fronted Woodpecker, Tropical Kingbird, Tropi- cal Mockingbird, Mangrove Swallow, Mangrove Vireo, "Mangrove" Warbler, Northern Cardinal, Yellow-faced Grassquit, Red-wingedBlack- bird, Great-tailed Grackle, and Hooded Oriole. Fourteen others are possible or suspected breeding residents (BR? in the list), and 11 others appear to breed on Holbox and mostly or entirely leave the island in winter (SR and SR? in the list). The remaining species are wintering or transient migrants, non-breedingvisitors and vagrants. While Isla Holbox is not far from the mainland, the intervening water, probably in combination with the island's limited habitat diversity, results in a somewhat depauperate avifauna. For example, on 30 November 1984 around Chiquihi on the mainland opposite, whence the Holbox ferry originates, in a little over an hour Howell recorded 15 presumed resident breeding land birds unknown from Holbox. In the following list an asterisk (*)indicates species previously unrecorded from Isla pound sign (#) indicates species apparently known previously only from Gaumer specimens. BR: breeding resident. SR: breeds but apparently mostly or entirely absent in winter. NBV: non-breeding visitor, some present all-year. WV: winter visitor. TM: transient migrant. February refers to 1982, September and November to 1984, and April to 1987. Systematic List *BROWN BOOBY Su/a leucogaster. Two a few miles off Holbox, 4 February. NBV. 3 The Birds ofIsla Holbox *AMERICAN WHITE PELICAN Pelecanus erythrorhynchus. Seven on 25 November, 4 on 18 April. WV. BROWN PELICAN P. occidentalis. Common, in 1984 maximum 166 on 25 September, in 1987 up to 100/day. In September adults made up about 70o/o ofthe total, but by November, immatures outnumbered adults. Local residents reported the species nests on Holbox (Paynter 1955), although this is not yet confirmed. BR? *DOUBLE-CRESTED CORMORANT Phalacrocorax auritus. In September, post-roost flights of up to 2660 noted. No such flights in November, although up to 2000 birds seen off and along the beach. Up to 200/day in April, most (99o/o) of the 1984 birds were adults. This species breeds on Isla Contoy (B. M. de Montes, pers. com.) and may do so on Holbox. Paynter (1955) reported only Neotropic Cormorant at both locations but his identifications have been questioned (A. R. Phillips, pers. com.). BR? NEOTROPICCORMORANT P. brasi/ianus. Incontrasttothepreced- ing species, only single birds seen on 26 September and 13 April. NBV? *ANHINGA Anhinga anhinga. Singles soared over the island on 25 September and 25 November. WV. MAGNIFICENT FRIGATEBIRD Fregata magni.ficens. Up to 50/day in September and November, up to 15/day in April. Only 1-2 adult males in September, with 4-5 in November. Common NBV. GREAT BLUE HERON Ardea herodias. Up to 10 white morph, and 4 blue morph in September, 7 white and 11 blue in November, and 3 white and 1 blue in April. NBV? GREAT EGRET Casmerodias alba. Up to 25/day in 20 in November, but only singles on five days in April. NBV? SNOWY EGRET Egretta thula. Up to 250/day counted flying to roost in September, common in November, 1 on 13 April, 2 on 17 April. NBV? LITTLE BLUE HERON E. caerulea. Daily roost flight maximum of20 4 The Birds ofIsla Holbox adults, 1 immature in September, 50 (mainly adults) in November, but in April only 1 adult, on 14th. WV. TRICOLORED HERON E. tricolor. Daily roost flight maximum of26 in September, fairly common in November, only singles on 4 days in April. NBV? REDDISH EGRET E. rufescens. Up to 8 dark and 1 white morph in September, 7 dark and 1 white in November, and 3 dark and 1 white in April. NBV? *CATTLE EGRET Bub ulcus ibis. Three on 24 September, 46 in off the sea on 25 September, 20 on 13 April, 1 on 19 April, 6 on 23 April.