1 Bird Art, Monteverde, Costa Rica. robertdean@hotmail.com
2 Cocos Island Scientific Adviser
POBox: 6327-1000 San José, Costa Rica
michelmontoya@correo.co.cr

Resumen

Se presentan observaciones sobre 33 especies de la avifauna de la Isla del Coco, Costa Rica, las que fueron realizadas entre el 25 y 28 de abril del 2005. Se anota el primer registro para la Isla del Coco de Hirundo pyrrhonota (Cliff Swallow / Golondrina risquera), especie migrante neártica.

Introduction

The avifauna of Cocos Island is comprised of 111 species included in 71 genera and 29 families. Of these 32 are pelagic species (15 genera), 39 shorebirds and waders (24 genera), and 40 terrestrial (32 genera). Thirteen species are breeding residents, of which eight are pelagic and five terrestrial including the three species endemic to the island. Ninety-eight migrant species are recorded for Cocos Island and of these 78 are Nearctic migrants of various categories. Of the remaining 20 migrants, 15 are pelagics of wide geographical distribution, four are strictly Neotropical migrants, and one domesticated (Columba livia) (Montoya 2003 updated March 2005, Montoya 2005, Montoya y Pascal 2005).

As of yet the status of these migrant species has not been categorized, (ie. annual, occasional, accidental, etc.), due to a lack of systematic data on the avifauna of Cocos Island. The lack of information regarding dates of sightings, interannual frequency, numbers of individuals and other pertinent data do not allow us a full understanding of the avian dynamics of this island territory.

This article seeks to increase our understanding of this island avifauna while we await the implementation of more systematic monitoring.

These observations were undertaken between 25 and 28 April 2005 while the authors were participating in a program organized by the Organization for Tropical Studies (OTS), aboard the cruiseship Pacific Explorer. They were made while exploring the island’s principal trail system and during circumnavigations in motorized dinghies which allowed us to inspect the coastline and main rocky islets located on the island periphery.

Sula dactylatra

(Masked Booby) (Piquero enmascarado)

Observations: The colony previously described by Montoya (2003) located on the islet Dos Amigos Grande continues to increase, and is now estimated at 20 nesting pairs, including immatures.

Sula nebouxii

(Blue-footed Booby) (Piquero de patas azules)

Observations: One mature adult was seen during the circumnavigation of island on the last evening (28^th). The pale face and upper tail coverts and blue feet were seen clearly. This sighting confirms the accidental presence of this species on the island, as previously recorded only one time (Montoya 2003).

Sula leucogaster

(Brown Booby) (Piquero moreno)

Observations: There are numerous pairs with young nesting principally on clumps of the endemic grass Chloris paniculata, on the islets and rocky outcroppings of the main island in the north, northeast and northwest (Cónica, Manuelita, Pájara, Cáscara y Roca Gissler).

Sula sula

(Red-footed Booby) (Piquero de patas rojas)

Observations: We observed this species nesting in Clusia rosea trees and perching especially on branches of the endemic Cecropia pittieri, on the islets of the north, northeast and northwest of the island. This species also nests in trees on the main island. Downy white nestlings were observed. This is the resident species most heavily preyed upon by the Great Frigatebird (Fregata minor), also a resident species.

Fregata magnificens

(Magnificent Frigatebird) (Rabihorcado magno)

Observations: Several were seen daily, both adults and immatures, soaring amongst Great Frigatebirds. They were observed particularly in the northeast, north and northwest sectors of the island.

Fregata minor

(Great Frigatebird) (Rabihorcado grande)

Observations: Numerous individuals of varying ages were observed daily, mainly in the northeast, north and northwest sectors of the island. In the vicinity of the islets Manuelita, Conica and Pajara they were notably preying upon Red-footed Boobies (Sula sula), as recorded by Slud (1967).

Ardea herodias

(Great Blue Heron) (Garzón azulado)

Observations: One immature was seen on the 26^th on rocks by Wafer Bay and on the 27^th near the bridge over Rio Genio (probably the same individual). The presence of this species on the island was first recorded by Slud (1967) between February and April 1963 at Wafer Bay.

Ardea alba

(Great Egret) (Garceta grande)

Observations: One was seen at Chatham Bay the 26^th and the same day in the afternoon at Rio Genio in Wafer Bay. It was first reported on Cocos Island by Hundley (1962) on 22 May 1962 at Wafer Bay.

Egretta thula

(Snowy Egret) (Garceta nívea)

Observations: One was seen flying across Wafer Bay on the afternoon of the 26^th . Slud (1967) reported various sightings of this species at Wafer Bay during his visit between February and April 1963

Bubulcus ibis

(Cattle Egret) (Garcilla bueyera)

Observations: We observed a group of three in the grass soccer field in front of Villa Beatriz on 26 and 27 April. Sherry & Werner (1984a) reported the first record of this species on the island in March 1980. A history of sightings of this species can be found in Montoya (2004).

Nyctanassa violacea

(Yellow-crowned Night-Heron) (Martinete cabecipinto)

Observations: One immature was seen on the shoreline at Chatham Bay the morning of the 26^th. Another was seen at Isla Cáscara the afternoon of the same day. Slud (1967) recounts the presence of this species on the island, the first record being between 5 and 8 September 1905. It has since been seen on various occasions between the months of January and March.

Falco peregrinus

(Peregrine Falcon) (Halcón peregrino)

Observations: One was seen soaring above Chatham Bay, the afternoon of the 25^th. Slud (1967) remarks on the behaviour of this species on the island .

Charadrius wilsonia

(Wilson’s Plover) (Chortilejo picudo)

Observations: One was observed with a Pectoral Sandpiper at the high tide line, in the west sector of Wafer Bay, on the afternoon of the 26^th. Previously, this species was seen on Cocos Island in the month of September (Slud 1967). There is also a photographic record for the month of January. This bird is always present in limited numbers.

Catroptophorus semipalmatus

(Willet) (Pigüilo)

Observations: A couple were seen on the rocks at the tide line, eastern sector of Punta Presidio, the morning of the 26^th. Slud (1967) presented records of this species on Cocos Island in the months of January, March, June and September, always in small numbers.

Bartramia longicauda

(Upland Plover) (Pradero)

Observations: One was flushed and seen repeatedly on the trail above Chatham in the grass at the edge of the forest, on the morning of the 28^th . The first record of this species on Cocos Island was by Sherry & Werner (1984a), between November 1983 and September 1984.

Calidris melanotos

(Pectoral Sandpiper) (Correlimos pechirayado)

Observations: One was seen with a Wilson’s Plover at the high tide line, in the west sector of Wafer Bay, the afternoon of the 26^th. The first record of this species on the island was by Slud (1967) in April 1963.

Larus atricilla

(Laughing Gull) (Gaviota reidora)

Observations: One immature was seen at Chatham Bay on the 26^th. This species was first recorded on the island in February 1963 (Slud, 1967); these were two specimens in winter plumage. Since 1988 there have been numerous photographic records of this species, always in first or second year plumage.

Larus pipixcan

(Franklin’s Gull) (Gaviota de Franklin)

Observations: One mature breeding adult was seen on the coastline at Wafer Bay on the 26^th. There is only one previous record, by Slud (1967) on 23 April 1963 at Wafer Bay.

Anous minutus

(Black Noddy) (Tiñosa negra)

Anous stolidus

(Brown Noddy) (Tiñosa común)

Observations: Individuals of both species were observed during circumnavigations of the island. We saw them roosting on islets and rocks without vegetation and on various occasions flying and foraging in coastal waters. Hundley (1962) and Slud (1967) made extensive reviews of the presence and behavior of these species on the island.

Gygis alba

(White Tern) (Charrán blanco)

Observations: We made numerous sightings of adults and immatures both along the island’s trail system as well as during circumnavigation. These birds deposit their eggs on natural depressions in the branches of the palm Euterpe precatoria without the aid of nesting material. The presence of this species on the island is from the end of February until the middle of September. Slud (1967) made a series of observations of this species on the island.

Coccyzus ferrugineus

(Cocos Cuckoo) (Cuclillo de la isla del Coco)

Observations: One was seen briefly but well on Chatham-Wafer trail above Wafer Bay on the 26^th. A Pair were seen and observed at close range at the beginning of Chatham trail, for at least 10 minutes on morning of the 28^th. Slud (1967) remarks on observations of this endemic species.

Nesotriccus ridgwayi

(Cocos Flycatcher) (Mosquerito de la Isla del Coco)

Observations: Several were seen on each day, in the Chatham and Wafer Bays areas. They responded well to high whistles. There have been various publications on the behavior of this island endemic (Koodsma et al.1987, Layton 1984, and Sherry 1985, 1986).

Tyrannus tyrannus

(Eastern Kingbird) (Tirano norteño)

Observations: One was seen at the entrance to the forest above Chatham Bay on the morning of the 28^th. This species was first collected on the island by Percy Howe at Wafer Bay on 15 November 1932 (Slud, 1967).

Riparia riparia

(Bank Swallow) (Golondrina ribereña)

Observations: A group of 12 was viewed flying above the exposed grass part of the trail above Chatham Bay continuously on the 25^th , 26^th and even on the 28^th . It was first recorded on the island 21 April 1963 by Slud (1967).

Hirundo rustica

(Barn Swallow) (Golondrina tijereta)

Observations: Two were seen in company each day with Bank Swallows. It was first recorded on the island by Edward Gifford on 5 September 1905 (Slud 1967).

Hirundo pyrrhonota

(Cliff Swallow) (Golondrina risquera)

Observations: One was seen clearly each day in the company of the other swallows. It was easily identified by its square tail, buffy rump, streaked back, pale forehead and chestnut face and throat. This is the first record of this species for Cocos Island.

The Cliff Swallow is a species that reproduces in the north, from Alaska and the Yukon territory, throughout Canada and the western U. S. and Mexico. During the northern winter, it migrates to summering locations in southern South America, especially Argentina, Chile, Uruguay, Paraguay and southern Brazil. Undoubtedly, the birds seen on Cocos Island had detoured from their northward migration route.

In December 2002, the second author, (MM) observed a series of dead swallows on the roof of Villa Beatríz in Wafer Bay beneath a cable which served as their perch. Their death was presumably due to starvation, as Cocos Island offers very little diversity in flying insects, their staple diet. It is possible that the island acts as a nutritive ‘Black Hole’ for many visiting birds that arrive already weak and perish due to lack of food.

Dendroica petechia aureola

(Yellow Warbler) (Reinita amarilla)

Observations: Several (male and female) were seen throughout the trip, especially around the vegetation close to tide line on Chatham and Wafer Bay. Slud (1967) reported observation records of this species after his visit to the island in 1963.

Pinaroloxias inornata

(Cocos Finch) (Pinzón de la Isla del Coco)

Observations: This species was found in all habitats of the island, both adults and juveniles. Noteworthy is the abundance of young birds in the vicinity of the Chatham Bay station. Undoubtedly this is due to the feeding of these birds by both park employees and visitors. The future of this specific population (around the ranger station) therefore must be considered doubtful. There are studies on the population of this species, amongst which we cite: Montoya (1991), Sherry & Werner (1984b), Smith & Sweatman (1976), Werner & Sherry (1987).

Spiza americana

(Dickcissel) (Sabanero arrocero)

Observations: One breeding adult was seen on the 25^th, 26^th, and 28^th in the grassland above Chatham Bay. This species was observed previously on the island by Sherry & Werner (1984a), between November 1983 and September 1984.

Dolichonyx oryzivorus

(Bobolink) (Tordo arrocero)

Observations: A group of five males in breeding plumage foraging in grass at the soccer field in front of Villa Beatriz, Wafer Bay, was seen on 26 and 27 April. The first sighting of this species dates from April 1930 (Chapin cited by Slud 1967), later by Slud (1967), Grant & Grant (1997) and others.

Icterus galbula

(Baltimore Oriole) (Bolsero Norteño)

Observations: One male was seen at the soccer field at Wafer Bay on the afternoon of the 26^th . There is no doubt as to the identification of this bird, as the black head, diagnostic of the male of the species, was seen clearly. Two females were sighted previously at Wafer Bay between 19 and 21 April 1963 by Slud (1967).

Icterus pectoralis

(Spotted-breasted Oriole) (Bolsero pechimanchado)

Observations: This species was seen and heard various times at Wafer Bay between 25 and 28 April by park guards and other observers (Robert Chaverri, 2005). They observed an adult and three immature birds in characteristic plumage in the vicinity of Villa Beatriz. These observations, referring to a species which, introduced on the island in 1954 (Madrigal, 1954) and once considered extinct, now continues to thrive and reproduce on the island.

Bibliography