Nesting of Four Poorly-Known Bird Species on the Caribbean Slope of Costa Rica
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124 THE WILSON BULLETIN l Vol. 111, No. I, March 1999 Wilson Bull., 11 l(l), 1999, pp. 124-128 Nesting of Four Poorly-Known Bird Species on the Caribbean Slope of Costa Rica BruceE. Young1~3~4and James R. Zook2 ABSTRACT-We describe the nests of four species the relatively inaccessible habitats of the hu- of birds from the Caribbean slope of Costa Rica. A mid Caribbean slope. The lack of reproductive Great Potoo (Nyctibius grandis, nest previously un- information about these species hinders phy- known from Mesoamerica) nest was nothing more than a crevice in a high branch of a large tree, similar to logenetic studies of the relationships among those reported in South America. A nest of the Torrent avian lineages, studies of intraspecific varia- Tyrannulet (Serpophaga cinerea) was found along a tion, general analyses of reproductive behav- river at 35 m elevation, much lower than previous ior, and the development of management prac- breeding reports for this normally montane species. tices for conserving avian biodiversity. Here Also, we confirm systematists ’ predictions that the we describe the first Mesoamerican nest of the Tawny-chested Flycatcher (Aphanotriccus capitalis), a Great Potoo (Nyctibius grandis), the first low- species of near-threatened conservation status, is a sec- ondary cavity nester. Finally, we report on the second land nest of the Torrent Tyrannulet (Serpo- known nest of the Sooty-faced Finch (Lysurus crassi- phaga cinerea), the first nest of the Tawny- rostris) from montane forest. Received 20 May 1998, chested Flycatcher (Aphanotriccus capitalis), accepted 7 Oct. 1998. and the second nest of the Sooty-faced Finch RESUMEN.-Describimos 10s nidos de cuatro es- (Lysurus crussirostris). pecies de aves de la vertiente de1 caribe en Costa Rica. Un nido de Nyctibius grundis (nido era anteriormente STUDY AREA desconocido en Mesoamerica) era nada mbs que una Our observations were made in the 45,000 ha La grieta en una rama alta de un arbol grande, muy pa- Selva-Braulio Carrillo National Park reserve complex recido a 10s nidos de la misma especie encontrados en in Heredia Province, northeastern Costa Rica. The re- America de1 Sur. Describimos un nido de Serpophaga serve complex, the largest protected elevational tran- cinerea, el cual fue encontrado en un rfo a 10s 35 sect in Central America, extends from montane rain msnm, mucho m&s bajo que 10s otros registros de esta forest surrounding the Barva Volcano at 2,900 m down especie de1 bosque montano. Describimos unas obser- to lowland wet forest at the La Selva Biological Sta- vaciones que indican que el Aphanotriccus capitali.s, tion at 35 m elevation on the Caribbean slope (Timm una especie ligeramente amenazada desde la punta de et al. 1989). vista conservacionista, anida secondariamente en 10s Observations were made in 1997 during routine bird huecos dentro de 10s arboles. Finalmente, presentamos monitoring activities at La Selva (10” 26 ’ N, 83” 59 ’ la segunda descripcidn de1 nido de Lysurus crassiros- W) and at a remote campsite at 1070 m elevation in tris, el cual fue encontrado en un bosque montano. Braulio Carrillo National Park (10” 16 ’ N, 84” 5 W). Annual rainfall at La Selva averages 3962 mm, with a relative dry period between January and March during most years (Sanford et al. 1994). Although precipita- Despite decades of intensive ornithological tion data are scarce for higher elevations, annual rain- study, the nests and eggs of a number of Cen- fall may average over 5000 mm at the 1070-m site, tral American bird species are poorly known where clouds frequently bathe the premontane rain for- (Skutch 1954, 1960; Stiles and Skutch 1989). est in mist (Hartshorn and Peralta 1988). Average can- opy height varies from 28-38 m at La Selva to 22-36 Especially enigmatic are species inhabiting m at 1070 m (Lieberman et al. 1996). 1Organization para Estudios Tropicales, Apartado NEST DESCRIPTIONS AND DISCUSSION 676-2050, San Pedro de Montes de Oca, Costa Rica. Nyctibius grandis.-The Great Potoo is one 2 Apartado 182-4200, Naranjo de Alajuela, Costa of three Central American species of the ge- Rica. nus Nyctibius, the only genus in the exclu- 3 Current Address: Latin America and Caribbean Di- vision, The Nature Conservancy, 4245 North Fairfax Dr., sively Neotropical family Nyctibiidae. Al- Arlington, Virginia 22203; E-mail: [email protected] though difficult to observe in daylight because 4 Corresponding author. it roosts motionless on canopy branches, the SHORT COMMUNICATIONS 125 incubating an egg initially and then brooding a chick, although we could not determine the hatching date. Although collections of adults on eggs in Brazil and observations of N. gri- seus in Costa Rica indicate that males incu- bate during the day (Skutch 1970, Sick 1993), we could not identify the sex of the individual (or individuals) we saw because sexes are similar in outward appearance in Great Potoos (Land and Schultz 1963, Wetmore 1968). No nest was visible and, from our vantagepoint 30 m from the tree and level with the nest, only a slight crevice in the branch was visible. Although the location appeared precarious, re- ports from Brazil suggest that a notch in the nest branch can securely hold an egg (Sick 1993). At a nest in Venezuela, a chick remained FIG. 1. Adult and nestling Great Potoo (Nycribius with its parent for a month, and then alone for grandis) on the branch of a large Hernandia didyman- almost another month before growing to a size tha tree, La Selva Biological Station, Costa Rica, April greater than two-thirds that of the adult and 1997. dispersing (Vanderwerf 1988). This observa- tion suggests that the chick we observed, Great Potoo is readily detectable at night by which never attained half the size of the adult, its characteristic calls (Perry 1979, Slud did not survive. In addition, the wings did not 1979). It ranges from southern Mexico to appear sufficiently developed for sustained southeastern Brazil and central Bolivia (AOU flight. Despite an extensive ground search, we 1998, Howell and Webb 1995). found no evidence of its having fallen from On 5 February, a visitor to the station (K. the nest. The chick may have been taken by McGowan) found a single Great Potoo an arboreal predator such as a monkey (Cebus perched 34 m high on the branch of a 44 m capucinus, Ateles geoffroyi, or Alouatta pal- tall Hernandia didymantha (Hemandiaceae) liatu), tayra (Eiru barbara), or Collared For- tree. The tree was located 500 m inside of old est-Falcon (Micrastur semitorquatus), all growth forest, at the edge of a large treefall common in the area. Even though the attempt gap on a steep hill. The bird was perched on was probably unsuccessful, its daily survivor- an upward sloping section of an S-shaped ship rate in the (presumed) egg and chick branch approximately 20 cm in diameter. stage of 98.7% is substantially higher than the Thereafter on daily visits, we observed a bird 93% rate measured for understory cup-nesting in exactly the same position. birds the same year in the same area (B. On 4 April, we observed for the first time Young, unpubl. data). a fully feathered chick on the branch in front Serpophaga cinerea.-The Torrent Tyran- of the adult. The chick was paler in coloration nulet is a conspicuous resident of highland than the adult and about one quarter the size rivers from Costa Rica to Venezuela and Bo- (Fig. 1). On subsequent days, the chick moved livia (AOU 1998). Their cup-shaped nest at- between a hidden position under the adult’s tached to vegetation above rivers is well breast feathers and the branch immediately in known (Skutch 1960). The elevational distri- front of the adult. The adult remained almost bution of the species is variously described as motionless and never moved along the branch. 250-2500 m in different parts of its range We last saw the birds on 20 April. Despite (Meyer de Schauensee and Phelps 1978, Hilty extensive searches on all neighboring branch- and Brown 1986, Stiles and Skutch 1989, Rid- es in the following days and months, neither gely and Gwynne 1993, Kidgely and Tudor adult nor young was seen again. 1994). The motionless adult we saw was probably We first detected Torrent Tyrannulets on the 126 THE WILSON BULLETIN * Vol. 111, No. I, March 1999 Sarapiqui River in 1994 in Chilamate, 5 km The rectangular hollow was oriented slightly west of La Selva at an elevation of 40 m. In upward, 8 cm deep and 25 X 8 cm wide, 1.5 March 1997, we began seeing individuals m up in the 36 cm dbh tree. The tree was in along the same river where it passes through a small, shady clearing 10 m away from a La Selva at 35 m elevation. These were the small (0.25 ha) patch of second growth forest. first observations of the species in La Selva A local naturalist guide, E. Castro, reported in four decades of ornithological investigation finding an active nest of this species in a hol- (Levey and Stiles 1994). During the first week low section of a 30 m diameter clump of of April, a pair of tyrannulets began construc- Asian bamboo (Guadua sp.) in a patch of sec- tion of a nest 0.5 m above the water level in ond growth forest 2 km north of La Selva. shrub vegetation growing in the middle of a Castro reported seeing adults carrying food to small island in the river, which is approxi- the nest and later feeding a fledgling in the mately 80 m wide and 1 m deep at this point.