Bird Community Differences in Mature and Second Growth Garúa Forest in Machalilla National Park, Ecuador
Total Page：16
File Type：pdf, Size：1020Kb
ORNITOLOGIA NEOTROPICAL 16: 297–319, 2005 © The Neotropical Ornithological Society BIRD COMMUNITY DIFFERENCES IN MATURE AND SECOND GROWTH GARÚA FOREST IN MACHALILLA NATIONAL PARK, ECUADOR C. Dustin Becker1 & Ana Ágreda Earthwatch Institute, 3 Clock Tower Place-Suite 100, P.O. Box 75, Maynard, Massachusetts 01754, USA. CECIA (Corporación Ornitológica del Ecuador), Joaquín Tinajero E-305 y Jorge Drom, Quito, Ecuador. Resumen. – Diferencias entre las comunidades de aves de bosque de garua maduro y secundario en el Parque Nacional Machalilla, Ecuador. – Las estrategias de conservación a nivel de los ecosiste- mas son más eficaces si consideran el grado de sensibilidad que presentan los organismos frente a la per- dida o el cambio estructural de su hábitat. Este estudio presenta información sobre las comunidades de aves del bosque húmedo de la región Tumbesina del Ecuador y, compara mediante el uso de redes de neblina y observación directa, la composición de aves presentes en bosque de garúa maduro y secundario dentro del Parque Nacional Machalilla (PNM). En este estudio registramos 159 especies de aves durante las épocas seca y lluviosa de 1999 & 2000. Realizamos un esfuerzo total de muestreo de 1950 h de capturas con redes y capturamos 729 individuos pertenecientes a 85 especies. Alrededor del 60% de las especies capturadas en redes de neblina dentro de uno u otro tipo de bosque no se hallaban compartidas. La riqueza de especies fue mayor en bosque secundario y se sugiere algunas razones autoecológicas: 1) presencia de especies dependientes de bosque maduro ausentes en bosque secundario, 2) especies insectívoras genera- listas prefieren bosque secundario, y 3) especies migratorias prefieren habitats marginales secundarios. Tres especies de aves endémicas y amenazadas, Hylocryptus erythrocephalus, Leptotila ochraceiventris y Lathrotriccus gri- seipectus fueron registradas frecuentemente en bosque secundario y no en bosque maduro. La riqueza de especies pertenecientes a los géneros de hormigueros fue mayor en bosque maduro, y estuvo relacionada con la abundancia de artrópodos. Diecisiete especies se registraron únicamente en bosque de garúa maduro, pero ninguna se halla dentro de alguna categoría de amenaza. Entre las mas importantes podemos destacar, Gymnopithys leucaspis, Sclerurus guatemalensis y Turdus daguae. La alta detectabilidad de estas especies dentro del bosque sugiere su uso como especies indicadoras de bosque de garúa, el mismo que se halla en peligro de extinción. Abstract. – Species monitoring for conservation planning is aided by understanding species’ sensitivities to habitat change or loss. We studied bird communities in garúa forest, a type of low elevation tropical cloud forest in western Ecuador and Peru that is threatened by land conversion. We used mist-nets and strip counts to compare bird communities in second growth and mature garúa forest at Machalilla National Park, Ecuador. During the two wet and two dry seasons of 1999 and 2000, we recorded 159 bird species. In 1950 h of mist netting, we captured 729 individuals of 85 species. Over 60% of the species were unique to either second growth or mature forest. Species richness of birds was greater in second growth than in mature garúa forest for reasons apparently unrelated to abundance or diversity of food resources. Generalist insectivore species, dry forest endemic birds, and Neotropical migrants readily used second growth forest, while mature garúa forest species were absent or significantly less abundant. Three endemic and endangered species, Henna-hooded Foliage-gleaner (Hylocryptus erythrocephalus), Ochre-bellied Dove ______________ 1Current address: P.O. Box 1248, Zuni, New Mexico 87327, USA. E-mail: [email protected] 297 BECKER & ÁGREDA (Leptotila ochraceiventris), and Gray-breasted Flycatcher (Lathrotriccus griseipectus) were found in second growth more often than in mature forest. Antbird species richness and abundance was greater in mature garúa for- est, than in second growth, possibly due to differential arthropod abundance in forest litter. Seventeen bird species were only encountered in mature garúa forest and none were threatened. Among them, Bicolored Antbird (Gimnopithys leucaspis), Scaly-throated Leaftosser (Sclerurus guatemalensis), and Dagua Thrush (Turdus daguae) were easy to detect by sight or song, making them good indicator species for this type of tropical forest. Birds detected by observation and listening were similar in both forest types making trail surveys less useful than mist netting for detecting differences between bird communities in the two forest types. Accepted 4 March 2005. Key words: Tropical forest conservation, garúa forest, indicator species, endemic birds, western Ecuador, secondary forest, mature forest. INTRODUCTION forests that obtain moisture from clouds, these forests strip moisture from oceanic In addition to studying the last primary forest mists and fog (Becker 1999). Regional botani- patches in the Neotropics, ornithologists are cal experts refer to this type of vegetation as trying to determine the value of human-mod- garúa forest (Elao 1996). Garúa forests have ified lands and second growth habitats for physiognomically typical cloud forest vegeta- bird conservation (Petit & Petit 2002). Since tion (dense loads of vascular epiphytes and the 1950’s, 95% of the primary forest in west- bryophytes on tree branches and trunks) and ern Ecuador has been converted to pasture, occur as low as 400 m (Parker & Carr, 1992). crops, and second growth forest (Dodson & Described by Chapman (1926), Best & Gentry 1991). Elsewhere in the Neotropics, Kessler (1995), and Stattersfield et al. (1998), such rapid change in land cover caused major garúa forest in the Colonche Hills are domi- declines and extirpations of birds (Kattán et nated by tree genera such as Beilschmiedia, al. 1994, Stratford & Stouffer 1999, Estrada et Rheedia, Ocotea, Gleospermum and Quararibea al. 2000). With a baseline understanding of (Elao 1996). what species avoid second growth and prefer Garúa forests are used by a wide variety of mature tropical forest, we can better predict birds in western Ecuador, including 22 the future composition of bird communities species of hummingbirds, 79 regionally in tropical forests, evaluate the success of res- endemic species, and 15 species listed as toration efforts, and possibly thwart further threatened and near-threatened (Becker & extinctions via habitat preservation. In this Lopéz-Lanús 1997). Also, microclimate dif- paper, we compare the composition of bird ferences between leeward and windward communities in mature and second growth slopes of garúa forest can strongly define bird “garúa” (fog and mist) forests in Machalilla communities at a local level (Becker 1999). National Park, in the Tumbesian Endemic Still, little is known about the community of Bird Area (EBA) of Ecuador, an area of sig- birds in mature garúa forest, relative to sec- nificant importance for 55 restricted-range ond growth garúa forest and no research on bird species (Stattersfield et al. 1998, Birdlife avian sensitivity to forest degradation has International 2003). been conducted in this type of tropical forest. Along isolated and patchy mountain In this study, we address three questions: 1) ridges of the Tumbesian region, a humid for- Does bird species composition in mature est similar to high elevation Andean cloud garúa forest differ substantially from that in forest exists. However, unlike Andean cloud second growth garúa forest? 2) What factors 298 BIRD ASSEMBLAGES IN GARÚA FORESTS influence species richness in mature versus species richness is greater where food and second growth garúa forest? and, 3) What cover resources (fruits, flowers, insects, and bird species unique to or abundant in mature woody understory) are most abundant and garúa forest could be good indicators of this variable. habitat type? Finally, for conservation work, the pres- Species richness of birds might be ence of certain bird species can be useful indi- expected to be greater in mature than second- cators for evaluating forest condition (Karr ary garúa forest, because mature forests are 1982, Stotz et al. 1996). Good indicator spe- taller and have more vertical heterogeneity cies are unique, or common in a particular than second growth forests (Rice et al. 1984). habitat, are easily detected in that habitat, and The number of migrant and resident bird spe- show high sensitivity to degradation, fragmen- cies has been found to increase with vertical tation, or loss of a particular habitat (Stotz et foliage diversity (Greenberg 1996), and al. 1996). Avian indicators have been mature forests offer greater potential for described for forty-one principal habitats in niche diversification (Hutchinson 1959, the Neotropics (Stotz et al. 1996), but not for Schoener 1986). On the other hand, species garúa forests of the Tumbesian endemic bird richness has generally been found to be area (EBA). greater in successional habitats than in climax ones because of the variety of generalists spe- METHODS cies attracted there (Ambuel & Temple 1983, Warkentin et al. 1995, Grey et al. 1998). We Study area. Machalilla National Park (hereaf- predict that bird communities in both mature ter, Machalilla) is located in Manabi Prov., and second growth forest patches on Cerro Ecuador, and encompasses an area of 55,095 San Sebastián will both be dominated by ha including La Plata Island and the ocean wide-spread generalist bird species, because surrounding it. Machalilla was