Variability Profiles for Line Transect Bird Censuses in a Tropical Dry Forest in Mexico

Abstract

Seasonal and temporal patterns of species diversity and abundance in the avifauna of Chamela, Jalisco, Mexico, were studied in different habitats in the coastal tropical dry forest. Species richness did not differ among three different transects. The number of species was temporally homogeneous. Species diversity was similar for all three transects, but it changed to higher values during the rainy season at arroyo habitats and during the dry season (winter) at disturbed habitats. Population fluctuations observed in the second year of the study suggest that stochastic events such as droughts in this region may influence local population dynamics. Patterns of population fluctuation of resident species are discussed with regard to censusing methods and conservation priorities.Restimen. Se estudiaron 10s patrones estacionales y temporales de diversidad y abundancia de la avifauna de Chamela, Jalisco, Mtxico en distintos habitats de la selva baja caducifolia de la costa. La riqueza de especies no difiere entre transectos y es homogknea temporalmente. La diversidad de especies es similar entre transectos, pero el valor de1 indice aumenta durante la Cpoca htimeda a lo largo de 10s arroyos y durante la Cpoca de secas (inviemo) en las zonas perturbadas. Las fluctuaciones en el tamaiio de las poblaciones observadas durante el Segundo aiio de1 estudio sugieren que eventos estoc&icos coma las sequias en la regiBn pueden afectar la din&mica de las poblaciones a nivel local. Los patrones de fluctuaciones de las poblaciones de especies residentes son discutidos en Grminos de la metodologia usada para censar y en cuanto a su prioridad de conservaci6n. Palabras clave: Diversidad de especies; perfiles de variabilidad; Jalisco; MPxico;jhctuaciones de poblaciones; conservacih. INTRODUCTION in tropical regions (see Karr 1981 and Blake Monitoring temporal changes of avifaunas can 1992). provide invaluable information about factors in-We were interested in determining what facfluencing population dynamics, interactions, tors modify avian behavior, producing fluctuacommunity structure, and conservation. Season-tion in diversity and density of each species al changes in density and number of species have throughout time. In this study, we examined been studied in several temperate avian com-variation in avian numbers and species richness munities (e.g., Best 198 1, Anderson et al. 198 1; over two years at specific sites in a tropical dry for a review see Ralph and Scott 198 I), but rarely forest in western Mexico, and investigate the factors that account for variation. Our study of two of the driest years recorded (M&quez-Valdelamar 1987) suggests that: (1) forest resident spe-I

Relationships Between Bird Species Richness and Natural and Modified Habitat in Southern Mexico

“…Seasonal variation of the avifauna in the present study was similar to that found in other tropical forest regions (Chamela region in Jalisco, Mexico and Maringá in Paraná, Brazil; Ornelas et al, 1993, Krügel & Anjos, 2000 where the species richness was greater from October to November. Our results show that species composition did not differ significantly across the 24 study sites, and similarities of different levels among the sites were common.…”

Testing the importance of nest concealment: does timing matter?

“…If birds select nest sites that provide concealment to decrease the risk of predation, is nest‐site selection based on conditions at the time of nest building or those that will prevail later in the breeding process? For most passerines at our Chamela study site, incubation occurs during the dry season (Ornelas et al 1993). Therefore, even if birds are using cues to select sites that will become more concealed during the rainy season, nest building, egg laying, and incubation take place during the dry season when the foliage provides less concealment.…”

“…In the Pacific lowlands of western Mexico, most passerines associated with dry forest select nest sites, build nests, and start incubation at the end of the dry season when the forest is almost completely leafless (Arizmendi et al 1990, Ornelas et al 1993). Chicks hatch when the rains start (Vega Rivera, pers.…”

Estacionalidad y estructura de la vegetación en la comunidad de anfibios y reptiles de Chamela, Jalisco, México

“…Bersier & Meyer 1994, Pearman 1997, Tilman et al 1997, Kaspari et al 2000. En el caso especifico de la región de Chamela, trabajos previos han encontrado resultados similares al presente estudio, detectándose una mayor riqueza y abundancia de mamíferos en la VA que en el BTC, en especial durante la época de secas (Ceballos 1989, Mandujano & Gallina 1996, Mandujano 1999, Nuñez & Miller 2000, Valenzuela & Ceballos 2000: sin embargo, no fue el caso de las avifauna, probablemente debido a la gran movilidad de las especies, cambios estacionales en la composición de las especies por migración, y debido a su conducta reproductiva (Ornelas et al 1993). Así mismo, en otros ambientes áridos y estacionales, tales como los desiertos, durante la época de secas, la distribución de las especies de reptiles y anfibios se concentra en los arroyos o ecosistemas con menor estacionalidad ambiental, mayor disponibilidad de recursos y mayor complejidad estructural (Baker 1990, McComb et al 1993aDegenhardt et al 1996, Gómez & Anthony 1996.…”