Papers by Gabriel Colorado
Successful conservation of rare species requires detailed knowledge of the species' distribut... more Successful conservation of rare species requires detailed knowledge of the species' distribution. Modeling spatial distribution is an efficient means of locating potential habitats. Cerulean Warbler (Dendroica cerulea, Parulidae) was listed as a Vulnerable Species by the International Union for the Conservation of Nature and Natural Resources in 2004. These neotropical migratory birds breed in eastern North America. The entire population migrates to the northern Andes in South America to spend the nonbreeding period. As part of a larger international conservation effort, we developed spatial hypotheses of the bird's occurrence in South America. We summarized physical, climatic, and recent land-cover data for the northern Andes using ESRI software, ArcGIS. We developed five hypothetical distributions based on Mahalanobis D, GARP, Biomapper, MAXENT, and Domain models. Combining results of the different models on the same map allowed us to design a rigorous strategy to ground-t...
Biological Conservation, 2015
Although a growing number of studies address how Neotropical birds respond to anthropogenic distu... more Although a growing number of studies address how Neotropical birds respond to anthropogenic disturbance and deforestation, we continue to poorly understand responses of groups of interacting species, such as mixed-species flocks in the Andes. In this study, we examined how attributes at landscape (i.e., percentage of forest cover within 1-km 2 ) and local (i.e. structural complexity of microhabitat) scales shaped mixed-species flocks within five broadly-defined habitat types in the Northern and Central Andes. From 2007 to 2010, we systematically surveyed flocks along line transects in 97 1-km 2 plots distributed from Venezuela to Peru based on a stratified-random design. We recorded 220 avian species in 186 mixed-species flocks, with the greatest species richness and largest flocks detected in forested habitats. Understory insectivores were most closely associated with mature and secondary forests. Increasing forest cover promoted species richness and size of flocks, with particularly strong associations in successional habitats and shade coffee. Structural complexity was positively associated with flock size in early successional and silvopastoral habitats, where 20% increases in complexity doubled flock size. However, the opposite pattern was true in shade coffee and secondary forests. Encounter rates of flocks were poorly explained by simple metrics of forest cover and structural complexity. Unlike flocks reported in many lowland forests, Andean flocks tended to span all vertical strata, with fewer understory-specializing flocks (e.g. flocks led by Basileuterus warblers and Chlorospingus tanagers). Nonetheless, in such flocks, understory insectivores were most closely associated with mature and secondary forests. Our research supports the idea that managed habitats with overstory trees can contribute to flock conservation. Overall, our results further suggested that understory birds require the more forested of habitats (e.g., mature forest held almost twice as many understory specialists as other habitats), and may be less amenable to conservation with agroecosystems or working landscapes.
The Journal of animal ecology, Jan 5, 2014
The relative contribution of deterministic and stochastic processes in the assembly of biotic com... more The relative contribution of deterministic and stochastic processes in the assembly of biotic communities is a central issue of controversy in community ecology. However, several studies have shown patterns of species segregation that are consistent with the hypothesis that deterministic factors such as competition and niche-partitioning structure species assemblages in animal communities. Community assembly provides a theoretical framework for understanding these processes, but it has been seldom applied to social aggregations within communities. In this research, we assessed patterns of non-randomness in Andean mixed-species flocks using three assembly models: (i) co-occurrence patterns; (ii) guild proportionality; and (iii) constant body-size ratios using data from 221 species of resident and Neotropical migrant birds participating in 311 mixed-species flocks at 13 regions distributed in Venezuela, Colombia, Ecuador and Peru. Significant assembly patterns for mixed-species flocks...
Resumen. -Hallazgos recientes en la distribución invernal de la Reinita Cerulea (setophaga cerule... more Resumen. -Hallazgos recientes en la distribución invernal de la Reinita Cerulea (setophaga cerulea) en los Andes. -Recientes reducciones poblacionales han incitado a la Unión Internacional para la Conservación de la Naturaleza a listar a la Reinita Cerúlea (Setophaga cerulea: Parulidae) como una especie Vulnerable. Se cree que esta disminución puede estar relacionada con la pérdida de hábitat a través de todo su rango, principalmente debida a deforestación y degradación de sus hábitats. En respuesta, miembros de El Grupo Cerúleo, un subcomité del Grupo Técnico de la Reinita Cerúlea encargado de aspectos de la especie en sus cuarteles de invierno, desarrollaron un modelo predictivo de hábitat invernal para la Reinita a través del norte y centro de los Andes. Entre 2006-2010, llevamos a cabo muestreos de campo en Venezuela, Colombia, Ecuador y Perú como parte de un esfuerzo para validar este modelo de hábitat. En este artículo, compartimos nuevos hallazgos sobre la distribución de la reinita cerúlea así como una revisión de análisis recientes acerca del poder de este modelo para predecir su rango invernal. Primero, nuestros datos muestran que la especie ocupa un rango altitudinal más amplio de lo considerado previamente. Segundo, las reinitas cerúleas emplean una variedad mayor de tipos de hábitat, incluyendo diferentes estados sucesionales y agroecosistemas intensamente manejados. Tercero, la especie muestra una fuerte asociación con bandadas mixtas Neotropicales en su mayoría compuestas por especies de aves residentes. Colectivamente, estos hallazgos tienen importantes implicaciones para los esfuerzos de conservación en los Andes.
The descriptive power of morphometric variables of birds on the conformation of food guilds was a... more The descriptive power of morphometric variables of birds on the conformation of food guilds was assessed. Three groups of species were completed based on their morphology separation through Principal Component Analysis. The three groups were associated to three trophic guilds: frugivores, insectivores and nectarivores, the latter presenting the clearest pattern of association. For some species, there was not an evident pattern of association. A high correlation among some morphometric variables was found, suggesting that some measurements are redundant, making possible the choice of a smaller set of variables.
Abstract. – Foraging ecology provides insight into species requirements and focus conservation ef... more Abstract. – Foraging ecology provides insight into species requirements and focus conservation efforts. We studied foraging ecology of the Neotropical migrant Cerulean warbler (Setophaga cerulea) during the winter season in coffee agroforestry ecosystems of the Central and Western Cordillera of the Andes in Colombia. Our findings show that this species is an active foliage gleaner. Cerulean Warbler primarily gleans prey off the upper surface on green leaves and flowers. It frequents shrubs and medium-high trees and forage most often in subcanopy and understory using the outer strata. There were sex differences in the foraging height. Frequently, Cerulean Warbler was encountered in pairs or small groups rather than join in mixed bird flocks. Additionally we documentedteh social behavior and competitive interaction with Setophaga fusca and S. castanea.
Group living is a widespread, ubiquitous biological phenomenon in the animal kingdom that has att... more Group living is a widespread, ubiquitous biological phenomenon in the animal kingdom that has attracted considerable attention in many different contexts. The availability of food and the presence of predators represent the two main factors believed to favor group life. In this review, major theories supporting grouping behavior in animals are explored, providing an explanation of animal grouping. This review is divided in two sections. First, major theories as well as potential mechanisms behind the benefit of grouping are described. Later, a special case on the widespread animal social system of mixed-species avian flocks is presented, exploring the available information in relation to the potential causes that bring birds together into this particular social aggregation.
Journal of Field Ornithology, 2010
ABSTRACT ABSTRACT South of Mexico, little is known about the fall migration patterns of most Neot... more ABSTRACT ABSTRACT South of Mexico, little is known about the fall migration patterns of most Neotropical migrants. I studied the migration of Empidonax flycatchers using mist-net surveys in northwestern Colombia from late September to mid-October in 4 yr (2003–2005, 2008). Empidonax species were identified using linear measurements and color patterns. About 62% of captured individuals were reliably identified to species, with 86% identified as Willow Flycatchers (Empidonax traillii) and 14% as Alder Flycatchers (E. alnorum). No Acadian Flycatchers (E. virescens) were identified. Most birds captured were adults (84.9%) and, due to overlap in measurements, I was only able to determine the sex of 16.3% of the birds. Most Empidonax flycatchers migrated through northwestern Colombia during September and October, with individuals migrating through my study area over a period of at least 1 mo. Willow Flycatchers tended to migrate earlier than Alder Flycatchers, a pattern consistent with the fall movements of these two species at other locations. No captured flycatchers were molting either remiges or rectrices, and most (89%) had either no or slight traces of subcutaneous fat. No Empidonax flycatchers were recaptured, suggesting that stopover duration at my study site was brief. My results show that many Empidonax flycatchers can be identified as Willow and Alder flycatchers during the nonbreeding period, and such identification will enhance our knowledge of their geographical distribution and improve our understanding of possible patterns of segregation on their wintering grounds.RESUMENSe sabe muy poco sobre los patrones de migración de la mayoría de las aves que se mueven al sur de México. Estudie la migración de papamoscas (Empidonax) utilizando redes de niebla para hacer censos en el noroeste de Colombia. El trabajo se llevó a cabo desde tarde en septiembre hasta mediados de octubre durante los años 2003–2005, 2008. Se utilizaron medidas lineales y patrones de coloración para identificar las especies de Empidonax. Un 62% de las aves capturadas se pudieron identificar adecuadamente hasta el nivel de especie. De estos, un 86% resultaron ser individuos de E. traillii, y 14% de E. alnorum. El común E. virescens, no fue identificado. La mayoría de las aves fueron adultos (84.9%) y debido a un solapamiento en las medidas solo pude determinar el sexo del 16.3% de los individuos. La mayoría de los. Empidonax migran a través del noroeste de Colombia durante septiembre y octubre, con individuos migrando sobre el área de estudio durante al menos un mes. E. traillii tiende a migrar más temprano que E. alnorum, lo que es un patrón consistente con los movimientos otoñales de esta especie a través de otras localidades. Ninguna de las aves capturadas estuvo mudando y la mayoría (89%) no tenía grasa subcutánea. Ninguna ave fue recapturada, sugiriendo que el tiempo de estadía en el lugar de estudio es breve. Mis resultados muestran que muchos Empidonax pueden ser identificados como E. traillii y E. alnorum durante el periodo no-reproductivo. Estas identificaciones pueden realzar nuestros conocimientos sobre su distribución geográfica y mejorar nuestro entendimiento de los posibles patrones de segregación en los lugares donde estas especies pasan el invierno.
The tropical Andes are widely recognized as one of the world´s great centers of biodiversity. Hig... more The tropical Andes are widely recognized as one of the world´s great centers of biodiversity. High levels of both species richness and endemism coupled with one of the greatest rates of deforestation among tropical forests have made the Andes a major focal point of international conservation concern. In the face of current and projected rates of deforestation and habitat degradation of Andean forests, persistent large gaps in our understanding of ecological responses to anthropogenic disturbances limit our ability to effectively conserve biodiversity in the region. My dissertation focused on ecology and conservation of two poorly known components of Andean forest bird communities, mixed-species flocks and overwintering Neotropical-Nearctic migratory birds. Specifically, I (1) examined assembly patterns of mixed-species avian flocks, (2) evaluated the sensitivity of mixed-species flocks and Neotropical-Nearctic migratory birds to deforestation and structural changes in habitat, and (3) identified potential physiological consequences of both using shade coffee and flocking to wintering Neotropical-Neartic migratory birds. To achieve this, I evaluated richness and abundance patterns of the community of wintering Neotropical-Nearctic migratory birds and resident mixed-species flocks across a broad geographical area (approximately 200,000 km 2 ) of Northern and Central Andes, ranging from northwestern Venezuela in the Mérida Cordillera (± 10 o S, 70 o W) to northern Peru's Cóndor Cordillera (± 5 o S, 78 o W), and including the Eastern, Central vi DEDICATION A Luciana. Eres el ser más hermoso que he visto en mi vida. Tu existencia cambió la mía, y llena mi corazón. A Yira. Pudiste haber llegado antes o pudiste haber llegado después, pero llegaste en el momento indicado. A Robinson. Lo siento mucho por mi incapacidad de haber hecho lo correcto. Estás siempre ahí. A Alberto. He pasado mucho tiempo tratando de encontrarte. Lo curioso, siempre estás ahí, en mi personalidad, en mis acciones y en mi forma de pensar. A Gloria. El tiempo no nos ayudó, pero te recuerdo tan fuerte como puedo. A Carlos. Me alegra que estés de regreso. Te extrañé mucho. A Eugenia. Todas mis acciones tienen una parte de ti, y soy la continuación de tus pensamientos y deseos. Tu amor por la naturaleza está inevitablemente en mí. vii ACKNOWLEDGMENTS I would like to express my gratitude to my advisor, Amanda D. Rodewald, for her continued support and orientation during the process of this research. We had really productive and enlightening conversations, here in the United States and in many other places. I appreciate her optimism and enthusiasm as well as her interest for ecology and conservation. Thanks for being so patient with me, in particular with my writing in a foreign language. I would like to thank Professors Elizabeth Marschall and Paul Rodewald for serving as members of my committee and for their invaluable suggestions and comments throughout my study. I also would like to thank my colleagues from the acknowledgment to incredible field crews, who constantly demonstrated that the impossible was possible and that we could beat the maldición cerulea: in Venezuela, I am grateful with J. Miranda, D. muñoz, C. Tosta and C. Valeris; in Colombia, I am grateful to E
ORNITOLOGIA NEOTROPICAL, 2008
Notes, Jan 1, 2008
Resumen. -Esfuerzo cooperativo de el Grupo Ceruleo para determinar el rango no reproductivo de la... more Resumen. -Esfuerzo cooperativo de el Grupo Ceruleo para determinar el rango no reproductivo de la Reinita Cerulea en Sur America. -La Reinita CerUlea (Dcndroica ecru/co: Parulidae) ha sido listada como una especie vulnerable por la Uni6n Internacional para la Conservaci6n de la Naturaleza, debido a su reciente reducci6n poblacional. En el 2001 se cre6 el Grupo Tecnico de la Reinita CerUlea como un esfuerzo internacional proactivo para desarrollar estrategias para su conservaci6n. Uno de sus sub comites, El Grupo CerUleo, realiza actividades en sus cuarteles de invierno dirigidas a prom over la protecci6n de esta especie por medio de la conservaci6n de habitats, la investigaci6n de la ecologia de esta ave, campafias de divulgaci6n, y el desarrollo de un modelo predictivo para permitir la evaluaci6n y el monitoreo de la Reinita Cenilea. La mayona de los esfuerzos recientes de este Grupo se han enfocado en el estudio y el entendimiento de la distribuci6n espacial de esta especie en Sur America por medio de modelos predictivos, como una estrategia esencial para el conocimiento de la ocurrencia de esta ave y, de esta forma, identificar habitats importantes y areas de concentraci6n en el Neotr6pico. Para esto, El Grupo CerUleo desarro1l6 cinco modelos hipoteticos de la distribuci6n potencial de la especie en el norte de los Andes basados en registros hist6ricos y muestreos realizados por miembros del mismo grupo. Con el objeto de validar el resultado de la modelaci6n, seleccionamos localidades para verificar la ocurrencia de la especie, basados en un disefio estratificado al azar, las cuales fueron predichas por los cinco modelos. Elaboramos protocolos de campo para muestrear estas localidades. La informaci6n resultante sera analizada empleando tecnicas de modelamiento de ocupaci6n. Se presentaran los disefios basicos para llevar a cabo el muestreo en campo, as! como resultados preliminares del primer afio de estudio.
Forest Ecology and Management, 2007
Detailed ground-based quantifications of total carbon stocks in tropical forests are few despite ... more Detailed ground-based quantifications of total carbon stocks in tropical forests are few despite their importance in science and ecosystem management. Carbon stocks in live aboveground and belowground biomass, necromass, and soils were measured in a heterogeneous landscape composed of secondary and primary forest. A total of 110 permanent plots were used to estimate the size of these carbon pools. Local biomass equations were developed and used to estimate aboveground biomass and coarse root biomass for each plot. Herbaceous vegetation, fine roots, coarse and fine litter, and soil carbon to 4 m depth were measured in subplots. In primary forests, mean total carbon stocks (TCS) were estimated as 383.7 AE 55.5 Mg C ha À1 (AES.E.). Of this amount, soil organic carbon to 4 m depth represented 59%, total aboveground biomass 29%, total belowground biomass 10%, and necromass 2%. In secondary forests, TCS was 228.2 AE 13.1 Mg C ha À1 , and soil organic carbon to 4 m depth accounted for 84% of this amount. Total aboveground biomass represented only 9%, total belowground biomass 5%, and total necromass 1% of TCS in secondary forests. Monte Carlo methods were used to assess the uncertainty of the biomass measurements and spatial variation. Of the total uncertainty of the estimates of TCS, the variation associated with the spatial variation of C pools between plots was higher than measurement errors within plots. From this study it is concluded that estimates of aboveground biomass largely underestimate total carbon stocks in forest ecosystems. Additionally, it is suggested that heterogeneous landscapes impose additional challenges for their study such as sampling intensity. #
Se evaluó el efecto de la presencia de adultos de Jacana spinosa (Aves: Jacanidae) en la frecuenc... more Se evaluó el efecto de la presencia de adultos de Jacana spinosa (Aves: Jacanidae) en la frecuencia de forrajeo de sus juveniles en la estación biológica Palo Verde, Costa Rica. Esta se estimó como el número de picotazos dados sobre el sustrato en un minuto. No se detectaron diferencias en la tasa de picotazos ni para juveniles ni para individuos adultos con la variación de la composición del grupo (juveniles con adultos vs. juveniles solamente). Tampoco se presentaron variaciones en la tasa de forrajeo en el transcurso del día, ni con el tamaño del grupo. Este comportamiento se atribuyó a la avanzada edad de los juveniles en estudio (50-60 días), para los cuales fue indistinto la edad del compañero de bandada, si fuese un adulto o un coetáneo.
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Papers by Gabriel Colorado