Browsing by Autor "Alex E. Jahn"

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A review of the ecology and conservation of the Andean Flamingo Phoenicoparrus andinus and Puna Flamingo P. jamesi in South America
(Cambridge University Press, 2024) Enrique J. Derlindati; Felicity Arengo; Matias Pablo Michelutti; Marcelo Romano; Heber Sosa Fabre; Enver Ortiz; Omar Rocha; Alex E. Jahn; Mariana Chanampa; Ignacio M. Barberis
Summary There are six species of flamingos in the world, all under pressure from human activities in their wetland habitats. Obtaining global population estimates for flamingos is challenging because of their broad geographical range, nomadic movements, capacity for long-distance flight, and the complexity of international monitoring. Two species, the Andean Flamingo Phoenicoparrus andinus and Puna Flamingo P. jamesi , during key parts of their life cycle, use wetlands in the Andes of South America, where they coexist at various sites. We compiled historical information on population estimates and ecology for these two species and integrated data collected on regional simultaneous censuses to describe population trends, current and emerging threats, and provide recommendations for conservation action. Long-term population trends have been difficult to establish given the unreliability of population estimates prior to the late 1990s. Systematic, regional censuses carried out regularly since 1997 have produced robust population estimates for the Andean and Puna flamingos (most recently, 78,000 and 154,000, respectively) and show populations of both species to be stable and increasing. Increasingly rapid changes in wetlands caused by human activities such as industrial-scale mining in breeding and foraging sites in the high Andes wetlands, and agro-industrial activities in their lowland wintering sites, focused on areas of the highest concentrations of flamingos pose threats to their survival and ability to reproduce. In addition, climate change is projected to reduce wetland habitats and some localised effects have already been detected. Continued research on the ecological drivers of flamingo abundance, movements, and population genetics to understand population structure and dynamics are necessary, as well as the identification of response variables to changing environmental conditions. Interdisciplinary and systems-level approaches in the context of international collaboration in monitoring and conservation planning among a diversity of stakeholders will be required to safeguard flamingo populations and wetland habitats.
Determinants of partial bird migration in the Amazon Basin
(Wiley, 2010) Alex E. Jahn; Douglas J. Levey; Jeffrey A. Hostetler; Ana María Mamani
1. Little is known about mechanisms that drive migration of birds at tropical latitudes. Because most migratory bird species in South America have populations that are present year-round, partial migration (in which only some individuals of a given population migrate at the end of the breeding season) is likely to be common, providing an opportunity to assess proximate mechanisms of migration. 2. Two non-mutually exclusive hypotheses explaining intraspecific variation in migratory behaviour were tested in a Tropical Kingbird Tyrannus melancholicus population in the southern Amazon Basin, where a dramatic dry season decrease in the abundance of insect food for kingbirds may promote migration of some individuals. 3. The Dominance hypothesis predicts sub-dominant individuals migrate at the end of the breeding season and dominant individuals do not, whereas the Body Size hypothesis predicts smaller individuals migrate and larger individuals do not. 4. Based on 4 years of data on individually-marked birds, strong support was found for occurrence of partial migration in the study population. 5. In the best model, the largest males (which are typically older and dominant to younger individuals) had the highest probability of migrating. Younger females (which are the smallest individuals in the population) were also more likely to migrate than other kingbirds, except the largest males. Thus, an individual's probability of migrating was associated with a more complex interaction of size, age and sex than predicted by current hypotheses. 6. These results suggest that determinants of migratory behaviour differ between North temperate and tropical latitudes. Most tests of partial migration theory have been conducted on granivores (e.g. emberizids) or omnivores (e.g. turdids and icterids) at North temperate latitudes, where seasonality is primarily defined by temperature cycles. In tropical South America, however, the most common long-distance migrants are primarily insectivorous (i.e. tyrannids), and seasonality is largely defined by rainfall cycles. 7. We propose a hypothesis based on seasonal food limitation to explain partial migration of primarily insectivorous species in seasonal tropical habitats.
Drivers of clutch-size in Fork-tailed Flycatchers (Tyrannus savana) at temperate and tropical latitudes in South America
(Taylor & Francis, 2014) Alex E. Jahn; Diego T. Tuero; Ana María Mamani; Vanesa Bejarano Alegre; Diego Masson; Eluney Aguilar
Many species of birds exhibit a latitudinal gradient in annual reproductive investment, laying more eggs and producing more nestlings at higher latitudes. However, few studies have evaluated the mechanisms that underlie such patterns and such differences in grassland birds specifically. We monitored nests of Fork-tailed Flycatchers (Tyrannus savana) over two breeding seasons at a tropical site in Bolivia (in 2010–11 and 2011–12) and three breeding seasons at a southern temperate site in Argentina (2010–11, 2011–12 and 2012–13), testing two hypotheses explaining variation in clutch-size among populations: the food-limitation hypothesis and the nest-predation hypothesis. Mean clutch-size and mean brood-size were significantly larger at the temperate study site than at the tropical site. Availability of arthropod food per individual bird was significantly higher at the temperate site. There was no relationship, positive or negative, between rates of nest predation and either clutch-or brood-size, and thus no support for the nest-predation hypothesis. We conclude that food availability explains much of the latitudinal variation in clutch-size in this species. We discuss avenues for future research on the mechanisms underlying geographical variation in the life histories of Neotropical birds.
Ecological determinants ofTyrannusflycatcher nestling growth at north- and south-temperate latitudes
(Oxford University Press, 2018) Diego T. Tuero; Alex E. Jahn; Michael S. Husak; Diane V. Roeder; Diego Masson; Florencia M. Pucheta; Tyler J. Michels; Aaron Quickle; Julián Quillén Vidoz; Marisol Domínguez
An organism's life history strategy is made up of a suite of physiological, behavioral, and ecological traits, which vary at both the interspecific and intraspecific levels in accordance with selective pressures operating on individuals. For birds, 2 primary ecological factors have been proposed to explain intraspecific and interspecific variation in nestling growth: nest predation and food availability. Individual nestling growth rates have important consequences for overall fitness because growth speed could influence subsequent reproductive performance and survival. We studied the relationship between ecological factors (i.e. precipitation level and predation rate) and nestling growth patterns of 2 New World flycatcher species (Tyrannidae) of the genus Tyrannus (Fork-tailed Flycatcher [T. savana] and Scissor-tailed Flycatcher [T. forficatus]) breeding at south-and north-temperate latitudes. We tested the hypothesis that nestling growth rates are driven by nest predation rates and predicted that nestling growth rates would be higher in species experiencing higher nest predation rates. We also tested the hypothesis that nestling growth rates are related to precipitation levels (a proxy for food abundance) and predicted that nestling growth rates would be higher at sites with higher precipitation levels. Growth rate was not associated with predation rate, but it varied with precipitation level, with faster nestling growth rates during wet years for the Scissor-tailed Flycatcher living at north-temperate latitudes. Among species, similar growth rates were found during wet years. These results indicate that, at least as proximate causes, precipitation explains intraspecific and interspecific growth rate variation in Tyrannus species to a larger degree than predation. Additionally, the variation in growth rate we observed between wet and dry years indicates a high level of plasticity in growth rate in this group of insectivorous birds.
Hacia una interpretación mecanística de la migración de aves en américa del sur
(2006) Alex E. Jahn; Douglas J. Levey; Jennifer E. Johnson; Ana María Mamani; Susan Davis
Research to date has demonstrated that bird migration is comprised of highly diverse and plastic behavioural patterns. Our objective is to highlight the importance of studying mechanisms underlying these patterns in austral migrants. We focus on the high incidence of overlap in breeding and non-breeding ranges as a particularly thought-provoking pattern. We then explore the opportunities afforded by partial migration theory to elucidate the mechanisms underlying seasonal range overlap. We propose that a mechanistic understanding of migration in South America will both provide a deeper appreciation of the ecology, physiology and evolution of migratory species in the New World, and improve the scientific foundation for their conservation.
Long-distance bird migration within South America revealed by light-level geolocators
(Oxford University Press, 2013) Alex E. Jahn; Douglas J. Levey; Víctor R. Cueto; Jesús N. Pinto‐Ledezma; Diego T. Tuero; James W. Fox; Diego Masson
Little is known about the timing of migration, migration routes, and migratory connectivity of most of the >230 species of birds that breed at south temperate latitudes of South America and then migrate toward the tropics to overwinter. We used light-level geolocators to track the migration of 3 male and 3 female Fork-tailed Flycatchers (Tyrannus savana) captured on their breeding territories in Argentina. All birds initiated fall migration between late January and late February, and migrated 45 to 66 km day–1 in a northwesterly direction through central South America to either one or two wintering areas. Five individuals first spent several weeks (in April and May) in western Amazonia (mainly Peru, northwestern Brazil, and southern Colombia) before moving east to spend the rest of the non-breeding season in central Venezuela and northern Brazil. One individual occupied primarily one wintering area in eastern Colombia, northwestern Brazil, and southwestern Venezuela. Fall migration took approximately 7–12 weeks to complete and covered a distance of 2,888–4,105 km. We did not analyze spring migration data because of broad overlap with the austral spring equinox. These results are the first data on wintering locations, migration timing, and routes of individual migrant passerine birds that breed in South America. Given the general lack of similar data for practically all migratory birds that breed in South America, geolocator technology has the potential to revolutionize our understanding of how birds migrate—and the threats they face—on South America’s rapidly changing landscape.
Migration timing and wintering areas of three species of flycatchers (Tyrannus) breeding in the Great Plains of North America
(Oxford University Press, 2013) Alex E. Jahn; Víctor R. Cueto; James W. Fox; Michael S. Husak; Daniel H. Kim; Diane V. Landoll; Jesús N. Pinto‐Ledezma; Heather K. Lepage; Douglas J. Levey; Michael T. Murphy
Descriptions of intra-and interspecific variation in migratory patterns of closely related species are rare yet valuable because they can help assess how differences in ecology and life-history strategies drive the evolution of migration. We report data on timing and location of migration routes and wintering areas, and on migratory speed and phenology, of Eastern Kingbirds (Tyrannus tyrannus) from Nebraska and Oklahoma and of Western Kingbirds (T. verticalis) and Scissor-tailed Flycatchers (T. forficatus) from Oklahoma. Eastern Kingbirds primarily departed the breeding site in September, migrating to the Amazon Basin (Bolivia and Brazil), >6,400 km from their breeding site, then used a second wintering site in northwestern South America (Colombia, Ecuador, and Peru) before returning to the breeding site in April. Western Kingbirds left Oklahoma in late July, migrating >1,400 km to northwestern Mexico, then to central Mexico and finally to Central America before returning to Oklahoma in April. Scissor-tailed Flycatchers departed Oklahoma mainly in mid-October, migrating to Central America (El Salvador, Guatemala, Honduras, and Nicaragua), ~2,600 km from the breeding site, remaining there until early April before returning to Oklahoma. Timing of migration appears to be tightly linked to molt. Early departure of Western Kingbirds from the breeding site appears to be timed so that they molt in the Sonoran Desert region during the monsoon, whereas Scissor-tailed Flycatchers remain at their breeding site to complete molt in late summer, when insect prey are abundant. Eastern Kingbirds delay molt until reaching South America where, possibly, abundant fruit supports molt.
Morphological and Genetic Variation Between Migratory and Non-migratory Tropical Kingbirds During Spring Migration in Central South America
(Wilson Ornithological Society, 2010) Alex E. Jahn; Douglas J. Levey; Izeni Pires Farias; Ana María Mamani; Julián Quillén Vidoz; Ben Freeman
We attempted to distinguish spring passage migrant Tropical Kingbirds (Tyrannus melancholicus) from resident conspecifics where they overlap in South America. Migrant males at our Bolivian study site had significantly less tail feather molt and longer wing chords than resident males. Migrant females had significantly longer wing chords, less flight feather molt, and less flight feather wear than resident females. We found no evidence of genetic population differentiation between migrants and residents. We also compared wing chords of migrants and residents to those of breeding kingbirds in breeding populations further south. Wing chords of migrants were more similar to those of breeders from further south than to those of breeders at our study site. An ability to distinguish migrant from resident conspecifics will be critical to understanding migrant winter ecology, migratory routes, and connectivity of migratory populations in South America.
Patterns of austral bird migration in the Bolivian Chaco
(Association of Field Ornithologists, 2002) Alex E. Jahn; Susan Davis; Ana María Saavedra Zankys
Austral migrant birds were banded during austral fall (March–April) and spring (October–November) in the Chaco of Santa Cruz, Bolivia. The Tyrannidae was the most common family captured in terms of number of species and total individuals. The difference in capture numbers between the austral spring and fall seasons was the greatest for the Fuscous Flycatcher (Cnemotriccus fuscatus), although most species exhibited little change among seasons. In terms of numbers of captures across each season, no apparent trends in migratory timing were evident. The Creamy-bellied Thrush (Turdus amaurochalinus) exhibited similar fat class distributions among seasons. Within-season trends showed that in fall Creamy-bellied Thrushes with lower fat levels arrived at the study site earlier than fatter birds. Most migrant species captured were not sexually dimorphic or in breeding condition, so sexing was generally not possible. Our lack of knowledge on habitat use and migratory routes of austral migrants in the Chaco, combined with the current high rate of habitat destruction in the region, makes an understanding of the migratory patterns of these birds important.
Seasonal differences in rainfall, food availability, and the foraging behavior of Tropical Kingbirds in the southern Amazon Basin
(Association of Field Ornithologists, 2010) Alex E. Jahn; Douglas J. Levey; Ana María Mamani; Mirtha Saldias; Angélica Alcoba; María Julieta Ledezma; Betty Flores; Julián Quillén Vidoz; Fabián Hilarion
ABSTRACT Little is known about the relationship between seasonal food availability and the foraging strategies of insectivorous Neotropical birds. We studied a population of Tropical Kingbirds (Tyrannus melancholicus), a primarily insectivorous species, in eastern Bolivia to examine relationships between rainfall, food availability, and foraging strategies throughout the year. Our study site in the southern Amazon Basin was characterized by strong seasonal variation in the abundance of the kingbird's main insect prey (coleopterans and hymenopterans), with reduced abundance during the nonbreeding season which largely overlaps the dry season. Overall, mean search times for insect prey by Tropical Kingbirds during the breeding (96.9 ± 85.6 [SD] sec) and nonbreeding (83.7 ± 91.2 sec) seasons did not differ (P= 0.23). However, during the nonbreeding season, kingbird search times were negatively, but nonsignificantly, correlated with coleopteran abundance (r2= 0.43, P= 0.16) and significantly and negatively correlated with hymenopteran abundance (r2= 0.72, P= 0.03). Although insect abundance differed seasonally, kingbird search times did not, perhaps because kingbirds forage on a greater variety of insects during the nonbreeding season or, during the breeding season, kingbird search times may be influenced by the need to monitor and defend nests as well as constraints on the types of prey that can be fed to nestlings. However, the reduced abundance of their primary insect prey and negative relationships between the abundance of those prey and search times during the dry, nonbreeding season suggest that Tropical Kingbirds in southern Amazonia may be food limited, potentially explaining why some migrate and spend that season elsewhere. Existe poca información sobre la relación entre la disponibilidad de comida por temporada y las estrategias de forrajeo de aves insectívoras Neotropicales. Estudiamos una población de Tyrannus melancholicus, una especie principalmente insectívora, en el este de Bolivia para examinar la relación entre lluvia, disponibilidad de comida y las estrategias de forrajeo a través del año. Nuestro sitio de estudio en el sur de la Cuenca Amazónica fue caracterizado por una fuerte variación entre temporadas en la abundancia de la comida principal de T. melancholicus (coleópteros e himenópteros), con una abundancia mucho menor durante la temporada no-reproductiva, cual generalmente corresponde a la temporada seca. En general, el promedio del tiempo durante la cual los T. melancholicus buscaron insectos durante la temporada reproductiva (96.9 ± 85.6 seg) y no-reproductiva (83.7 ± 91.2 seg) no varió significativamente (P= 0.23). Sin embargo, durante la temporada no-reproductiva, el tiempo de búsqueda de T. melancholicus para comida fue negativamente pero no significativamente correlacionado con la abundancia de coleópteros (r2= 0.43, P= 0.16) y fue significativamente negativamente correlacionado con la abundancia de himenópteros (r2= 0.72, P= 0.03). Aunque la abundancia de insectos varió significativamente entre temporadas, el tiempo de búsqueda de T. melancholicus para comida no varió, posiblemente porque forrajean sobre una variedad de insectos mas alta durante la temporada no-reproductiva, o porque durante la temporada reproductiva el tiempo de búsqueda para insectos podría ser influenciada por la necesidad de monitorear y defender al nido. También podría ser que hay limitaciones sobre los tipos de insectos que puede dar a los pichones. Sin embargo, la reducción en la abundancia de los insectos que come y la negativa relación entre la abundancia de esos insectos y el tiempo de búsqueda para comida durante la temporada seca y no-reproductiva sugiere que los T. melancholicus en el sur de la Amazonía podrían ser limitados por la disponibilidad de comida, posiblemente explicando porque algunos T. melancholicus migran para pasar esa temporada en otro lugar.
Seasonal home range size of tropical kingbird (Tyrannus melancholicus) in the southern Amazon Basin
(University of South Florida, 2010) Alex E. Jahn; Jesús N. Pinto‐Ledezma; Ana María Mamanl; Lucas W. DeGroote; Douglas J. Levey
Towards a mechanistic interpretation of bird migration in South America
(2006) Alex E. Jahn; Douglas J. Levey; Jennifer E. Johnson; Ana María Mamani; Susan Davis
Research to date has demonstrated that bird migration is comprised of highly diverse and plastic behavioural patterns. Our objective is to highlight the importance of studying mechanisms underlying these patterns in austral migrants. We focus on the high incidence of overlap in breeding and non-breeding ranges as a particularly thought-provoking pattern. We then explore the opportunities afforded by partial migration theory to elucidate the mechanisms underlying seasonal range overlap. We propose that a mechanistic understanding of migration in South America will both provide a deeper appreciation of the ecology, physiology and evolution of migratory species in the New World, and improve the scientific foundation for their conservation.