Browsing by Autor "Douglas J. Levey"

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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.
Evolutionary ecology of pungency in wild chilies
(National Academy of Sciences, 2008) Joshua J. Tewksbury; Karen M. Reagan; Noelle J. Machnicki; Tomás A. Carlo; David C. Haak; Alejandra Lorena Calderón Peñaloza; Douglas J. Levey
The primary function of fruit is to attract animals that disperse viable seeds, but the nutritional rewards that attract beneficial consumers also attract consumers that kill seeds instead of dispersing them. Many of these unwanted consumers are microbes, and microbial defense is commonly invoked to explain the bitter, distasteful, occasionally toxic chemicals found in many ripe fruits. This explanation has been criticized, however, due to a lack of evidence that microbial consumers influence fruit chemistry in wild populations. In the present study, we use wild chilies to show that chemical defense of ripe fruit reflects variation in the risk of microbial attack. Capsaicinoids are the chemicals responsible for the well known pungency of chili fruits. Capsicum chacoense is naturally polymorphic for the production of capsaicinoids and displays geographic variation in the proportion of individual plants in a population that produce capsaicinoids. We show that this variation is directly linked to variation in the damage caused by a fungal pathogen of chili seeds. We find that Fusarium fungus is the primary cause of predispersal chili seed mortality, and we experimentally demonstrate that capsaicinoids protect chili seeds from Fusarium. Further, foraging by hemipteran insects facilitates the entry of Fusarium into fruits, and we show that variation in hemipteran foraging pressure among chili populations predicts the proportion of plants in a population producing capsaicinoids. These results suggest that the pungency in chilies may be an adaptive response to selection by a microbial pathogen, supporting the influence of microbial consumers on fruit chemistry.
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 (<i>Tyrannus</i>) 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.
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.
Where did the Chili Get its Spice? Biogeography of Capsaicinoid Production in Ancestral Wild Chili Species
(Springer Science+Business Media, 2006) Joshua J. Tewksbury; Carlos Manchego; David C. Haak; Douglas J. Levey