Department of Zoology
P.O. Box 118525
University of Florida
Gainesville, FL 32611-8525 USA
phone: 352.392.9169
fax: 352.392.3704
I am interested in the evolutionary ecology of migrant birds: Why have some species evolved migratory habitats and others not? From my way of thinking, migration has been viewed too narrowly by most people. They tend to assume that migration is black-and-white – either a species migrates or it does not. Also, migration is typically assumed to involve substantial distances of travel. Birds that make seasonal movements on small scales are somehow not considered to be migratory. Finally, few researchers study more than one migratory system and lack, I believe, a global perspective.
In short, I think it’s important that people interested in migration take a broad view of it. Migration is not dichotomous trait. Indeed, many species have both migratory and non-migratory individuals even within the same population. These “partial” migrants are especially common in the austral migration system and may represent a key step in the evolutionary pathway to migration. Unfortunately, they are poorly understood and practically unstudied. Ornithologists in South America can make a major contribution to this area. For more information about partial migration, see Alex Jahn’s link on this website.
A second way in which ornithologists can take a broader view of migration is by considering the entire spectrum of migratory movements, from those that take place on small scales (altitudinal or regional) to those that take place on large scales (continental). What typifies species that migrate small distances versus those that migrate long distances? How are both types different from species that do not migrate at all? Similarities and differences to be considered should include behavioral, morphological, and ecological traits. All should be placed in a phylogenetic context.
Finally, ornithologists can broaden themselves by collaborating with colleagues who work in different regions and have different skills and experience. As explained elsewhere on this website, this was the central motivation for the symposium on austral migration at the Neotropical Ornithological Congress. And, it’s what we hope this website will help accomplish. Theories developed for migratory systems in the Northern Hemisphere can be applied to the Southern Hemisphere, providing a largely independent test of those theories. (Testing a theory on the system that generated it is circular; to make true progress, theories generated on one system should be tested on another.) For an example, see Chesser and Levey 1998, American Naturalist). In the same way, methodologies that have been developed and perfected on migratory birds in the Northern Hemisphere are ripe for application to austral migrants. Opportunities abound! All North American contributors to this website have expressed a keen interest in helping South American colleagues apply methodologies; they want to collaborate. Needless to say, everyone will benefit. And ultimately, migratory birds will benefit, too.
To the left are links to some of my publications on the evolutionary ecology of migratory birds. Here is a synopsis of each:
Levey, D.J. 1988. Spatial and temporal variation in Costa Rican fruit and fruit-eating bird abundance. Ecological Monographs 58:251-270.
This represents some of my dissertation research, done in Costa Rica. The take-home message is that the bird community of a lowland rain forest is surprisingly dynamic. In addition to Neotropical migrants that appear and disappear from many habitats, altitudinal and intra-tropical migrants come and go. Some species are partial migrants and others shift habitats, “migrating” at the scale of hundreds of meters. Many of these movements are linked to shifts in the abundance of fruit.
Levey, D. J. and F. G. Stiles. 1992. Evolutionary precursors of long-distance migration: resource availability and movement patterns in Neotropical landbirds. American Naturalist 140:447-476.
This paper reviews the scales over which migration occurs in North and Central America, then proposes a hypothesis for the evolution of migration. In short, it suggests that species with small scale movements within the tropics were evolutionary predisposed to developing large scale movements out of the tropics. These species tend to be those that depend on highly seasonal resources (fruits and flowers, in particular) and/or live in highly seasonal environments (dry forests, and “open” habitats).
For an abridged version of this paper in Spanish, see Levey, D. J. and F. G. Stiles. 1994. Variabilidad de recursos, hábitat, y movimientos estracionales en aves Neotropicales: Implicaciones para la evolución de la migración a larga distancia. Bird Conservation International 4:109-115.
Levey, D. J. 1994. Why we should adopt a broader view of Neotropical migrants. Auk 111:233-236.
This opinion piece explains how and why research on migratory birds can benefit from a perspective that embraces the entire spectrum of seasonal movements. It provides predictions that can be tested in any migratory system.
Chesser, R. T. and D. J. Levey. 1998. Diet, habitat, and migration revisited: Austral migrants and the evolution of migration in New World birds. American Naturalist 152:311-319.
This paper starts with the theory proposed by Levey and Stiles (XX) and tests it on the austral migratory system. The predicted link between frugivory and the evolution of long-distance migration is not supported, but the link between seasonal habitats and migration is.
Pearson, S. F., D. J. Levey, C. H. Greenberg, and C. Martínez del Rio. 2003. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird. Oecologia 135:516-523
This paper provides an example of a technique widely used to study migratory birds in North America. In particular, it shows how stable isotopes can be used to discern bird diets. It is based on an experimental study in which a migrant species (Yellow-rumped warbler) was fed different diets (fruit-based vs. insect-based) in captivity. We looked for differences in stable isotopes of carbon and nitrogen in feathers and plasma.
Levey, D.J. 2004 (in press). Overview: Adaptations to two worlds. In: R. Greenberg and P. Marra (eds). Birds of Two Worlds. Smithsonian Institution Press. Washington, DC.
This is an overview of a section in a book that resulted from the “Birds of Two Worlds” symposium. Its theme is that migratory birds live in two “worlds” and that understanding one of those worlds requires understanding the other world.