Scientific interest in neotropical migratory birds blossomed in 1977 in Virginia. A symposium sponsored by the Smithsonian Institution marked the realization that most species evolved in the tropics and use temperate forests as a reproductive strategy: a watershed in the approach to research and management of neotropical migratory birds.
Now, over thirty years later, an in depth review requested by the Ecological Society of America reports on the extent of our knowledge on neotropical migratory birds in 2010. The report was led by John Faaborg and Richard Holmes and and co-authored by 18 others and appears in the journal Ecological Applications.
Exhaustive in its scope, the paper neatly breaks down migratory bird ecology into breeding, autumn migration, wintering and spring migration.
Not surprisingly, the two migratory periods have the greatest lack of knowledge. But there are significant gaps to be found everywhere: “In many cases, the decision about where population limitation occurs for a species is just an educated guess.”
For each season, the paper outlines both conservation strategies and research priorities.
Those looking for a shopping list of priorities will be disappointed. The approach is more contemplative. Specific recommendations deal with the larger picture and political and fiscal realities of working in North America.
They note few individual species have sufficient natural history knowledge. This is likely due in part to the sheer number of species in question.
But the science of ecology also has to take partial blame for its movement away from basic natural history toward a more reductionist approach of hypothesis testing. The latter is surely needed, but is ultimately reliant on a sound foundation of species’ natural history.
The paper also examines ecosystem-level constraints on migratory birds, touches on potential the role of climate change and takes a close look at the chief agency set up to manage migratory birds in the U.S. and Canada: Partners in Flight.
The ultimate question is what limits migratory birds. As expected, the answers are as diverse and complex as the species themselves.
Ovenbirds (Seiurus aurocapilla) are often cited in the paper as an example of the challenges facing ornithologists and mangers. Throughout the U.S. Midwest, the species strongly avoids edge. Move north to central Canada, and the same species readily occur in much smaller habitat fragments.
How do managers resolve such conflicting results? The answer isn’t always apparent. Meanwhile, on their wintering grounds in Puerto Rico, ovenbirds have declined to <20% of 1973 abundance.
So do we know enough about migratory birds? The authors strongly conclude “almost certainly no” but suggest there is more than enough knowledge for conservation efforts to proceed apace.
Funding of course is critical. The topic arises several times in the paper with both good news and bad. What the authors do not address is how to convince both public and private sources to prioritize neotropical migratory birds in a time of massive government deficits and private sector cutbacks.
As the researchers note, much has been learned in the 30 years since that groundbreaking conference in Virginia. Yet substantial gaps in knowledge remain and the challenges facing migratory birds today require even more work.
--Reviewed by Ian Adams
Faaborg, J., Holmes, R., Anders, A., Bildstein, K., Dugger, K., Gauthreaux, S., Heglund, P., Hobson, K., Jahn, A., Johnson, D., Latta, S., Levey, D., Marra, P., Merkord, C., Nol, E., Rothstein, S., Sherry, T., Sillett, T., Thompson, F., & Warnock, N. (2010). Conserving migratory land birds in the New World: Do we know enough? Ecological Applications, 20 (2), 398-418 DOI: 10.1890/09-0397.1