Wednesday, November 14, 2012

The Importance of Cycles

Font Hill Nature Park, Jamaica
Tuesday evening a group of Washington College community members, students, faculty, and staff had the opportunity to hear Dr. Peter Marra lecture on "Studying Birds in the Context of the Annual Cycle: Carry Over Effects and Seasonal Interactions." In his talk Dr. Marra explained the importance of looking at the entirety of a system instead of one of its parts. This might sound silly, but it's exactly what scientists have been doing for decades! Marra described the trend in the past few decades to focus research efforts on the breeding season and only sometimes study the wintering season or the spring and fall migration periods. Marra is arguing for a new approach to ornithological research, one that places importance of considering the entire cycle, which is an approach termed "migratory connectivity." Migratory connectivity basically means considering the wintering grounds and migration paths as well as the summer breeding grounds. There are many ways to quantify migratory connectivity, but here are a few:

 • bird banding
 • morphological variation (differences in wing, leg, bill length etc between populations)
 • molecular markers
 • stable isotopes (levels of certain elements in tissues indicate the latitude at which a bird molted its feathers)
 • light level geolocators (small chips that record the amount of light they are exposed to and allow for more precise calculation of lat. and long.)
 • satellite and cellular transmitters (frequent broadcast of location to towers and satellites)

 The implications for conservation as a result of this new paradigm are far-reaching. Marra's research into migratory connectivity has shown that it is not enough to preserve one area that a species relies on for some aspect of their life cycle. For instance, preserving the summer breeding habitat of a Grasshopper Sparrow will ensure that the birds that arrive to breed can do so, but it will not protect them when they leave for the next 8 months for their wintering territory. Many of the birds that are declining in the US are migrating songbirds that travel to South and Central America to over winter. We are doing a good job of protecting their summer habitat, but as long as the winter habitat remains unprotected the populations will continue to decline. This initial research and study has prompted Marra to undertake a "Migratory Connectivity Project." This project has the extremely ambitious goal of mapping the breeding, wintering, and migration territories for each North American species of bird so that we can more effectively protect their habitat.

American Redstart
Much of the research that has prompted Marra's understanding of the annual cycle and migratory connectivity was conducted with American Redstarts. These small warblers travel from the US to the Caribbean to overwinter and have been studied on their wintering habitat for over 20 years. From his study with the "Jamaican-American" Redstarts, Marra noticed that the quality of habitat on the wintering grounds was affecting the timing of migration and ultimately the success of individual birds on the breeding grounds. In fact, Marra notes that the number of young produced on the breeding grounds has more to do with the quality of the non-breeding habitat than the quality of the habitat on the breeding grounds! He was able to document this by contrasting the individual success of birds who had experienced a dry winter habitat vs those who had experienced a wet wintering habitat. The American Redstarts that had access to the more fertile wet habitat were able to produce more offspring than those who were relegated to the dry habitat.

Mangrove Swamp (wet habitat)

Forest (dry habitat)

Marra's work with American Redstarts has paved the way for what can truly be considered a paradigm shift in how we think about avian conservation. By recognizing the importance of the entire annual cycle Marra is providing challenging new ways to engage in habitat conservation and bringing new challenges to surface. More data is needed to develop something like a Migratory Connectivity Project, but each bird banded, radio tagged, or sampled for isotope analysis is a step toward a better understanding of our world and the many creatures that inhabit it.

American Redstart

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