** The following is the second in a series of blog posts by Wild Lens biologist Erin Strasser. Her work in Honduras will be depicted in a Webisode during the coming weeks. **
Fabiola, Brett, and I wait patiently amongst the coffee branches, hoping to catch a glimpse of cinnamon- brown, straining to identify sounds beyond the ear numbing chicharras, or cicadas. What we are so eager to find is the Wood Thrush (Hylocichla mustelina), one of our focal neotropical migrants and a species of special concern due to population declines over the past several decades. At first glance the Wood Thrush or zorzal del bosque may not be the most charismatic species. However with their bold black chest spots, blank stare, bobbing motions as they forage in the leaf litter, and their agitated and bursting “pit pit pit pit pit” call they quickly piqued my interest.
The Wood Thrush spends its breeding season in deciduous forests of eastern North America. As a neotropical migrant (NMB), that is, a bird that breeds in North America and migrates south to Latin America for the winter, the destruction and fragmentation of both breeding and wintering habitat are suspected factors in this species’ decline. Shade grown coffee fincas (farms) may act as a winter refuge, mimicking natural habitat by providing cover from predators and dense leaf litter necessary for foraging. However, depending upon the size or quality of certain habitats, or the number of Wood Thrush defending winter territories in an area, birds may be forced to move into more disturbed or less favorable sites potentially lowering their chances of survival.
A major aim of this project was to gather information on Wood Thrush overwintering habitat requirements in Honduran shade-grown coffee fincas and adjacent forest fragments. What factors influence overwintering survival, movement patterns, and prepare birds for the long migratory journey back to the breeding grounds?
To monitor thrushes we trapped birds, marked them with individually numbered federal aluminum bands and a unique color band combination, and more often than not, fitted them with a small (< 1.5 gram) VHF radio transmitter. These transmitters were designed so that if we were unable to recapture birds and retrieve them, they would fall off after several weeks. After approximately 6 weeks the transmitter’s battery dies. In the case of a few of our birds, there was enough time in the season to replace the transmitter and continue tracking for several weeks.
Although we captured most of our birds passively with strategically placed nets, we also used playback, a thrush decoy, and a concentrated net arrangement. During these episodes, we spent countless hours crouching under coffee, slipping down muddy hillsides, rushing birds towards the nets and dealing with misleading radio signals bouncing off of wet, shiny leaves and streams.
This season we were able to capture over two-dozen Wood Thrush, and place transmitters on about 20 individuals. One of our birds was aptly named “Boise” in reference to its Boise State University influenced orange and blue color bands. Birds such as “Boise” were tracked several times a week. Locations were pinpointed by visual observations and/or triangulation: the art of taking several GPS points and associated bearings quickly and from various angles. While “Boise” remained fairly loyal to its territory in a shady finca, other birds congregated at sites for only a few days before moving on, while others divided time between coffee fincas and adjacent forest.
Brett’s research will likely elucidate why and for how long certain birds utilize a particular area and whether this is related to age, sex, or body condition. At a larger scale, studies such as this will help biologists identify how to effectively integrate forest corridors, fragments, and shade to maintain or increase viable NMB habitat. In turn, this may increase the value of shade-grown coffee for local coffee cooperatives and their farmers while promoting fair-trade and sustainable coffee farming practices. If you are interested in supporting NMBs and fair-trade cooperatives, and purchasing shade grown coffee, visit Café Solar’s website. Also, visit Brett Bailey’s webpage for more info on his research.
Stay tuned for more on our research and adventures in Honduras. All I can say is we encountered a lot more than birds. – Erin Strasser