You may already know about shade-grown, bird-friendly coffee, but do you know about the requirements for certification? One requirement is to have a high diversity and abundance of native tree canopies. Trees provide birds with shelter from weather and predators but the most important resource they provide is food! Food is the reason many of our migratory birds leave the states in the first place—there's much more food, specifically insects, in the tropical 'winter' than in snowy, cold North America.
There are lots of different herbivorous insects out there, but more than 90% of them are highly specialized to feed on only one kind of tree's chemical compounds. In addition, some species of trees are very productive insect producers, while others may not have any insects at all. For example, there are far fewer insects feeding on the tulip trees (Liriodendron tulipifera) than on the oaks (Quercus spp.) in your neighborhood. The same is true for trees on coffee farms. Because many migratory birds are highly insectivorous, some canopy trees may better support migratory bird populations than others. So far, however, no one has looked at bird-insect differences between individual species of trees on coffee farms, which is why I set out to visit some bird-friendly coffee farms this January.
During our recent trip to Nicaragua, Kerry Snyder (an undergraduate from University of Delaware), Dr. Robert Rice (from the Smithsonian Migragory Bird Center), and myself collected some preliminary data on which trees birds were foraging on, what foods they were feeding on, and what kinds of insects were available on trees. We were also looking at the variation of canopy trees on different farms to find suitable areas to collect data next year.
Seven different farms were visited in the districts of Carazo, Matagalpa and Madriz. We hiked through steep coffee farms looking for migrant birds and recording what trees they foraged in to compare to what trees were available to use. Many different warblers were found, including: black-throated green, black-and-white, Wilson's, chestnut-sided and even the threatened golden-winged warbler in bird-friendly coffee farms.
Some species like the Tennessee warbler occasionally foraged in fruit or nectar, but most were gleaning insects from leaves and twigs. One farm had a flock of over 50 different individual warblers foraging on only a few species of trees. Many of these birds were even found foraging directly on coffee plants, supporting that attracting birds to your farm can help pest control on coffee as well.
We spoke with several local farmers to learn more about which canopy trees were retained from the forest, and which were planted for shade or alternative crops. Kerry is staying for three more weeks and will be conducting more bird foraging observations as well as interviewing farmers to see why they chose to plant particular canopy trees over others. Hopefully, this new project will help strengthen recommendations for coffee canopy trees that benefit both the birds and the farmers, too.