If you enjoy sitting on a deck, porch or patio and being serenaded by songbirds as you sip your morning coffee, the experience is in danger of becoming less enjoyable.
Various studies and surveys have shown that North America's neotropical migrant songbirds are in decline partly because their winter grounds are being converted from forest to agriculture. Now, a first-of-its kind study is focusing on the relationship between migrant birds and the insects attracted to trees that provide the canopy for shade coffee grown in Central and South America.
The research is being conducted by two scientists, one of whom is known for his work with birds, Robert A. Rice, and one who is known for his research into the evolutionary relationship of insects and trees, Doug Tallamy. Rice is a research geographer with the Smithsonian Migratory Bird Center and has spent considerable time promoting bird-friendly coffee-growing practices in Central and South America. Tallamy is a professor of Entomology and Wildlife Ecology at the University of Delaware who recently discovered that there are big differences among trees in how well they sustain birds.
Rice and Tallamy are concerned that the increasing demand for coffee is having a disturbing effect on neotropical migrants. Songbird species that spend seven months of the year foraging for insects in mid-elevations of the Neotropics (Central and South America) are particularly vulnerable because these are the areas that are best for coffee production. Breeding-bird surveys have found populations of many of these migrants are declining at rates of 3 percent or more per year. The problem, Tallamy said, is two-fold: Some shade coffee farmers have cleared out native understory trees and replaced them with non-native trees while other landowners have converted cow pastures to shade coffee farms and planted non-native canopy trees.
"Farmers have chosen replacement trees based on traits such as fast growth and their ability to be used for dual purposes such as lumber or the production of citrus and mangos," Tallamy said. The problem with this, he said, is that unlike native trees, the non-natives support few if any of the insects that provide the food the overwintering migrants require.
Non-native trees that have gained popularity on the shade coffee farms include trees from Australia such as Eucalyptus, Casuarina and Grevillea. Yet bird conservation organizations promote shade coffee as an ecologically green way to grow coffee.
"This assumes that all canopy trees are equally good at supporting birds as long as they create shade," said Tallamy. "But this is not true," he added. Tallamy said his research data clearly show that non-natives, whether in Central and South America or in North America, support fewer insects than native trees and shrubs.
A coffee farm in Colombia in 2008. (Photo: Brian Smith/American Bird Conservancy/U.S. Fish and Wildlife Service Northeast Region/flickr)
Tallamy and Rice are concerned that there has been a decrease in insects in elevations of the shade coffee farms that is leading to a decrease in bird populations in these areas, both migrants such as warblers as well as year-round resident birds. However, insect populations in these regions haven't been fully measured yet, so Tallamy said it is too early to draw a definitive conclusion. "This is one of the things we would like to accomplish with our research," Tallamy said.
Among the migrants that have been affected are golden-winged, Canada and cerulean warblers. "The cerulean warbler is a poster child of bird declines," Tallamy said, noting its population has been decreasing by as much as five percent a year.
The yellow warbler is another bird that Tallamy and Rice are monitoring. Tallamy described it as a very visible species that indicates which trees are attracting insects. "Where it goes, other insect eaters go," he said. "It is a common insectivore so even when the other birds are too rare to measure, we can see what yellow warblers do and know they are telling us which trees provide the best food for other warblers," Tallamy explained.
Several endangered neotropical resident birds have also been severely impacted by coffee production, according to the website of the Cerulean Warbler Bird Reserve, which is located near the small town of San Vicente de Chucuri, southwest of Bucaramanga in central Colombia. These include mountain grackle, chestnut-bellied hummingbird, white-mantled barbet and the turquoise dacnis.
The problem is compounded when the migrants fly to the United States, moving across the North American landscape to historical breeding grounds. Urban sprawl and commercial development, which more often than not favor planting of non-native trees and shrubs, have replaced many natural U.S. habitats. Data from Tallamy's studies in the United States have convincingly demonstrated that tree species differ widely — sometimes by orders of magnitude — in their ability to serve as hosts for the insects birds eat and that native tree species are significantly more productive in supporting bird food webs than non-native tree species.
"We're starving them on both ends," Tallamy said of the warblers and other neotropical migrants. He cited the cerulean warbler, which breeds in the central United States from Kansas to Southern Michigan to Eastern Pennsylvania as being particularly affected by habitat loss, especially due to mountaintop tree removal in West Virginia.
The cerulean warbler is just one of my birds facing threats from improper shade coffee tree planting in South American countries and urban sprawl in the United States. (Photo: WarblerLady/flickr)
He and Rice are hoping their studies in Central and South America will help reduce this problem in the birds’ winter grounds by determining which tree species best serve as hosts for the insects that wintering migrants need. Tree species used in shade coffee are regionally specific, and until Rice and Tallamy began their studies no one had compiled scientific information about which tree species are best for bird conservation throughout the coffee growing regions of Central and South America.
As shade coffee growers remove existing trees in favor of mixed-use trees or as land owners plant mixed-use trees when converting cow pastures to shade coffee, it's important to use the most ecologically productive tree species. "It's not that all canopy trees used in shade coffee are bad," Tallamy said. "It's more that we haven't looked for the ones that are best and because of that we haven't promoted the good ones," he explained.
To establish that information and help environmentally conscious growers decide which insect-productive shade trees to plant on their farms, Disney awarded a one-year Disney Conservation Grant to Tallamy and Rice in October 2014 to fund their research. Their study has three primary goals:
1. Establish common garden experiments in Nicaragua to compare various shade tree options in terms of their ability to produce the insects birds eat while wintering.
2. Quantify bird foraging success on different tree species within shade coffee farms.
3. Compile literature host records of caterpillar species to rank tree candidates for shade coffee in terms of their ability to support insect herbivores.
That grant will expire in September, but on March 6, Tallamy and Rice applied for a second year of funding. If approved, they would use the new funding to compare the conservation value of shade species in different neotropical coffee growing regions. They would do that by continuing to monitor insect production in a Nicaraguan test garden, establish new common gardens within or near Cerulean Warbler Bird Reserve in Colombia and communicate their findings to coffee growers throughout the neotropical coffee growing areas at formal symposia, on a dedicated website, and in newsletter publications.
How will Tallamy and Rice know if their efforts are making a difference? One way would be to improve the criteria for shade coffee farms and the coffee they produce to be labeled bird-friendly. "It's that important to me," Tallamy said.
A sun coffee farm in Nicaragua. Such coffee farming doesn't rely on shade from trees, depriving birds of habitats. (Photo: Dennis Tang/flickr)
Another measure of success would be to give the ever-increasing number of growers who plant sun coffee, which produces more beans than shade coffee and requires no shade from trees, information that would enable them to convert their sun coffee to shade coffee using canopy trees that are the very best for the birds. "I would love that!" Tallamy said.
A bonus would be if developing areas in the tropics adopted the bird-friendly tree approaches Rice and Tallamy are studying. "There is no reason why people in cities and suburbs can't use the high-value trees we discover as well," Tallamy said. "It would make the entire human-dominated landscape more bird friendly."
That, after all, is a goal of his work with U.S. native plants. Continuing to hear songbirds as you have your morning coffee just might give you a clue as to how well the message is being received throughout the Americas.