Shade Trees in Coffee as Smorgasbords for Birds: Which Trees Offer the Most Insects?

November 5, 2014 by Robert Rice


November in Nicaragua marks the end of the rainy season, a pretty good time to dig holes, plant some trees, and lay out an experiment in the Department of Carazo, just south of Managua. With funding from Disney's Worldwide Conservation Fund, SMBC staff, colleagues from the University of Delaware, and two coffee farmers here in Carazo have set up a field trial in an effort to figure out which shade tree species that coffee farmers use make the best buffet offerings for birds. Here's our thinking:

A beetle on one of the avocado seedlings

Many birds are insectivores, and most birds feed insects to their young. A host of insects inhabit vegetation, and coffee farms with a shade cover have a wide variety of tree species. But how many species of insects make their living on the different tree species in a coffee plantation?

We know from our own work and from that of others that any setting with lots of different trees that create a tall canopy with different layers of vegetation below results in pretty good habitat for many bird species. Coffee farms with a diverse shade tree community that meets these characteristics have been shown to offer viable, quality habitat for birds, some insect groups, and, most recently, small mammals.

The agroforestry setting (the coffee crop and the associated shade trees) mimics a forest in some ways, which provides the required conditions the wildlife needs. (It's not equivalent to natural forest, mind you, but for an agriculturally productive holding, it comes closer than any other we've seen to date in terms of bird diversity.)

What we don't know is which tree species attract and offer a living for the most insects—a primary food and protein source for many birds. Enter Doug Tallamy, our colleague from the University of Delaware. Dr. Tallamy is an entomologist who has devoted much of his career to looking at exactly this question: how many insect species make a living on specific tree species?

In the United States, he's found that oak trees supports upwards of 250 distinct insect species. Other trees, such as the Tulip Poplar, host a meager 19 insect species by contrast. So, different tree species support vastly different numbers of insect species.

Digging holes for the seedlings of 16 different tree species

So, in an attempt to tease out which shade tree species support the greatest insect diversity, we've set up a pilot project to find some answers. We've planted 16 species of shade tree seedlings. Some are forest species that provide varying degrees of shade, while others are fruit tree species like tangerine, avocado, or mango. All are common shade trees in coffee farms.

Mango seedlings in the ground

Now that they are in the ground, we will monitor them over the coming months to determine the insect populations on each species. Two farmers in Nicaragua's southern coffee region of Carazo—Jefferson Shriver and Keith Poe—have graciously and enthusiastically provided sites on their farms for the field trials. We appreciate and applaud their interest in and commitment to science. As the months progress, we'll see which tree species provide the better buffet for birds and other insect-eating wildlife.

What then? Well, then we can recommend to growers, who want to enhance the resources offered to birds, which shade tree species provide the largest smorgasbord. Yum-yum!