Putting Birds to Work

Even dedicated birdwatchers rarely think of birds as essential economic actors. In many instances, however, this is exactly what they are. In addition to pollination services, waste disposal, and disease control, some of those pretty birds are among the many creatures that undertake economically vital jobs as pest controllers.

Dutch scientists Christel Mols and Marcel Visser measured the level of damage to apples in an orchard where great tits were nesting, compared to orchards where they weren’t. [The great tit feeds on insects and spiders. It is common to Europe, the Middle East, Central and Northern Asia, and parts of North Africa.] To increase the number of nesting great tits in some of the study areas, they put up nest boxes.

The results demonstrated a striking effect. In the areas where the nest boxes were used, the number of apples damaged by caterpillars was reduced by half. The areas with the most great tits also had the best harvest of high-quality apples.

The authors concluded that reducing caterpillar damage in orchards by offering nest boxes to great tits is an extremely low-cost measure that can increase the harvest of undamaged apples by more than a ton per hectare per year. Less pesticide is needed, and that is of benefit to the fruit grower (in cutting costs) and of course beneficial for other wildlife (in not being poisoned).

Fruit and vegetables are not the only beneficiaries of pest control duties carried out by birds. The supply of one of our favorite beverages is also in part due to birds. Work carried out in the Blue Mountain highlands of Jamaica shed some light on how much. Matthew Johnson of Humboldt State University in Arcata, California, along with two of his colleagues, examined the effect of birds in cutting down insect damage in a shaded coffee plantation.

Coffee was once routinely grown under tall forest trees. Recently it has more often been grown in full sun so as to boost productivity. While additional sunshine can boost short-term yields, shade can, among other things, provide cover and nest sites for birds. The birds need to eat, and what they eat includes the insects that would otherwise damage the coffee crop. In this case the birds were found to have a major impact on the population of an insect called the coffee berry borer—the most damaging coffee insect pest in the world. When the effect of the birds was assessed on the coffee yield (by experimentally excluding them from certain areas with nets), they were found to be providing about $310 worth of value per hectare.

High in the hills of Kenya and Tanzania, Unilever owns extensive tea estates. Among the remarkable characteristics of these places is the fact that they don’t use any pesticides. One possible reason why they have been able to get away with this is the areas of natural forest and other habitats that have been protected and nurtured since the plantations were set up in the 1920s. The forests also keep the atmosphere moister and provide wood for drying the tea leaves.

Richard Fairburn works for Unilever.He has spent many years in East Africa and knows the tea business there very well. He says the trees have been retained on the estates for good practical reasons, to conserve soil and to help stop fertilizers from getting into the rivers. On both these counts the protection of the forests has been a very successful strategy. The trees also help ensure that rivers continue to flow in drought periods and act as corridors that allow wildlife to move freely around the estates, including many kinds of birds. And this in turn might be why there have been so few problems with pest infestations. “When I went to our Kenyan estate in 2001,” Fairburn says, “there was an old planter’s wife who thought there were 100 species of birds there. I didn’t know if that was right and so decided to get the National Museums of Kenya to do a proper survey. They found 174 and said that if they had more time the true figure might be more like 220.”

Given the progressive development of resistance to pesticides by a range of harmful pests, these and other findings are of far more than passing interest. Birds and other predators can evolve in step with their insect prey. Where our chemicals can’t easily keep up, the birds can and do. This is a point that is not, of course, only relevant to tea.

Mols and Visser, reflecting on their findings in the Dutch orchard, remarked how they felt the role of birds in pest control had generally been overlooked. They didn’t speculate as to why this might be, but in technologically obsessed societies might it be that we more easily relate to a person with an insect spray than we can a small bird going about its daily business? Have we become blinded to the obvious? Or is it that there is more money to be made from selling pesticides than nest boxes? Or perhaps we have approached economics wrongly, in for example being able to put a financial value on the chemicals, but not that of the birds? I suspect it is a combination of all three.

Whatever the reasons, the more we look, the more we discover how a host of services provided by different animals has a huge economic value in pest and disease control. And it’s not only in relation to food production that it has been possible to put credible economic estimates on the value of the work.