by Jessica Bern
Be kind to your fine feathered friends – they may actually be of assistance on your farm. Joanne Baumgartner, the executive director of Wild Farm Alliance for over 20 years, led the first part of the discussion in “How Many and What Kind of Pests Do Birds Eat,” part of the “Role of Birds on the Farm” series. She began with a focus on Julie Jedlicks, Ph.D., who spent 10 years studying Western bluebirds in vineyards to see if they played an important role in pest control.
In one study, Jedlicks put nest boxes out in vineyards in Napa County, CA, with the control areas containing none. This resulted in a 10 times greater abundance of bluebirds present with nest boxes compared to those without them.
Jedlicks, using experimental prey (caterpillars) in the vineyard, found there were almost two and a half times more caterpillars eaten when boxes were present, and, surprisingly, three and half times more were eaten in areas immediately below the boxes.
In addition, after analyzing over 200 samples of the bluebirds’ feces, she found that half contained mostly herbivorous insects such as leafhoppers, but she was again surprised to find nearly 50% of the feces samples contained mosquitos compared to only 3% of beneficial arthropods, like spiders.
Another study, presented by Dr. Sasha Heath, an advisor on avian pest control, was set up to find out, based on habitat, would birds eat the codling moths she put out into orchards, as they are a huge pest for walnuts. The set up was 10 habitat orchards where they had riparian habitat or hedgerows near, or adjacent, to them versus 10 orchards with a clean margin.
Heath also looked at what kind of semi-natural habitat was in the surrounding area up to 500 meters away from the orchards. What she found were 10 types of insectivorous birds present in the margins that ate insects off the tree barks.
In the interior of the orchard, they found mainly two species of woodpecker – the Nuttall’s and the Northern Flicker. This is because more predators were present when there were margins with habitat than in those that were clean. Three factors that influenced the number of woodpeckers were the increased size of the semi-natural habitat, the presence of taller and older trees and when there were more fissures or cracks in the bark (where the codling moth likes to hide). As it turns out, the more complex the landscape, the less likely there will be predation by the woodpecker. In a complex habitat, there are more food sources for the woodpecker to choose from. It should be noted that the habitat also influenced the rate of predation in the interior of the orchard. Different types of birds live in different parts of a tree as well. Each builds a different nest, so even if the bird isn’t present, you can often figure out what kind built which nest.
Another study was done by Dr. Ellisa M. Olimpi on 30 organic lettuce farms along the central coast of California. She noticed that when it came to ungrazed habitat, such as trees and shrubs in riparian areas and wetlands, as well as surrounding grazed habitats, the study showed “…the more diversified farms supported different species of bird. However, there wasn’t much of a change in the conservation value of those bird communities. Here, conservation value incorporated population size, distribution and other components of variability, so a non-native species like a European starling would have low conservation value, but the conservation value of a native species, like an oak titmouse, would be higher.”
In the landscape surrounding ungrazed habitat, there was an increase in species richness and birds that were of higher conservation value because they tend not to form in flocks. This is helpful because the greater the size of a flock, the higher the risk of damage to crops. These types of birds are also not associated with livestock, decreasing the chance of contamination through their feces. Contrast this with surrounding grazed area, which tends to attract flocks of birds. The result is contaminated feces that could pass on foodborne pathogens like Salmonella, E. coli and Campylobacter. Interestingly, it was found that insectivorous birds, specifically, are less likely to carry Campylobacter as are birds not associated with livestock. Notably, promoting birds with nest boxes will provide pest control without compromising food safety. However, keep in mind that birds can eat some beneficial insects or consume crops directly.
Along the coast of California another study was done which involved 21 different organic strawberry farms and the impact of birds on over 10,000 berries. The economic impact of birds on the strawberry systems had to do with both the surrounding semi-natural habitat as well as the position of the strawberry crop in a field.
In a simple landscape, where the farm didn’t have much conserved habitat around it, birds caused some damage to the crops at the edges of the field, but in the center, they provided pest control. In a landscape that had more conserved habitat, the damage in the center wasn’t as noticeable but neither were the benefits – the conclusion being that one way to think about how the surrounding landscape can impact pest control is to think about adding or removing habitat.