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Birds, Bugs, and Agriculture: Is It a Sin to Kill a Mockingbird?

mockingbird

Some birds eat pest insects, and some eat crops, and some might eat both. Here, a juvenile Northern Mockingbird shows a thickened layer of strawberry fruit coating its bill, revealing at least one of its preferences. DNA analysis of the bird’s feces, however, can indicate if it also feeds on pest insects. (Photo by David Gonthier, Ph.D.)

By Karina Garcia, Elissa Olimpi, Ph.D., Daniel Karp, Ph.D., and David Gonthier, Ph.D.

“Mockingbirds don’t do one thing except make music for us to enjoy. They don’t eat up people’s gardens, don’t nest in corn cribs, they don’t do one thing but sing their hearts out for us. That’s why it’s a sin to kill a mockingbird.”— Harper Lee, To Kill a Mockingbird (1960)

With no disrespect to Harper Lee and her classic novel (it’s one of our favorites), it is actually quite challenging to understand whether a bird is entirely beneficial or harmful to crop production. For example, we have regularly trapped mockingbirds on strawberry farms in California with thickened crusts of condensed strawberry around their bills (think fruit roll-up consistency). But, on the other hand, using molecular diet analysis, our collaborators have found the DNA of Lygus bugs in mockingbird feces, indicating that mockingbirds eat the most important pest of strawberries in the region. So, is it a sin to kill a mockingbird? Do mockingbirds provide benefits to farmers more than they harm crops? If so, to what extent?

Karina Garcia

Karina Garcia, lead author on new article in Journal of Integrated Pest Management

Mockingbirds and their complex interactions with farmers are a great metaphor for birds in agriculture in general. There has been a long history of scientists trying to describe the role of birds in agriculture. For example, from the late 19th century and into the 1930’s, hundreds of studies were published under the field of economic ornithology, a discipline that largely depicted birds as benevolent benefactors of insect pest suppression. But, following the era of economic ornithology, birds were generally viewed as pests in agricultural settings. Our new review published this week in the Journal of Integrated Pest Management describes the current state of research on birds in agriculture, discusses examples of studies in which birds have shown to benefit rather than harm certain crops, and explores factors that might influence the net impact of birds on crop production.

For several decades, researchers have used bird exclusion to describe the net effects of birds on crops. Bird exclusion experiments typically prevent bird access to crops with coarse mesh nets that exclude birds but allow arthropods to pass through. Assessing the amount of insect pest damage in the bird exclosure treatment against the amount of pest and bird damage in a control treatment (in which birds are able to access the crop) allows researchers to describe the impacts of bird communities as neutral, positive, or negative.

However, describing the net effects of birds is just one piece of the puzzle. In order for farmers to be able to develop farm management strategies that either promote beneficial birds or deter harmful birds, it is essential to know which bird species are delivering services and which are delivering disservices. The use of DNA-based molecular analysis of bird fecal samples is key to determining the diet of wild bird species in specific farming contexts, revealing which bird species are beneficial and which are harmful.

From economic ornithology to ecosystem services, the study of birds in agriculture has always been important. Recent net effects studies and the application of molecular methods to study bird diets offer great potential for developing actionable insights into how specific bird communities affect specific crops in specific regions. This context-specific information will be crucial for integrating birds into integrated pest management (IPM) strategies. To ensure optimal delivery of ecosystem services (e.g., pest suppression) in agroecosystems, scientists must closely engage with farmers, landowners, and other stakeholders. Through collaborative efforts, research can inform management recommendations that are tailored to individual agroecosystems. Fortunately, more and more studies are simultaneously quantifying shifts in bird impacts on crops across farming, landscape, and regional contexts, offering the real possibility that birds may be incorporated in regional IPM programs in the near future.

Perhaps Harper Lee was on to something when she decreed it a sin to kill mockingbirds. Perhaps she knew that the benefits of some birds outweigh any harm.

Karina Garcia is a graduate research assistant in the Department of Entomology at the University of Kentucky. Email: karina_garcia@uky.edu. Elissa Olimpi, Ph.D., is a postdoctoral researcher in the Department of Wildlife, Fish, and Conservation Biology at the University of California, Davis. Email: eolimpi@ucdavis.edu. Daniel Karp, Ph.D., is an assistant professor in the Department of Fish, Wildlife, and Conservation Biology at the University of California, Davis. Email: dkarp@ucdavis.edu. David Gonthier, Ph.D., is an assistant professor in the Department of Entomology at the University of Kentucky. Email: gonthier.david@uky.edu.

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