Songbird nesting sites have decreased due to disruption of woodland and savannah habitat. Creating nesting boxes for songbirds in vineyards provides habitat for native birds, such as the Western Bluebird, as well as providing a biocontrol for insect pests on vineyards. Western Bluebird abundance increased by a factor of nine in nest box treatments throughout the breeding season. Additionally, there was a significant decrease in larvae both immediately adjacent to occupied nest boxes (average 83% larvae removal) and at randomly selected points (average 58% larvae removal) throughout the nest box treatments of the vineyard. Overall, conservation looks like a win-win scenario for wine grape growers.
Julie Jedlicka and David Koball share post-project perspectives
Project investigator Julie Jedlicka hand-built the 200 or so nest boxes that were installed at Fetzer Vineyards for this project. She said what was most gratifying was the response of the birds once the boxes were set in place.
“I guess what I was most overwhelmed and excited about was the response the birds had to putting up the boxes,” Jedlicka says. “It felt good to be able to provide the grower with this resource.”
Overall, 54% occupancy rates were achieved in the 2008 breeding season which began only four months after the nest boxes were placed in the vineyards. As a "thank you" to Fetzer Vineyards for their cooperation in this project, Jedlicka has donated the boxes for their continued use in the vineyard.
Jedlicka continues to investigate ways to evaluate the birds’ pest management effect in the field, in particular using new methods to evaluate bird fecal samples to identify what birds are eating. Jedlicka is working with a lab at UC-Berkeley to molecularly identify insect remains in bird fecal samples through DNA extraction. This method more accurately identifies which insects birds have eaten than is possible solely through a visual identification. Jedlicka notes that visual identification of fecal samples is biased by what the researcher can actually see, which can be limited and vary among insect species. “This is a really new field. I’ve looked through the literature and very few biological studies are using this extraction method,” says Jedlicka, who also says she hopes to continue DNA extraction work in her post doctoral studies.
David Koball of Fetzer Vineyards, who worked closely with Jedlicka on the study, says he’s glad to have the nest boxes in the vineyard. “From my standpoint, there are more birds in the field,” which he says is rewarding from a conservation perspective.
However, leafhopper pressure has been high this year, and the presence of birds has not replaced the need for use of organic materials to help manage the insect pressure. Koball says he hopes that further systems research will help vineyard producers implement multiple biocontrol strategies for pest management.
“What I’d like to see is someone put it all together, so we can look at using nest boxes and cover crops and other insect habitat and be able to say something like: ‘With this density of birds, this density of minute pirate bugs and this density of green lacewings, etc., we can expect x-amount of leafhopper control in a normal year.’ Because we know it’s not about depending on one element to provide all the control we need,” says Koball.
Koball says that outside of a research project he would definitely continue to use nest boxes in organic vineyard management but is not sure he would have them at the density or in the arrangement implemented in this study, noting that they can get in the way of machinery in the field. He noted that locating nest boxes on field perimeters might be a preferred arrangement. --Erica Walz
Complete Project Review: /sites/ofrf.org/files/staff/jedlicka_08f36.pdf
Project Summary: /sites/ofrf.org/files/staff/jedlicka_08f36_summary.pdf
PLoS One, November 9th, 2011: http://www.plosone.org/article/info%3Adoi/10.1371/journal.pone.0027347