Date: November 23, 2016
Source: Central
Ornithology Publication Office
Do bluebirds nesting in
California's vineyards help grape growers by eating agricultural pests, or hurt
them by eating insects that are beneficial? The researchers behind a new study
in The Auk: Ornithological Advances found that bluebirds' presence is likely a
net positive -- and they did it by analyzing DNA in bird poop.
Bluebirds are one of
several groups of birds that catch insects on the wing, but because they're
constantly on the move and the animals they eat are tiny, it's difficult to
determine exactly what species make up their diet. Julie Jedlicka of Missouri
Western State University and her colleagues tackled this question using a new
approach called "molecular scatology," analyzing DNA fragments in the
birds' feces to determine insect species the bluebirds were eating. They found
that Western Bluebirds in Napa Valley vineyards mostly ate mosquitos and
herbivorous insects, likely having only negligible effects on the predaceous
insects that benefit vineyard production by eating pests. Jedlicka hopes that
these results encourage more vineyard owners to install bluebird boxes, helping
replace natural tree cavities lost when land is cleared.
Jedlicka and her
colleagues collected 237 fecal samples from adult and nestling bluebirds living
on three vineyards in Napa County, California. "Many people I talk to get
a very romantic vision in their minds when they think about how beautiful it
must be to do fieldwork in California vineyards, especially in the Napa
Valley," says Jedlicka. "Honestly, the landscape was beautiful, but
the fieldwork is very demanding. Temperatures during the summer often rose into
the 90s and 100s, and I was lucky to have wonderful help from vineyard farm
workers and undergraduate field assistants."
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