Owls, Swallows and Bluebirds: The Secret Allies of Farmers

Dennis Tamura never set out to be a bird-watcher.

He’s been a farmer for over 35 years, and he and his wife grow organic vegetables and flowers on Blue Heron Farms outside Watsonville. But birds have become a part of the farm’s ecosystem.

About 15 years ago, a bird-loving neighbor put up small wooden bird boxes on the fence posts that line Blue Heron Farms, and Tamura just started noticing the tree swallows and Western bluebirds that came to visit. Today, he points out a fluffy baby tree swallow, its comically large yellow mouth peeking out of a hole in the box.

“The parents come by and you’ll see that their mouth is always wide open. ‘Hey, come on! I’m hungry!’ ” he said with a laugh. “It’s always kind of fun to watch.”

“Their habit is to just fly and dart around pretty low because they’re snagging insects on the fly. And then they swoop in and feed — boom — immediately, and then they turn around and go back out,” he said.

Just like he described, a handsome tree swallow, with its white belly and iridescent blue back, flew low over the crops, then turned toward a bird box.

“They feed them instantaneously. It’s pretty interesting,” he said.

Without landing, the parent put an insect in the baby’s mouth.

One insect Tamura worries about is the flea beetle, which loves eating plants from the Brassica family, like broccoli and bok choy. Some of the damage caused by the flea beetles is just cosmetic, he said. “But sometimes they can outright kill plants.”

Right around this time of year, when the birds begin to leave, he said, “I notice that there’s a lot more flea beetle damage.”

So the birds help with pest insects, and they’re getting something back from the farm.

Important Allies

Those bird boxes are simple, but they’re important. Pesticide use and habitat loss shrunk the bird population in North America by almost 3 billion since 1970. That’s nearly a 30% drop. The whole ecosystem feels that loss, since birds pollinate plants, and, like on this farm, control pest insects.

Birds like tree swallows and Western bluebirds would naturally build nests in tree cavities, but the plywood boxes all over the farm are a good substitute.

They also work well for barn owls. In his barn, Tamura pointed out the one box where barn owls have nested the last eight years or so, and help control his top rodent problem.

“There are a lot of gophers. I mean, we trap them but there’s no way we’re going to get them all,” Tamura said.

White droppings and clumps of regurgitated gopher cover the barn floor. Owls eat their prey whole and cough up the fur and bones, which they can’t digest.

Taking a look at the mess left behind by the birds, Tamura said, “Well, they eat a lot of gophers. It’s pretty astounding.”

Jo Ann Baumgartner runs Wild Farm Alliance, a nonprofit that helps farmers support, and benefit from, wild nature. The organization has developed a Songbird Farm Trail to map locations with bird boxes, monitor changes in bird population and encourage more participation.

“We want to see a million bird boxes,” she said. She added little metal tags to the bird boxes on Blue Heron Farm, and will observe bird behavior here. Monitoring bird life in boxes will add to the growing citizen science and academic research about beneficial birds.

These studies used to be common, Baumgartner said. “Back in the 1880s, the precursor to the USDA started studying how important birds were for eating pest insects and rodents. They asked farmers to shoot birds, which you could never do today, and pickle their stomachs and mail them in.”

These researchers studied the birds’ stomach contents, she explains, which led to a flurry of research papers published afterward on this topic.

When pesticides gained wide use, Baumgartner said, these studies fell by the wayside. But, over the last two decades, researchers have started to study once again the benefits birds provide to farms.

Matt Johnson, professor at Humboldt State University, spends his days studying the relationship between birds and farms.

He said that in Napa County, where he conducts his research, “the Wappo were the indigenous people here. They managed this place with a lot of traditional fire, keeping it an open grassland, with huge oaks that the first European colonizers waxed poetic about.”

But he added, “a lot of that habitat is gone and has been replaced by vineyards.”

Johnson drove through a vineyard in American Canyon, stopping to check owl boxes for nests or eggs. He got out of his truck and walked towards an owl box about 15 feet off the ground and pointed out the scratches on the outside of the hole, a good sign that there’d been recent activity.

Quietly approaching the box, he extended a painter’s pole with a GoPro camera attached to the top, which connects to his phone. Slipping the GoPro into the box, Johnson looked at his phone to get a view of what’s inside.

“Male and female,” he whispered. “I can see an egg underneath the female. I’m going to get out of there.”

People have built birdhouses for centuries, and Johnson says that farmers from Chile to South Africa put up barn owl boxes because they’ve seen barn owls eat rodents on their farms.

“They don’t necessarily need a lot of scientific evidence to show that this is working. They’re seeing it on the ground,” he said. The academic research on the impact of owls on farms, however, was slim, so Johnson began the Barn Owl Research Project in 2015.

“Now we have some scientific evidence,” he said.

Johnson’s team installed infrared cameras in owl boxes all over Napa Valley to monitor what owls hunted at night, and placed GPS trackers on owls to see where they hunted.

“Our estimate is that a family of barn owls removes 3,400 rodents from the landscape every year,” Johnson said. “So some of these farms, like this one that has 20 occupied boxes, you’re talking about 70,000 rodents removed every year.”

Their research showed that one-third of these rodents came directly from vineyards.

This vineyard was started by the man who helped put California wines on the map.

In the mid-’70s, Miljenko “Mike” Grgich was the winemaker for Chateau Montelena, the vineyard that beat French wine in a taste test that became known as the Judgement of Paris. He went on to start Grgich Hills Estate, where his nephew, Ivo Jeramaz, continues the winemaking tradition.

While Johnson checked the barn owl boxes, Jeramaz walked by and said he’d love to add more to his vineyards. Johnson explained that after analyzing this season’s data, his team can point out new locations that owls would probably like.

‘Conservation With People’

A few weeks later, Johnson met up with three grad students at another Napa vineyard to collect data and place ID bands on barn owls to study them for years to come.

They walked down to a box, wearing headlamps. First, they checked the owl box. Next, they set a trap for an adult returning to feed its young. The box is designed, Johnson explained, so that when an owl enters it, a little door swings shut and LED lights turn on.

After a short wait, they all see movement. “So an adult owl flew in,” said Johnson. “We think it might be the female. She landed on the box and she’s … .”

Before he finished his sentence, the light turned on. “Oh, there she is. She’s inside! Let’s go!”

The team quickly walked down to the box, set up a ladder and listened in to the parent feeding baby owls.

Making sure the adult didn’t escape from the side door, Johnson asked one of the graduate students to shine a light inside the box while he reached in with a gloved hand to grab the owl’s feet and pull it from the box.

The owl appeared, with its white wings spread wide out from its heart-shaped face. They put a little hood over its head to calm it down.

When they got back to the truck, graduate student Laura Echávez said that the next step is to take a metal band issued by the U.S. Geological Survey and place it around the foot of the owl.

She held the owl with confidence and tenderness, talking to it softly as she secured the metal band. “Can you lift your head a little buddy?” she said. “There, perfect.”

Then, after about 20 minutes of taking measurements and photos for their research, the team returned the owl to the box.

Johnson hopes his team’s research can highlight the reciprocal relationship between farmers and wildlife.

Barn owls are one species that depend on oak trees, using the big cavities around the tree’s trunk to build nests. But with the growth of the vineyards and other development, many oak trees in this valley have disappeared.

“When farmers put up these nesting boxes, it’s amazing,” Johnson said.

“There’s an old conservation model where the idea is that we need to protect nature from people, and just lock it away and keep people out,” he explained. The flip side would be conserving nature exclusively for people.

“Neither of those is really quite right. I think we should think about conservation with people, you know, understanding that we are part of the ecosystem and we do things that negatively affect some species,” Johnson said. “We can also do some things that help species survive and they in return can help us.”

‘They’re Welcome to Be Here’

Back at Blue Heron Farms outside Watsonville, farmer Dennis Tamura says that having the barn owls, tree swallows and Western bluebirds nest in boxes on his farm has done more than just offer pest control — they help him see his farm more deeply.

“Seeing what you’re looking at, it’s different than just looking and watching,” he said.

“They’re welcome to be here because there’s plenty of food, as far as I can tell. For me, they just enhance the whole environment. And obviously they do some help for us.”

And, I pointed out, he provides a home for them.

“Yeah,” he said with a laugh, “I guess you could say that.”

That seems like a pretty fair trade.

This piece was produced in collaboration with the Food & Environment Reporting Network, a nonprofit, investigative news organization. The author produced the story while in residence at The Studios of Key West.