How many people have sat back and watched as their yards are swarmed by birds? Hummingbirds, bluejays, sparrows, doves, pigeons, and seagulls are common in the region.

And let’s not forget turkeys, hawks of various types and the occasional pheasant.

What you probably don’t think about is all those birds poop, and when it comes to bird poop, size can matter in spreading diseases. And I’m not talking about wiping bird poop off your car.

Rather, it’s a problem for farmers, according to a story prepared by UC Davis writer Kat Kerlin, “It doesn’t require a degree in ornithology, a lab test or even an app for most growers to determine whether bird poop near their crops presents a food safety risk. They just need to ask themselves a simple question: How big is it?”

Published in the Journal of Applied Ecology, the study looked at food-safety risks and wild birds as a way to “help growers avoid crop losses and manage farms for food safety, biodiversity conservation and crop production.” But it could also affect those of us who have fruit trees and gardens.

Kerlin reported since 2006, when an E. coli outbreak devastated the U.S. leafy greens industry, “growers have been pressured to remove natural habitat to keep wildlife — and the foodborne pathogens they sometimes carry — from visiting crops.

“Growers are often advised not to harvest crops within a roughly three-foot radius of any wildlife feces, lest they risk failing a food safety audit or losing a buyer contract,” Kerlin writes.

Personally, if I was ever operating a tomato harvester, I wouldn’t be looking for bird poop or any poop for that matter, but it’s a good question because we want our food to be free of disease.

“We wanted to find out the true risk of wild birds to food safety,” said lead author Austin Spence, a postdoctoral researcher in the UC Davis Department of Wildlife, Fish and Conservation Biology. “Which birds have pathogens, which birds are spending time on farms, and if a bird has a pathogen, does that pathogen survive long in bird poop?”

Now, if you thought this job was easy, Kerlin reported researchers looked at nearly 10,000 birds across 29 lettuce farms on California’s Central Coast. They spent hours collecting hundreds of bird poop samples.

They compared E. coli survival in bird droppings on lettuce leaves, soil and plastic mulch to measure pathogen persistence.

After all of this work, “they landed on a simple finding: Smaller poops from smaller birds carry very low risk of foodborne pathogens, which were rare in birds overall. If a bird were to become infected, pathogen survival depends heavily on the bird’s size,” Kerlin states.

“Birds that are large produce really big feces, and that’s where pathogens are more likely to survive,” said Spence. “Birds that are small have tiny feces, and the pathogens die off quickly. So, farmers don’t have to know the species of bird it came from. They just need to know the size. If it’s the size of a quarter, don’t harvest near that. If it’s a tiny white speck, it’s very low risk and probably fine.”

I don’t see farmers deliberately looking for bird poop that’s the size of quarter in a 500-acre field, but Kerlin reported about 90% of birds observed on the farms were small and tended to poop mostly on soil, which means growers of leafy greens should be able to harvest about 10% more of their fields.

And that’s good news for both farmers and anyone who eats.

Jim Smith is the former editor of The Daily Democrat, retiring in 2021 after a 27-year career at the paper.