Endangered shorebirds benefit from invasive weed control partnership

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Milestone® herbicide has been used to maintain critical shorebird nesting sites in the East Bay Regional Park District since 2012. Without it, birds migrating back here to nest would be crowded out by invasive plants and subject to predators.

Just east of San Francisco is the East Bay Regional Park District. Encompassing 125,000 acres, including 73 parks and 1,250 miles of trails, it serves as a recreation refuge for residents and visitors who enjoy hiking, biking, fishing, camping and a variety of other outdoor activities.

East Bay Regional Park District also serves as a refuge to a variety of wildlife, including endangered nesting shorebirds. One park in particular, Hayward Regional Shoreline, is utilized by more than 20 species of nesting shorebirds, including the California least tern, which was listed as a federally endangered species in 1970.

Hayward Regional Shoreline is a 145-acre fresh and brackish water marsh made up of five managed ponds and 15 islands. Island Five — or Tern Town, as it’s called — became home to one of the most productive least tern colonies in Northern California after having been restored by more than 4,000 volunteers who moved more than 200 tons of sand and oyster shells to create the island’s ideal nesting habitat.


Back in 2009, invasive plants threatened to undo all the hard work and progress made. David Riensche, a wildlife biologist affectionately referred to as Doc Quack, leads volunteer efforts around the nesting sites for the park.

“When invasive species are allowed to spread, they will quickly cause these sensitive island nesting areas to become substandard,” Riensche says. “Their presence also encourages other species of birds to nest on the site, which not only crowds out least tern nests, but we believe encourages predators like foxes and raccoons to swim to the island to attack the nests.”

That’s exactly what played out on Island Five.

“Weeds made it ashore thanks to a mix of coastal flooding and via the soil used to construct the island, which was contaminated with seeds,” says Casey Brierley, an Integrated Pest Management specialist in the stewardship department for parks in the East Bay Regional Park District. “It resulted in mayweed chamomile rapidly spreading to become the dominant plant cover and confining the terns to less-than-ideal nesting sites.”

Things got even worse when other bird species, such as mallard and cinnamon teal, started utilizing the fresh plant cover to establish nests of their own. “The combination of limited nest site availability and the increased presence of predators led to a reduction in the number of successful reproductions from least terns,” Riensche adds.


In 2012, a partnership was formed between Corteva Agriscience, Caltrans and the East Bay Regional Park District to address the overgrowth using careful herbicide treatments.

Corteva Agriscience contributed a combination of Milestone®, Capstone®, Rodeo® and Dimension® herbicides, prescribed by Rick Miller, Vegetation Management specialist with Corteva Agriscience. Each have been proven to be “practically nontoxic” in laboratory testing. Bill Nantt, landscape specialist with Caltrans, contributed equipment, manpower and materials.

The least terns, and the surrounding ecosystem, were unharmed by the use of these herbicides, which were carefully applied by trained applicators. “We quickly saw positive effects on these special status birds, and they have grown to become the second-largest least tern colony north of Ventura County,” Riensche says.



Today, the partnership endures — still keeping weeds at bay to protect this critical nesting habitat. Beau Miller, Vegetation Management specialist with Corteva Agriscience, has since transitioned to making the herbicide recommendations, but the positive results remain consistent.

“Even in what’s been a really wet year for us, Milestone delivered 90% control on the mayweed chamomile,” Brierley says. “Lots of rainfall can make it especially tough to get good results because the treatment surface is a mix of crushed oyster shells and sand, and therefore doesn’t hold herbicide very well.”

Brierley, who recently retired, continues working on the project. Only now, it’s as part of Doc Quack’s Wildlife Volunteers — a team of dedicated people striving to improve the quality of life for birds and other wildlife in the East Bay Regional Park District.

The ongoing work to keep invasive vegetation from destroying this critical habitat aims to keep Tern Town and all the Hayward Regional Shoreline as a viable and thriving nesting location for this endangered species. Wildlife experts, like Riensche, look forward to continued population growth.


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