The harvest of silage, an important way some ranches curb costs and reduce their carbon footprints, impacts birds at three dairies in the Point Reyes National Seashore, according to a study released in December by Point Blue Conservation Science, a research-based nonprofit.
The seashore commissioned the study as part of the planning process for its ranching management plan, which will establish how it manages free-ranging elk and ranching practices. The latter issues range from succession, rules for various ranch operations and diversification, which includes whether and to what extent ranches can expand beyond beef and dairy operations to activities such as row crops, cheesemaking and silage.
B Ranch, for example, which is run by Jarrod Mendoza, wants to start growing silage.
“No matter what we do with silage, we need to look at proposed impacts…Do we reduce it, keep it the same or allow for an expansion?” said Dave Press, a wildlife ecologist for the seashore.
Ranches grow and harvest silage—stored, fermented grass—to feed to cattle as a supplement to forage. “Almost every dairy in the country has to provide feed that supplements grazing for part of the year,” Bob McClure, of I Ranch, said in an email to the Light. “There isn’t enough grass, or high enough quality grass, to maintain milk production [the entire year] without supplemental feed. Here at Pt. Reyes, we especially need to provide supplemental feed in the summer and fall dry seasons and early winter before grass recovers.”
In the first half of the 20th century, many seashore ranches grew hay, Mr. McClure said. But they switched to purchasing it from the Central Valley in the 1950s, in part because the local climate is poor for hay, which can mold because of the fog.
Hay became increasingly expensive and, over 40 years ago, a few dairies in the seashore started growing silage as an alternative.
“It’s the perfect solution for us because it has to be cut while it is still green—fog and rain are not problematic,” Mr. McClure wrote.
Growing silage reduces feed costs, which can be high. In 2014, the late Joey Mendoza, of B Ranch, wrote in his scoping comments for the ranching plan that 70 percent of costs at dairies go toward feed. A decade earlier, it was closer to 50 percent.
And silage is especially helpful for organic dairies, Mr. McClure said. Organic hay is not only expensive but increasingly difficult to find in California, as more dairies switch to organic and demand rises.
Silage growers also argue that it reduces the farm’s carbon footprint: Mr. McClure said his ranch would need to truck in 60 more loads of hay a year were it not to grow silage. In total, he estimated that ranches grow silage on about 900 of the 28,000 acres of ranch land administered by the seashore.
In their scoping comments, Tim and Janice Kehoe, of J Ranch, said silage reduces their greenhouse gas emissions. They specifically requested that the ranching plan allow ranchers to use up to 25 percent of their leased lands to grow it.
Yet mowing silage, which takes place in the spring, is known to kill nesting birds. That presents a significant concern in a federal park where resource protection is pivotal.
“Several studies have found that the agricultural practice of mowing (whether for silage or hay) has detrimental impacts to breeding birds because nests, flightless young, and sometimes adults are destroyed,” the Point Blue study said.
In the Environmental Action Committee of West Marin’s scoping comments in 2014, then-executive director Amy Trainer wrote, “Silage production kills hundreds of nesting birds per year. EAC would not support expanded silage production.”
To examine the impact of silage mowing on birds that breed locally, as well as the types of birds that breed here, Point Blue researchers set up study plots at three ranches that grow silage: H, I and J Ranches. It also set up study plots at B Ranch, which is hoping to start growing silage once the ranch plan is complete.
Researchers visited the plots before the spring mowing to determine the abundance of birds—that is, how many birds they could find in a small area in about 20 minutes—as well as what types of birds were found in each study site. (Researchers didn’t monitor nests closely, but instead took note of nests that they happened upon.)
Study plots on ranches were established in areas where silage is grown as well as other areas on the ranch where silage is not grown, for comparison purposes.
The researchers found that before mowing took place, bird abundance was relatively similar in both silage and non-silage areas on the ranch.
However, silage areas featured more species that the study deemed “focal species,” or birds that were either seen nesting, or were likely to be breeding, in the silage field and are considered “species of conservation concern” by the state. That includes species like the red-winged blackbird, song sparrow, savannah sparrow and northern harrier.
Researchers hypothesized that the wild mustard and wild radish amidst the tall silage grasses attract the birds, as the weeds create ideal nesting habitat.
But after the silage study plots were mowed, both species abundance and species richness—how many species were counted during monitoring—fell. For instance, before mowing, the silage fields had an average of 35 birds per 10 hectares, but afterwards averaged 18 per 10 hectares. Meanwhile, in the non-silage study areas, abundance and richness rose somewhat.
Though the study didn’t rigorously examine nests, researchers observed four species nesting in the silage areas before mowing and found evidence that four additional species were also nesting there. After the mowing, they found just two species potentially nesting in the area.
B Ranch, which wants to grow silage, didn’t have as much species diversity as the other ranches, but the study found it harbored a strong number of savannah sparrows.
“The study sort of confirmed what we had anecdotally been noticing,” Mr. Press said of the results. “Clearly some nesting is happening within those silage fields and then there’s a lack of bird abundance once it’s cut.”
Ryan DiGaudio, one of the Point Blue researchers, wasn’t surprised by the results. “No matter how you do it, there’s going to be some impact when there’s mowing occurring during the nesting season. So timing is everything…We’re trying to figure out a way that silage can be harvested at a time when it has the least impact on nesting birds,” he said.
The study concluded with a list of potential ways to minimize impacts. It is not feasible to delay mowing until after the nesting season ends in July, as the silage would wither by then, but it may be possible to mow later in the nesting season.
Last week, the researchers met with the Point Reyes Seashore Ranchers Association to discuss the results of the study.
“I think we’re pretty upfront about this in our report: at Point Blue, we’re experts at studying birds, but we’re not experts on managing silage,” Mr. DiGaudio went on. “One idea that I think had some promise [at the meeting] was adjusting the timing as much as ranchers could, with regard to harvesting crop and the crop still being worthwhile.”
Mr. McClure said impacts on birds, while inevitable, can likely be curtailed. “I can’t think of any agricultural practice that doesn’t have some impact on natural resources,” he wrote to the Light. “The challenge for ranchers and farmers, especially for us in the seashore, is to develop best practices that minimize those impacts. One value of the Ranch Comprehensive Management Plan process is that it’s providing a mechanism for us to work with seashore staff on designing, testing, and adopting techniques that will be recognized as best practices.”
The researchers will study the same plots again this spring to gather more data. Last year, ranchers mowed over a month earlier than usual because of the drought, but this year they could likely mow later, thanks to the winter rains.