By Science Director Maddy Schwarz
‘Twas the day before New Year’s and all through the house, biologists were typing and rereading paragraphs aloud…
It’s a cruel fact that projects are often due on the last day of the month, meaning that if it was a year-long project, it’s due on the last day of the year. Therefore, before you head out to your New Year’s Eve festivities, you must first cobble together whatever brainpower survived the onslaught of holiday cookies and poor sleep decisions during the week between Christmas and New Year’s and submit! that! final! report! While generally not anyone’s preferred New Year’s Eve activity, if you’re lucky, the project you’re finishing is interesting and worthwhile. The kind of project that makes you reflect on what you accomplished during the year, appreciate how much you learned, who you worked with, and how your efforts illuminated a new corner of the world you hadn’t considered before.
Happily, this was the case for the project I was finishing on New Year’s Eve 2025. The Plover and Tern Program at SFBBO received a Section 6 grant from the US Fish and Wildlife Service and the California Department of Fish and Wildlife in August 2024 that provided funding for our biologists to deploy Motus tags on western snowy plovers at Eden Landing Ecological Reserve in Hayward. Although Motus tags have been used on snowy plovers in the Great Salt Lake and Mexico, our project is the first one to deploy them on the federally listed population. We were also testing an aspect of the technology that would allow us to track finescale movement within individual ponds. We partnered with two additional snowy plover biologists in the Bay, Ben Pearl, who longtime readers may recognize as the former Plover and Tern Program Director at SFBBO, and Carleton Eyster, a renowned plover biologist who has been studying the species since the 1990s.
After a year of hard work that involved 12-hour build days, walking 40 grams of raw chicken on the end of a tripod across Eden Landing, waiting at nests until 1am to capture adult male plovers, and sorting through 5 million lines of data, we had arrived at the finish line. What did we have to show? Many interesting things!
Incubating plovers spend a lot of time at their nest. On first glance, this seems obvious. Of course they’re spending a lot of time at their nest, where else would they be? But plover pairs typically divide their incubation duties into shifts. The males are supposed to incubate at night and the females are supposed to incubate during the day. This allows the other sex to leave and forage or roost for half the day. During our regular daytime surveys, we usually observe the female on the nest by herself and the male is nowhere to be found. However, the Motus data showed that while the other adult did leave and forage when they weren’t incubating, they still spent a lot of their “free time” near the nest. This also allowed them to sneak in short incubation stints even when they weren’t “supposed” to be incubating. This shows that the day/night split between females and males is not so straightforward and is likely unique to each pair.
Figure 1: Flight path of the banded snowy plover female, Ka:wr, showing her journey from Eden Landing in Hayward, California to Bolinas, California.
Plovers really love water! A trend we noticed immediately is that when birds weren’t at their nests, they were finding a wet area of a pond to forage along. This makes sense when you consider that plovers are shorebirds. They’re adapted to eat small invertebrates that occur along the tideline. It makes perfect sense that they would seek out the water’s edge on salt ponds as well. SFBBO has always understood that good foraging habitat includes water, but this project really helped us visualize just how much time plovers spend foraging. The plover program is primarily focused on ensuring plovers have adequate breeding habitat in the Bay Area, and while that is definitely still important, this project has inspired us to think about foraging habitat more intently as well.
And finally, some of the birds we tagged went to many different places! The Motus tags that we used don’t just tell us information about where individuals are in Eden Landing, they can also ping any other Motus tower in the world. From pings we received from towers outside Eden Landing, we know that our birds have gone to Point Reyes, China Camp State Park, Don Edwards National Wildlife Refuge, Milpitas, Napa-Sonoma Marshes Wildlife Area, and the Channel Islands! We have always known that plovers disperse to a variety of areas in the winter, but it was so exciting to see just how many different places they went.
Figure 2: Series of heat maps showing the locations of a banded, incubating pair (male Gk:og, female Ka:wr) split into daytime and nighttime. The maps show that both adults spend the majority of their time at the nest during a 24-hour cycle, but that the female will forage in additional areas during the night and the male will forage in additional areas during the day.
As a biologist, I spend so much time staring through a scope, hoping to get a quick peek into a plover’s life, knowing that it is only a tiny snapshot, and accepting that I will never get to see the vast majority of their life. It’s not that typical survey methods don’t work or are inadequate: I am consistently amazed by how much information we’re able to acquire from a weekly survey alone. But when the opportunity comes along to crack open the puzzle a little wider and peer into the vast network of interactions we call ecology, it’s impossible not to feel the excitement. The maps that we generated from the Motus data and included in the final report for this project took an astronomical quantity of information and condensed it into a representation that our human brains can easily interpret. When I look at one of these maps and understand the habits of a tiny bird that I may have never seen with my own eyes, it feels like magic.
