A Study on Phalarope Foraging Habits to Inform Phalarope Conservation

By Director of Waterbird Science Nathan VanSchmidt

​SFBBO staff and volunteers are out in the current and former salt ponds of South San Francisco Bay and watching some of the most interesting shorebirds as they stop by during this summer migration: Wilson's Phalaropes and Red-necked Phalaropes. Surveys undertaken over the past five years have found a species in a long-term ongoing population collapse, with contemporary counts 98% lower than the more than 40,000 birds observed in the 1980s and more than 50% lower than counts in the early 2000s.

These unique saline-specialist shorebirds stop in San Francisco Bay--as well as saline lakes throughout the Great Basin like Mono Lake, Lake Abert, and the Great Salt Lake--to forage and fatten up early in migration before making the rest of the long trip to their wintering grounds in South America. 

The most obvious explanation for their decline is that the transition of ponds managed for commercial salt production into lower-salinity ponds managed for wildlife under the South Bay Salt 

Pond Restoration Project may have reduced the habitat suitability of the South Bay for the saline-specialist phalaropes, even as it greatly benefitted many other waterbird species. However, preliminary data does not show this to be the case.

Mysteriously, in recent years phalaropes have been much more abundant in the low-salinity wetlands--the opposite of what you'd expect! There is still evidence that Red-necked Phalaropes, who are more generalist in their habitat preferences, have adapted better to the changes in restoration ponds than Wilson’s Phalaropes, who are more specialized in saline lakes, have. Red-necked Phalaropes showed rapid decline in both restoration project ponds and salt production ponds in the 2000s, but were almost entirely extirpated from salt production ponds while they persisted in restoration project ponds . In contrast, Wilson’s Phalaropes had been almost wholly extirpated from restoration project ponds by the 2010s, while they persisted in salt production ponds.

To uncover what may be driving the decline and the current trends in where phalaropes are found on the landscape, SFBBO has launched a new research project with our volunteer surveyors this spring. In addition to counting phalaropes, staff and volunteers are also doing behavioral observations of their foraging ecology--counting the number of times they peck at the surface in each pond, and the number of times they can be observed swallowing. Counterintuitively, they swallow by opening their beaks--each invertebrate is captured in a bead of water, which is pulled to the back of their long beak by surface tension when they open it, which allows us to relatively easily count how many times they catch prey each minute!

We've already seen some big differences between ponds, with Wilson's Phalarope in Sunnyvale feeding so rapidly that individual pecks could scarcely be counted - a motion SFBBO volunteer Pete Dunten accurately described as like a the beak acting like a "sewing machine" cutting through the water. 

You can view the video here.

If you slow it down to 0.25x speed, you can see the birds opening their beak after each peck.

This observation was indeed at one of our low-salinity ponds, so we're hopeful that this research may provide some useful insights. SFBBO is also planning to pilot invertebrate sampling at some of these ponds so we have some idea what the birds might be feeding on with these different foraging behaviors.

Trends from last summer and early counts from this year have shown higher than usual phalarope abundances - not quite back up to their historic levels in the mid-2000s, but higher than any other recent years! With the new data we gather this summer, we hope to help identify habitat conditions that can allow these shorebirds to thrive in the Bay Area and beyond, and help land managers keep their populations on an upward trajectory.