Elkhorn Slough National Estuarine Research Reserve: Monitoring waterbirds

The purpose of this monitoring is to track migratory and resident shorebirds, waders, and waterfowl using the tidal wetlands of Elkhorn Slough in central California, USA. While this modest program will not be sufficient to detect subtle alterations, we will be able to detect dramatic changes. By comparing our results to those from other wetlands along the coast, we can determine whether the changes are due to local factors affecting only the Slough (loss of foraging areas due to tidal scour, elimination of prey due to oil spill, etc.) or regional processes affecting the whole coast (breeding failure, El Niño effects on prey recruitment, etc.). Elkhorn Slough National Estuarine Research Reserve teams have been counting waterbirds since 2003 to the present (2025 at current data submission).

Methods
Using spotting scopes and binoculars, surveys are conducted during peak migration, once or twice in the fall (September and November) and once or twice in the spring (early-mid March, mid-late April). Surveys take place during spring tides, within 2 hours of low tide listed between +2.0 and -1.5 ft. We submit our November survey data to Point Blue as part of their annual Pacific Flyway Shorebird Survey (PFSS). 

Four sites are surveyed on the same day (or within a few days of each other), coinciding with the low tide: Main Channel (by boat), North Harbor/Bennett Slough West, Parsons Slough, and Oak Marsh/Shark Flats; one site (Pelican Marsh/Estrada) is surveyed on the same day at high tide.

Main Channel: from the Hwy 1 bridge to Hudson Landing. Divided into 4 sections (Section A-E), each of which is surveyed separately; see additional information below.

We used cell phones to communicate between the two boats to avoid double counting (particularly grebes and terns in center of channel) – one boat surveys waterbirds on the north bank and the other boat surveys the south bank. Bring Kvitek bathymetry GIS for difficult navigation from Kirby to Hudson. Start the survey at the Hwy 1 bridge and work up towards Hudson.

Section A – Bridge to Dairy

Section B – Dairy to mouth of Parsons Slough

Section C – Parsons Slough mouth to Coyote Island

Section D – Coyote Island to Kirby Park Dock

Section E – Kirby Park Dock to Hudson Landing Bridge

North Harbor/Bennett Slough West: on mudflats off Jetty Road, Moss Landing State Beach. Survey the mud/sand flats on the northern half of North Harbor (from the seal haul out, all the way to Jetty Rd), from various vantage points, as well the southern portion of Bennett Slough West.

Parsons Slough: at ESNERR, near end of Parsons Overlook trail. Walk down peninsula at end of trail and gradually walk about 20 m to either side of point; survey mudflats visible from this area.

Oak Marsh/Shark Flats: at ESNERR, on either side of berm just past footbridge on Oak Marsh loop trail. Survey Oak Marsh, and Shark Flats on other side. (Note: this site surveyed from 2003 – 2018 only).

Pelican Marsh/Estrada: at ESNERR, from water monitoring station at tide gates, on road running down from Pelican Marsh Overlook. Survey areas visible from this vantage point. Then drive to Estrada Overlook and survey Estrada Marsh.