Elkhorn Slough National Estuarine Research Reserve: Monitoring waterbirds
Data files
Oct 28, 2025 version files 1.45 MB
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Data_Curation_Areas_Oct2024.kmz
1.04 MB
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Elkhorn_Slough_Waterbirds.csv
386.94 KB
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README.md
3.91 KB
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Waterbirds_survey_sites.kmz
16.19 KB
Abstract
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).
Dataset DOI: 10.5061/dryad.j3tx95xv2
Files and variables:
File: Data_Curation_Areas_Oct2024.kmz
Description: This is a Google Earth file showing how the Elkhorn Slough National Estuarine Research Reserve subdivides the estuary into regions and areas that are included as columns in the dataset
File: Waterbirds_survey_sites.kmz
Description: Google Earth file of the waterbird survey site areas
File: Elkhorn_Slough_Waterbirds.csv
Description: Waterbird count data
Variables
- Date: Survey date
- Year: Survey year
- Month: Survey month
- Day: Survey day
- Month_1: Survey month
- Season: Meteorological season
- Oceanographic_season: Upwelling (March-August), Oceanic (September-October), Davidson (November-February)
- Subregion: finer categorization of region used by ESNERR; for waterbirds surveys specifically, the boundary between Main Channel - Section C and D - separates Lower from Upper Slough, respectively; see KMZ file provided separately
- Area: Parsons Slough complex (Parsons Slough, Oak Marsh/Shark Flats), Pelican Marsh complex (Pelican Marsh, Estrada), Main Channel (Sections A-E)
- Start_time: Survey start time
- End_time: Survey end time
- Common_Loon:
- Pacific_Loon:
- Red-throated_Loon:
- Pacific/red-throated_Loon: Additional counts of PALO/RTLO not identified to species
- Pied_billed_Grebe:
- Horned_Grebe:
- Eared_Grebe:
- Horned/Eared_Grebe: Additional counts of HOGR/EAGR not identified to species
- Western_Grebe:
- Clark's_Grebe:
- Western/Clark's_Grebe: Additional counts of WEGR/CLGE not identified to species
- White_Pelican:
- Brown_Pelican:
- Double-crested_cormorant:
- Brandt's_cormorant:
- Pelagic_cormorant:
- Cormorant_sp: Additional counts of cormorants not identified to species
- Great_Blue_Heron:
- Green_Heron:
- Black-crowned_Night_Heron:
- Great_Egret:
- Snowy_Egret:
- Canada_Goose:
- Brant:
- Duck_sp: Additional counts of ducks not identified to species
- Mallard:
- Northern_Pintail:
- Green-winged_Teal:
- Blue-winged_Teal:
- Cinnamon_Teal:
- Northern_Shoveler:
- Gadwall:
- American_Wigeon:
- Canvasback:
- Ring-necked_Duck:
- Greater_Scaup:
- Lesser_Scaup:
- Scaup _sp: Additional counts of Scaup not identified to species
- Surf_Scoter:
- White-winged_Scoter:
- Scoter_sp: Additional counts of Scoter not identified to species
- Common_Goldeneye:
- Bufflehead:
- Red-breasted_Merganser:
- Ruddy_Duck:
- American_Coot:
- Black-bellied_Plover:
- Snowy_Plover:
- Semipalmated_Plover:
- Killdeer:
- Black-necked_Stilt:
- American_Avocet:
- Greater_Yellowlegs:
- Lesser_Yellowlegs:
- Yellowlegs_sp: Additional counts of yellowlegs not identified to species
- Willet:
- Spotted_Sandpiper:
- Western_Sandpiper:
- Least_Sandpiper:
- (Western/Least_sandpiper): Additional counts of WESA/LESA not identified to species
- Whimbrel:
- Long-billed_Curlew:
- Marbled_Godwit:
- Ruddy_Turnstone:
- Sanderling:
- Dunlin:
- Short-billed_Dowitcher:
- Long-billed_Dowitcher:
- Dowitcher_sp: Additional counts of dowitcher not identified to species
- Shorebirds_small_unidentified: Additional counts of small shorebirds not identified to species
- Shorebirds_large_unidentified: Additional counts of large shorebirds not identified to species
- Wilson's_Phalarope:
- Red-necked_Phalarope:
- Bonaparte's_Gull:
- Heerman's_Gull:
- Mew_Gull:
- Ring-billed_Gull:
- California_Gull:
- California/ring-billed_Gull: Additional counts of CAGU/RBGU not identified to species
- Herring_Gull:
- Thayer's_Gull:
- Western_Gull:
- Herring/Western_Gull: Additional counts of HEGU/WEGU not identified to species
- Glaucous-winged_Gull:
- Gull_sp: Additional counts of gulls not identified to species
- Forster's_Tern:
- Elegant_Tern:
- Caspian_Tern:
n/a represents missing data - sites/dates where no surveys were conducted
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.