Elkhorn Slough National Estuarine Research Reserve: Monitoring rookery of nesting herons, egrets and cormorants

The purpose of this monitoring is to track the number of tree-nesting ardeids and phalacrocoracids adjacent to the Elkhorn Slough estuary in central California, USA.  Three species nest together in large rookeries in trees on the banks of the Elkhorn Slough estuary: great blue herons, great egrets, and double-crested cormorants.  Elkhorn Slough National Estuarine Research Reserve teams have been counting nests since 1985 to the present (2025 at current data submission)., Teams of ESNERR staff members, volunteers, and associated students counted nests using binoculars and spotting scopes. The number of active nests belonging to each species was counted from one or multiple vantage points beneath the trees that were being used.  Nests of each species are fairly distinctive (cormorants have more eelgrass/leaves woven in, heron nests are the largest and full of twigs, etc.), and the surveys were conducted in late Spring when chicks were in or near the nests. The numbers reported are likely to be underestimates, especially for the smaller cormorant and egret nests, because some nests are on the back side of the trees relative to the observer vantage points. The exact locations of the rookery in different periods are provided in an associated file called Rookery_Metadata_Sites.csv
From 1985-2008, the rookery was located in a grove of Monterey pines on the main Elkhorn Slough Reserve, in an area bordered by the Oak Marsh Trail, the Rookery pond, and the s..., # Elkhorn Slough National Estuarine Research Reserve: Monitoring rookery of nesting herons, egrets and cormorants

Dataset DOI: [10.5061/dryad.h9w0vt4vw](10.5061/dryad.h9w0vt4vw)

## Description of the data and file structure

Teams of ESNERR staff members, volunteers, and associated students counted nests using binoculars and spotting scopes. The number of active nests belonging to each species was counted from one or multiple vantage points beneath the trees that were being used.  Nests of each species are fairly distinctive (cormorants have more eelgrass/leaves woven in, heron nests are the largest and full of twigs, etc.), and the surveys were conducted in late Spring when chicks were in or near the nests. The numbers reported are likely to be underestimates, especially for the smaller cormorant and egret nests, because some nests are on the back side of the trees relative to the observer vantage points.

### Files and variables

#### File: Rookery.csv

**Description:** Nest count d...,