Long-term Coastal Breeding Bird Monitoring in the Boston Harbor Islands, 2007-2019

The National Park Service with support from numerous partners and community volunteers, has implemented long-term monitoring of coastal breeding birds in the Boston Harbor Islands since 2007. The objectives of the monitoring are to assess long-term trends in the abundance of priority coastal breeding species among the islands to inform conservation practices and park management. A combination of boat- and ground-based surveys are used to estimate the number of incubating Larus argentatus (Herring Gull), Larus marinus (Great Black-backed Gull), Phalacrocorax auritus (Double-crested Cormorant). Haematopus palliatus (American Oystercatcher), Somateria mollissima (Common Eider), and tern species annually. Ground-based nest counts are conducted for Common Eider and wading birds (Plegadis falcinellus [Glossy Ibis], Nycticorax nycticorax [Black-crowned Night Heron], Ardea alba [Great Egret] and Egretta thula [Snowy Egret]) on a 2-3-year rotation on islands that are accessible for landing by boat. The objectives of this study were to present count data from this monitoring and assess trends in annual counts of cormorants. gulls, and eiders estimated during boat-based surveys from 2007 to 2019. Changes in annual nesting of Double-crested Cormorants, Herring Gulls, and Great Black-backed Gulls estimated by boat-based surveys varied over time and by island, but in the park overall, all 3 species appear to have stable breeding colonies. Boat-based monitoring indicates that counts of tending Common Eider females and ducklings are declining in the areas where they forage near the Outer Islands. Ground-based monitoring has indicated that the largest wading-bird colony has consistently been located on Sarah Island and that Black-crowned Night Herons are the dominant driver in overall numbers and on all islands, except for Sheep Island. where they were overshadowed by an increase in Snowy Egrets in 2016 and 2018. As the long-term monitoring continues, we intend to compare its results to historical and regional data to better understand how populations have and are responding to environmental change in the harbor and to better understand how coastal breeding birds utilize natural communities within the park to inform park management decision-making.

Automated summary

The National Park Service, along with partners and volunteers, has been monitoring coastal breeding birds in the Boston Harbor Islands since 2007. The monitoring aims to assess long-term trends in bird populations among the islands to inform conservation practices and park management.