Colonial Waterbirds

Nesting Pairs at CT and NY (including Long Island and NYC) sites
Snowy Egret Great Egret Black-Crowned
Night Heron
1998 693 728 1637
2001 627 813 1443
2004 826 945 1714
2007 608 867 1363
2010 552 1230 1591

What are colonial waterbirds?

Colonial waterbirds, particularly long-legged wading birds noted here, nest primarily in groups on islands along the Atlantic coast. They typically nest within scrub-shrub and woodland habitats, and often feed on estuarine fish and invertebrates in nearby salt marshes. Nesting data (i.e., breeding pairs) is provided above for three species that feed in tidal marshes: Snowy Egrets, Great Egrets, and Black-crowned Night Herons.

What does this indicate?

Colonial Waterbirds feed on estuarine fish and invertebrates in salt marshes. Therefore, these bird populations indicate the success of the salt marshes in providing a habitat for the colonial waterbirds’ prey. Colonial waterbirds nest in coastal forest areas and therefore their population numbers indicate to some degree the health and abundance of coastal forests.

Status

Colonial waterbirds, particularly long-legged wading birds, such as snowy egrets, great egrets, and black-crowned night-herons, nest primarily in groups on islands along the Atlantic coast. They typically nest within shrub and woodland habitats, and often feed on estuarine fish and invertebrates in nearby salt marshes. Although the populations have been relatively steady since 1998, there has been a relative decline in snowy egrets and night-herons since the 1970s, which may be due to predation by animals associated with humans, including rats and feral cats; additionally, a loss of nesting habitat, including that from human disturbance, a loss of wetlands important for feeding, and exposure to contaminants may have contributed to the declines. The trend of decline in the population of Black-crowned Night Herons since 1998 is also likely due in part to losses in habitat as exemplified on Pralls Island (see data note below).

The numbers of colonial waterbirds tend to fluctuate becauseĀ they typically do not show strong nest site fidelity, which results in fluctuations if a single site is monitored over a period of time.

Data Notes

A data estimate was used for a missing Brother Island count in 1998. Pralls Island, just west of Staten Island, NYC was cleared of trees in March 2007 in response to an outbreak of the invasive Asian long-horned beetle. In 2004, on Pralls Island, there were no Snowy Egrets or Great Egrets nesting. There were 15 Black-crowned Night Herons.

While Pralls Island and several other data collection sites are technically outside of the Long Island Sound watershed, they were included in this study and indicator because the foraging distance for these animals is short enough that they can, and do, access Long Island Sound while nesting. In addition bird colonies wax and wane from year to year. This may not be due to an increase or decrease in bird numbers but due to shifts in nesting location. So, waterbirds nesting in NYC Harbor one year could end up in the west end of Long Island Sound in another year.

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