The Tivoli Bays are the only large fresh-tidal marshes on the Hudson
River primarily bordered by undeveloped forest. Tivoli North Bay
is a freshwater tidal marsh dominated by cattail; Tivoli South Bay
includes vegetated tidal shallows (mudflats at low tide). The site is an
important spawning and nursery ground for a variety of anadromous
and freshwater fish species. Map turtle (Graptemys geographica) and
American brook lamprey (Lampetra appendix), both rare in New
York, occur at the site. The site hosts a number of rare plant species
including estuary beggar ticks (Bidens bidentoides and B. hyperborea),
ovate spikerush (Eleocharis ovata), Eaton?s bur-marigold (Bidens
eatoni), winged monkey flower (Mimulus alatus), and swamp lousewort
(Pedicularis lanceolata). The site is primarily administered by NYS
DEC and the New York State Office of General Services, but contains
several small, privately owned parcels as well.

Ornithological Summary

Species documented as breeders include the Least Bittern (estimates
from 1970s suggested dozens of pairs, recent numbers are probably
similar), Virginia Rail, Sora (apparently bred until mid-1970s),
Common Moorhen (apparently bred until mid-1970s or 1980s), and
Marsh Wren (estimates from 1970s suggested a thousand individuals,
recent numbers are probably similar). The site is one of the last known
areas for King Rails in the state. The area is used by large flocks of
dabbling ducks in the spring and fall, with good numbers of American
Black Ducks (peak estimates of 100-200 individuals). Bald Eagles forage
at this site year round, and Ospreys and Northern Harriers regularly
forage during migration. Large fall post-breeding concentrations of
swallows possibly reach 10,000 individuals.

Conservation Issues

This site is listed in the 2002 Open Space Conservation Plan as
a priority site under the project name Hudson River Corridor
Estuary and Greenway Trail. Common reed (Phragmites australis)
covers approximately one percent of North Bay and is spreading;
management is being debated but is not currently practiced. Eurasian
water chestnut (Trapa natans) dominates South Bay and is very minor
in North Bay; no control is currently practiced due to concerns
about non-target impacts of herbicides. Purple loosestrife (Lythrum
salicaria) has been declining. Potential pollution leaching from a
nearby landfill (now closed) should be monitored. Better inventory
and monitoring of the marsh birds are needed.

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