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colonies. Cumulatively, the lack of terrestrial predators (primarily raccoons),
minimal amount of human disturbance, lack of parasites and disease, and the
presence and availability of prey items all likely contribute to the continued
viability of individual nesting sites (Lorenz et. al., 2002).
Spoonbills forage in shallow marine, brackish and freshwater sites, including
tidal ponds, and sloughs, mud flats, mangrove-dominated pools, freshwater
sloughs and marshes and man-made impoundments (R. Bjork, 1996).
Mangrove-dominated shorelines and the marine-estuarine transition zone
have been documented as the primary foraging areas used by the spoonbills
that nest in Florida Bay. The dwarf mangrove community that is present in
areas where there is little soil accumulation overlaying a rock substrate
appears to provide valuable foraging habitat for spoonbills.
Spoonbills forage in shallow by sweeping a partially-open bill back and forth
in a semi-circular motion while slowly walking forward in search of small
prey items. When the bill strikes a prey item, it immediately snaps shut; a
process known as tactolocation. This unusual foraging strategy is successful
only when water depths are less than 20 cm (Lorenz, 2000). Investigations
regarding prey items (Allen, 1942, Dumas, 2000, Lorenz et. al., 2002) indicate
that small fishes, including sheepshead minnows (Cyprinodon variegatus),
sailfin mollies (Poecilia latipinna) are the primary prey items. Shrimp
(Palaemonetes sp.) are also taken.
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-18
Annual wet season and dry season water level fluctuations that are typically
present in south Florida are critical to the nesting success of many wading
birds, including spoonbills. Their annual nesting cycle is timed around the
decreasing water levels that are associated with the winter-spring dry season.
Foraging by adults is most effective during this period, when the population
of prey, which has increased during the wet season, becomes concentrated as
surface waters diminish.
Although most spoonbills nest on islands in Florida Bay, they make daily
flights to foraging areas to mainland wetlands north of Florida Bay. By
conducting studies of flight distance from nesting sites during 1989-90,
Lorenz, et. al. (2002), documented that the mean flight distance for spoonbills
nesting in Florida Bay was 12.4 km + 5.8 km (mean + standard deviation),
with approximately 83% of the flights being less than 16 km.
Recent studies by Lorenz (1999, 2000) in Florida Bay have revealed that
comparatively higher, and more variable salinities in the same coastal
wetlands has resulted in reduced prey biomass for foraging spoonbills.
Additionally, long-term studies of spoonbill nesting territories indicates that
spoonbills do respond to the destruction or degradation of their foraging
grounds by relocating to other areas in closer proximity to suitable foraging
areas. For these reasons, spoonbills appear to be an excellent indicator of
ecosystem health for southern Biscayne Bay, as indicated by the maintenance
of a nesting population adjacent to the Bay. Maintaining suitable foraging
habitat for spoonbills may also contribute to the success of spoonbills and
other bird species that nest outside the boundary of the project area
Additionally, because a variety of other vertebrate predators, including
piscivorous fishes, reptiles and wading birds also depend on the same prey
items, the continued presence of spoonbills will likely also indicate success
for other species.
West Indian Manatee
West Indian manatees are large, herbivorous, air-breathing aquatic mammals
that can be found within suitable habitat throughout much of peninsular
Florida. They are protected pursuant to the Florida Wildlife Code and the
federal Endangered Species Act, as amended. Their current designation at
both levels is ‘endangered’, although the Florida Fish and Wildlife
Conservation Commission is considering a ‘downlisting’ to threatened. An
initial federal recovery plan for this species was developed in 1996, and the
Multi-species Recovery Plan for South Florida (USFWS, 1999), contributed
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-19
information pertinent to South Florida and Biscayne Bay. Critical habitat was
designated for this species in the early 1970s as areas occupied by manatees
‘which have those physical or biological features essential to the conservation
of the manatee and/or which may require species management
considerations”. No specific locations, maps or other descriptions were
provided to more specifically define critical habitat.
Miami-Dade County was one of 13 key counties that were required by the
State of Florida to develop a county-specific Manatee Protection Plan (MPP).
That Plan, DERM Technical Report 95-5 (DERM 1995), provides extensive
information regarding manatees in Miami-Dade County, including sections
on: habitat, manatee-human Interaction, local land development, education
and awareness, governmental coordination and habitat protection. The MPP
was approved by the State of Florida on December 21, 1995.
Manatees potentially inhabit all areas of Biscayne Bay. Depending on the
design of any individual water control structure, manatees may also travel
upstream of these structures. Although manatees may be present in the Bay
during any month of the year, they are most numerous in Biscayne Bay
during the winter months, a time in which manatees that have ranged to
more northerly latitudes during other times of the year, return to south
Florida as ambient water temperatures cool. Water temperatures lower than
approximately 200C appear to increase manatee’s susceptibility to coldrelated stress and cold-induced mortality. In north and central Florida,
manatees’ winter-time distribution is primarily centered around reliable
sources of warm water (e.g., power plant discharges, springs). Other
manatees move south, where it is less likely that ambient water temperatures
will drop below acceptable levels.
Manatees inhabit both freshwater and saltwater habitats, and the USFWS
(1999) reports that: “Several factors contribute to the distribution of manatees
in Florida. These factors are habitat-related and include proximity to warm
water during cold weather, aquatic vegetation unavailability, proximity to
channels of at least 2 m in depth, and location of fresh water sources.”
Natural or artificial sources of freshwater are sought by manatees,
particularly those individuals that spend time in both estuarine and brackish
water.”
Manatees are opportunistic herbivores that feed on a variety of submerged,
emergent and floating plants. Although their most well-known forage
species are seagrasses, including turtle grass, and manatee grass they are also
known to consume algae (Lewis et al. 1983). Although manatees
unquestionably inhabit areas with marine salinities, and appear to survive