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T TECHNICAL MEMORANDUM
FROM: William M. Helfferich//j4'17q$
SUBJECT: Biological Justification--Isolated Wetlands Rule
DATE: 6 November 1986
Under legislative mandate, the water management districts were required to
develop rules regarding impacts to fish and wildlife in isolated wetlands,
including a review threshold based on hydrologic and biological evidence.
Public comments on the value of isolated wetlands have been received at the
various public workshops and by letter. The biological community generally
acknowledges the fish and wildlife value of small isolated wetlands.
Isolated wetlands have high fish and wildlife values, particularly as foraging
areas for wading birds. In addition, they provide necessary breeding habitat
for amphibians. These scattered wetlands are critical as emergency foraging
areas during times of high water when food organisms are dispersed in larger
marshes. Based on the oral and written comments, current fish and wildlife
values cannot be expected to be maintained if the protection of small isolated
wetlands and their functions are not also maintained.
The State Comprehensive Plan, Chapter 187, F.S., and the State Land Development
Plan state as goals to "protect and acquire unique natural habitats and
ecological systems, such as wetlands...and restore degraded natural systems to a
functional condition," and as policies to "conserve forests, wetlands, fish,
marinelife and wildlife to maintain their environmental, economic, aesthetic and
recreational values", and "protect and restore ecological functions of wetland
systems to insure their long term environmental, economic and recreational
Numerous studies have been published documenting the importance of isolated
wetlands for wading birds. Between 1938 and 1981, Walkinshaw (1981), studied
sandhill crane nests in central Florida. Of 137 nests observed, 81 were in
ponds less than 10 acres in size. Emergent marshes, dominated by pickerelweed
and maidencane contained 124 of the 137 nests, and 99% of the nests were found
in shallow standing water (mean depth--12"). Nesting pond sizes ranged from 0.5
acres to 120 acres. The study indicated that during wet years, sandhill cranes
select smaller ponds than normal for nesting. Walkinshaw (1976) further cites
the adaptability of sandhill cranes to live and breed in association with
development activities. He reports a pair of cranes have been nesting for seven
*- years on a pond covered with emergent vegetation on the Lake Placid Golf course.
"The pair, with chicks, passes golfers daily, neither paying much attention to
November 6, 1986
Beissenger and Takekawa (1983) report on the use of isolated wetlands by snail
kites during drought conditions. In 1981 and 1982 kites, whose primary diet
consists of apple snails, dispersed throughout peninsular Florida in search of
foraging habitats. Most habitats used by kites during the drought were quite
different from typical Everglades or lake marshes that kites use during wetter
periods. Kites were most frequently observed along urban, roadside or _
agricultural canals. The east coast corridor supported many scattered small
groups of kites. Small permanent and seasonal wetlands also were used
frequently. Although much of the natural.habitat along the east coast has been
developed and drained, it has the highest rainfall in south Florida and kites
might expect to find some wet areas here when most others are dry. Kites were
willing to move great distances and use very small patches of sub-optimal
habitat to survive dry periods. "Seasonal marshes are important for kite
survival during Florida's cyclic droughts and need to be preserved to insure
survival during these periods."
Kushlan (1981a) discusses white ibis foraging in south Florida. White ibis
forage in different parts of south Florida at different times of the year. In
summer, ibis move to coastal habitats and later, by a series of shifts,
throughout the interior of the Florida peninsula. Segments of their population
thereby successively occupy newly suitable foraging areas and use most of the
available habitat of southern Florida during the course of a year. The
sequential availability of such productive habitats over the year allows the
marshes and swamps of the southern Florida wetlands to support relatively large
populations of both wintering and resident wading birds. Kushlan (1975) further
discusses the movements that other species of birds make in conjunction with
fluctuating water levels. The shifts of the wood stork correspond to changing
availability of forage species, but differ in timing and sequence from those of
the white ibis. Unlike the ibis, the wood stork, due to its different feeding
technique, is not completely dependent on falling water levels to concentrate
food organisms, but rather on having water sufficiently shallow to make foraging
possible. Herons and other marsh birds apparently also move seasonally
throughout south Florida.
Kushlan (1977) describes that after completing nesting, wading birds tend to
disperse northward into temperate marshes, where food may be approaching its
seasonal maximum. As a result, the annual resource base available to the
population is increased. As wood storks return to south Florida in the Fall,
they forage initially in coastal marshes and then begin intraregional movements,
moving through a succession of coastal and inland foraging sites throughout the
nesting period. These movements correspond with the timing of seasonal drying
of various marshes.and resulting concentration of fish on which the storks
depend (Ogden, et al. 1976). Aggregated foraging permits efficient use of the
ephemeral ponds that characterize many wading bird habitats. The amount and
distribution of resources and their availability change markedly on a daily or
seasonal basis such that wading birds may be able to feed on these resources for
only relatively short periods at a time. By aggregating, birds find and use
these locations as they become available. In south Florida, seasonal changes in
forage species availability cause aggregations to form daily at newly suitable
sites and, as a result, the birds sequentially use more of the habitat
available over the annual drying cycle. When resource status changes
November 6, 1986
gradually, patches may be sampled sequentially as they become available. As
south Florida swamps dry seasonally, birds can use one patch until it is
depleted and then move to a nearby patch where prey may become available later
The South Florida Water Management District, Everglades National Park and
Florida Game and Freshwater Fish Commission are cooperating in a standardized
bird survey of the Water Conservation Areas, Everglades National Park and Big
Cypress Preserve. This is referred to as the Systematic Reconnaissance Flight
(SRF) program. This program allows the three agencies to count birds on a
monthly basis, plot their location within these reserve areas and keep track of
the wetted ground surface. The data shows bird numbers increasing slowly from
December 1985 through March 1986, as the slow drying process concentrates food
organisms in these large marshes. Excessive rains during late March increased
stages throughout most of the survey area. The rising water levels resulted in
the disappearance of 116,000 birds from the survey. The agencies have no way of
tracking the birds after they leave the respective areas, but it is believed
that they were utilizing the thousands of scattered isolated wetlands (Dineen,
In a 9/30/86 letter submitted to the District, Mr. Fred A. Johnson, Waterfowl
Program Coordinator of the Florida Game and Freshwater Fish Commission,
discusses mottled ducks and isolated wetlands. "After three years of
( experimental surveys we now know that the prairies of south-central Florida
comprise the heart of the mottled duck's range. These grassland prairies are
primarily associated with the watersheds of Fisheating Creek and the Kissimmee
and St. Johns Rivers. The bulk of our mottled duck observations on these
prairies have not been associated with the larger lake marshes, but with the
thousands of small, seasonally inundated ponds that dot the landscape. These
wetlands and adjacent grasslands are especially important during the breeding
season (March-June) for nesting and brood-rearing."
A similar letter, dated 10/13/86, was submitted by Ms. Mary Anne Bishop, project
biologist with the Department of Wildlife and Range Sciences at the University
of Florida, studying sandhill cranes. "I wanted to call to your attention the
importance of wetlands that are smaller than five acres. We have found that
these smaller wetlands are used frequently by the Florida sandhill cranes for
nesting. In 1986, we identified 103 wetlands with sandhill crane nests on the
Kissimmee Prairie. Of the 103 nests, some 28 (27%) were in wetlands smaller
than five acres. Additionally, our field work on radio-banded and marked cranes
on the Kissimmee Prairie has found that pairs and families tend to stay in the
vicinity of the nest marsh throughout the year. After the chicks hatch, the
nest marsh is used extensively for brooding. And, both the nest marsh and other
nearby wetlands (often smaller than 5 acres) are used throughout the year for
foraging and roosting."
All of the literature cited to this point has dealt with larger animals--
primarily wading birds. Mr. Paul E. Moler, biological scientist with the
(/ Florida Game and Freshwater Fish Commission's Wildlife Research Laboratory in
Gainesville, raises some very pertinent points concerning other wildlife
utilization of small isolated wetlands. Mr. Moler's letter deals with the
November 6, 1986
breeding requirements of a number of amphibians--toads, frogs, and salamanders.
The major importance of the amphibians is the role they play as food source to
other wildlife. Amphibians are a cornerstone of the vertebrate food chain.
Herons and egrets restrict their diets largely to fish, but sandhill cranes and
indigo snakes, both threatened species, routinely eat frogs and toads. Several
other species of non-poisonous snakes, including garter, ribbon, banded water
and gopher snakes feed heavily on frogs and toads. Mr. Moler sites a number of
amphibians which utilize only the small wetlands; they are not found in larger
systems. Gopher frogs will travel as much as two miles to reach a breeding
pond. A two mile radius drawn around an isolated pond encompasses 8000 acres of
upland habitat. The area utilized by other species vary as a function of the
mobility of the particular species. "To some extent, the biological importance
of isolated wetlands is directly proportional to their degree of isolation. If
there are alternative breeding sites nearby, the loss of a small pond may have
little or no impact on local amphibian populations; whereas, if the degree of
isolation is high (there are no suitable, alternative breeding sites), local
amphibian populations may be totally extirpated."
Two journal articles have been submitted to the District by the public for
consideration in establishing the size thresholds which have been proposed in
the draft rule. The two articles submitted are: "Implications of Marsh Size
and Isolation for Marsh Bird Management," Mike Brown (1986), and "Determining
Minimum Population Sizes for Birds and Mammals," J. Michael Reed (1986).
The Marsh Bird Management article discusses Iowa marshes, which are considerably
different than the wetlands of south Florida. The study deals with marshes
which have been drained since settlement. According to the Iowa Natural
Heritage Foundation, more than 4 million acres of wetlands existed in Iowa prior
to 1875. Today, less than 27,000 acres remain. Most of the original and
remaining wetlands are prairie potholes. The major point of the study deals
with species which nest and breed in the marshes, not those which utilize them
primarily as feeding areas. The study states that "the largest sites were not
the richest in species. The three richest sites were considerably smaller than
the three largest sites." The area-dependent species studied included teal,
mallard and ruddy ducks; swamp sparrow; pied-billed grebe; black tern; and
Canada goose. The report goes on to state that marshes in the 50-75 acre range
were more efficient in preserving bird species than larger marshes (up to 450
acres). "Whereas one large marsh may be less expensive to manage, a refuge
consisting of a cluster of smaller marshes increases habitat heterogeneity and
lessens the risk of disease or problems caused by introductions." A primary
concern of the District is protection of seasonally important foraging areas,
whereas the Iowa study focuses on managing wildlife on large refuges. The
article provides little or no relavent information for establishing minimum
wetland size thresholds in central and south Florida.
Reed (1986) discusses the minimum viable population sizes necessary to maintain
breeding populations of a size which will not be affected by inbreeding. The
examples used were the elk and northern goshawks. In the conclusion section,
the authors state that minimum population sizes for short term and long term
species survival are 50 and 500 individuals, respectively. The District's
concern in wetlands extends beyond population size necessary to prevent
,,ember 6, 1986
In-breeding. Equally important are threatened and endangered species habitat
protection, maintenance of seasonal feeding areas and protection of emergency
foraging sites which are essential during periods of high water. The
maintenance of diverse habitats is the key to conservation and management of
wildlife. "Therefore, in any action plan for wading bird conservation and
management, the focus must be on habitats, not only in the breeding areas but in
the feeding areas. A species' breeding sites cannot be considered in isolation
from its feeding areas" (Curry-Lindahl, 1978).
. 1:.1 .." v". V
,ember 6, 1986
Beissinger, Steven R. and J.E. Takekawa 1983. Habitat use by and dispersal of
snail kites in Florida during drought conditions.
Florida Field Naturalist 11:89-106.
Bishop, Mary Anne, Letter to Richard A. Rogers, SFWMD, 13 October 1986.
PBrown, Mike and J.J. Dinsmore 1986. Implications of marsh size and isolation
for marsh bird management. Journal of Wildlife Management 50(3):392-397.
Curry-Lindahl, Kai 1978. Conservation and management problems of wading birds
and their habitats: a global overview. Wading Birds, Research Report #7 of the
National Audubon Society.
Dineen, J. Walter, Wading bird population estimates for the SRF survey areas
June 1985-June 1986, Unpublished data, SFWMD, 1986.
Florida State Comprehensive Plan, Chapter 187, Florida Statutes, 1985.
Florida State Land Development Plan 1986-2000, Fla. Dept of Community Affairs,
( Johnson, Fred A., Letter to Terrie Miller, SFWMD, 30 September 1986.
Kushlan, James A., J.C. Ogden and A.L. Higer 1975. Relation of water level and
fish availability to wood stork reproduction in the southern Everglades,
Florida. Open-file Report, U.S.G.S., Tallahassee, Florida.
Kushlan, James A. 1977. Foraging behavior of the white ibis.
Wilson Bulletin 89:342-345.
Kushlan, -James A. 1981a. Feeding ecology and prey selection in.the white ibis.
Kushlan, James A. 1981b. Resource use strategies of wading birds.
Wilson Bulletin 93(2):145-163.
Moler, Paul E., Letter to Judith C. Hancock, Florida Chapter--Sierra Club,
16 September 1986.
Ogden J.C., J.A. Kushlan and J.J. Tilmant 1976. Prey selectivity by the wood
stork. Condor 78:324-330.
TReed, J. Michael, P.D. Doerr and J.R. Walters 1986. Determining minimum
Y population sizes for birds and mammals. Wildlife Society Bulletin 14:255-261.
Walkinshaw, Lawrence H. 1976. Sandhill cranes on and near the Kissimmee
f' Prairie, Florida. Pages 1-18 in J.C. Lewis,ed. Proceedings, international Crane
Workshop. Oklahoma State University Pub. and Print Serv., Stillwater.
Walkinshaw, Lawrence H. 1981. Nesting of the Florida sandhill crane in central
Florida. Pages 53-62. Proceedings 1982 Crane Workshop.