RECOVERY OF REGIONALLY HEALTHY POPULATIONS OF ENDANGERED, THREATENED, KEYSTONE AND INDICATOR SPECIES OF ANIMALS
J. Ogden (Chair), South Florida Water Management District
D. Jansen, National Park Service
S. Jewell, Fish and Wildlife Service
C. Johnson, Fish and Wildlife Service
R. Pace, Fish and Wildlife Service
M. Poole, Florida Game and Fresh Water Fish Commission
W. Robertson, National Biological Service, and
M. Steinkamp, Fish and Wildlife Service
The task of this team has been to identify a representative list of native species of animals, which can serve as indicators of the health of regional ecosystems, and which are judged to be important for the contributions that each makes to the character, diversity and personal enjoyment of the natural areas of south Florida. For each species selected, the team has recommended a long-term recovery goal for the population in south Florida, and indices which can be used to measure whether the restoration programs are producing the desired changes or conditions in these populations. Species selected by the team were ones which met all or most of the following criteria: (1) they must be species which we would expect to be responsive to regional, ecosystem restoration programs; (2) we must understand enough of the past and current status (including interannual variability), the biology, and the regional ecology, to be able to interpret the responses of each to restoration programs; (3) they must be species which can be reasonably well monitored over large spatial and temporal scales; and (4) they should be species which are considered by a relatively large part of the human population in Florida to be charismatic or, by some other standard, to have a high profile among human value systems.
The team also placed value in selecting a diverse enough array of species such that, (1) each of the nine ecological subregions in south Florida (Science Sub-Group 1993) would contain one or more of the selected species, (2) the list would include both wetland and upland species, and (3) the list would include representation from the major taxonomic groups (mammals, birds, etc.). Future decisions regarding additions to the list of species should be responsive to these spatial, ecological and taxonomic targets. Because of a lack of information on a large number of plants listed by the Florida Department of Agriculture (Wood 1994), the team has delayed a recommendation regarding the inclusion of plants on this list. Further, we have assumed that the Vegetative Cover team will directly or indirectly address the endangered plant issues.
The list of animals recommended by the team to serve as indices for measuring the success of ecosystem restoration programs in south Florida contains the following endangered, threatened, keystone and indicator species: Florida Panther, West Indian Manatee, Brown Pelican, Wood Stork, Bald Eagle, Osprey, Snail Kite, White-crowned Pigeon, Red-cockaded Woodpecker, Cape Sable Seaside Sparrow, American Alligator, American Crocodile, Green Turtle, Loggerhead Turtle, Tree Snail (Liguus). A separate account for each of these species is attached.
Each species account includes a minimum of four topics: (1) baseline information, (2) recovery goals, (3) measures of success, and (4) research needs. The baseline section presents a brief statement of the relevance of that species to the restoration process, including a description of the status and range (subregions), and the ecological issues which are most closely linked to the species. The recovery goal is a statement of the long-term restoration target for the species, one which more closely mimics pre-project population patterns of the species, and better assures the maintenance of a healthy population over a long time frame. Measures of success include recommendations for the parameters that should be measured, the frequency of measurements, and the rates and directions of change for these parameters which indicate favorable, unfavorable or neutral responses by the species. The recommendations regarding the frequency and desirable rates of change are based on current understandings of expected levels of interannual variability in south Florida populations of the species. The recommendations for the priority research needs are guided by opinions of the team of what information should be obtained (through research and monitoring) to improve the value of the species in question, as an index of the restoration program.
The American Alligator was chosen because it is a keystone species in wetland ecosystems, where its ponds and surrounding mounded vegetation, nest mounds, and trails through otherwise dense marsh vegetation help to shape the landscape, thereby playing a vital role for a wide range of other species. Although have been conducted since the early 1970s to monitor population trends (Woodward & Moore 1990), there have been no systematic investigations into how well the alligator has continued to perform its keystone functions, particularly in systems into which deep-water canals and artificial levees have been introduced (i.e., Water Conservation Areas). The extent to which these structures have altered the habitats of alligators in the natural system is not well understood. Anecdotal information was provided by Craighead (1968), who estimated that there was roughly one alligator pond for every three acres of wetlands peripheral to the deeper sloughs of Everglades National Park before a series of droughts and hydrological alterations caused by the construction of Tamiami Trail may have caused catastrophic declines in the alligator population in the park. He also reported shifts in the population distribution away from the freshwater mangrove zone and peripheral wetlands into Shark River Slough. Since then, Mazzotti and Brandt (1994) have concluded that the alligator is not doing well in the managed marsh systems of the Water Conservation Areas and the park, where pulsed regulatory releases of water frequently cause nest failures, either through desiccation or through inundation of eggs.
The primary recovery target is an increase in the number of alligator ponds occupied by adult alligators. Craighead (1968) has suggested an optimum density of one pond for every three acres of wet prairie habitat in the southern Everglades, but no figures have been proposed for other wetland habitats or other areas of south Florida. To accomplish this, other recovery targets include: (1) a more gradual flooding of wetlands peripheral to Shark River Slough, around tree islands, and within the littoral zone from early June through September; (2) a shift of the population to wetlands flanking sloughs and to the freshwater mangrove zone; (3) a full spectrum of size classes, indicating successful nesting over a period of years; and (4) maintenance of at least eight individuals per mile of shoreline in canals, riverine systems, and lake margins.
Establish areas to be monitored by fixed-wing aircraft, helicopter, or remote sensing on a regular basis for trends in number of ponds, nest mounds, and trails within each area. Because the landscape alterations made by alligators are relatively persistent, monitoring surveys need only be conducted once every five years. Population indices can be derived by night-light surveys according to the protocol recommended by Woodward and Moore (1990).
The American Crocodile (Crocodylus acutus) is listed as endangered by the U.S. Fish and Wildlife Service and the Florida Game and Fresh Water Fish Commission. The crocodile is restricted to the outer mangrove zone on the mainland, and the network of coastal bays and lagoons between Biscayne Bay and Sanibel Island (Subregions 2, 6, 7, and 8). Surveys have revealed an increase in the number of active nesting sites from about 20 during the 1960s, to 45 in the mid-199Os. Crocodiles have expanded the nesting range during this period westward in Florida Bay to include the Flamingo area and the Cape Sable peninsula, and more recently, to the Marco and Sanibel island areas. The only counter trend has been the disappearance of nesting in the lower Florida Keys. The primary constraints on the size and range of this population seem to be habitat loss, highway mortality, raccoon predation at nests, and the possibility that high salinities adversely influence distribution and survival patterns. It has been suggested that crocodiles may benefit from sea level rise (W. Robertson, pers. comm.).
The goal is to recover and maintain a population containing no less than 60 breeding females, and to maintain multiple source subpopulation centers (F. Mazzotti, pers. comm.). Source subpopulations are defined as reproductive centers (north Key Largo, eastern Florida Bay, etc.) from which animals successfully disperse (i.e. survive) to other suitable habitats, including other reproductive centers, in south Florida.
Annual surveys of nests should show continuing increases in the number of nesting females, and a 75 % or better rate of nesting success (nests which hatch young). At five year intervals, tagging and recapture studies in the three primary reproductive centers (Turkey Point cooling canals, north Key Largo, eastern Florida Bay) should be conducted to measure dispersal patterns. At present, only north Key Largo has been demonstrated to be a source subpopulation (F. Mazzotti, pers. comm.). A survey year with increases in both the number of nests and a > 75 % nest success rate will be considered as "improvement"; a year with a decline in the number of nests or a < 75 % nest success rate will be considered as a "stable" year; a year with both a decline in nests and a < 75 % nest success rate will be considered as a year of "deterioration."
Two primary research needs are to, (1) measure relationships between salinity and crocodile distribution, survival (juveniles), and behavioral patterns, and (2) measure dispersal patterns associated with each reproductive center.
Although the southern Bald Eagle (Haliaeetus leucocephalus leucocephalus) is listed as endangered by the U.S. Fish and Wildlife Service, and as threatened by the Florida Game and Fresh Water Fish Commission, nesting subpopulations in some south Florida subregions appear to be healthy. Approximately 70 nesting pairs are currently known in south Florida, in Florida Bay, the lower Florida Keys, the Gulf coast north to Cape Romano, and the Atlantic coast between Biscayne Bay and Sebastian Inlet. We have no current infonnation from several other areas in south Florida where eagles have been known to nest, including the Everglades/Big Cypress ecotone, the coast north of Cape Romano, and the Kissimmee River basin. The fact that the total number of nesting pairs of eagles in central and northern Florida has increased substantially during the past 20 years, while the total in south Florida has not increased, suggests the possibility that conditions for at least some subpopulations in south Florida may be adversely impacted by habitat deterioration.
The goal is to have a regional population of eagles of no less than 100 nesting pairs, with nesting occurring in at least 6 subregions (1, 2, 6, 7, 8, and 9).
Aerial surveys to locate and determine the success of eagle nests in the south Florida subregions should be conducted at three year intervals (or rotate between different subregions during annual surveys). Two measures of success will be based on (1) whether the total, regional nesting population increases, remains stable, or declines between surveys, and (2) whether the number of subregions with nesting eagles increases, remains stable, or declines.
The highest priority is to re-establish nesting surveys in some areas where small numbers of pairs may still occur, for example along the Everglades/Cypress ecotone and the forest fringes along the eastern Everglades. Because these subpopulations are small and far from other nesting eagles, the areas have not been surveyed adequately for several decades. So long as regional nesting populations remain at or near the recovery goal, no other research may be required.
The Brown Pelican (Pelecanus occidentalis) and Osprey (Pandion haliaetus) are listed as Species of Special Concern by the Florida Game and Fresh Water Fish Commission (Osprey for Monroe County only). Both are common predators on f~shes in Florida estuaries (Osprey in inland lakes, rivers and swamps also). During the period when both species have shown significant recovery of nesting populations throughout the Florida peninsula (1960s to present), both have declined in Florida Bay (Subregion 8). Brown Pelicans have declined from 800 + nesting pairs in 6-9 colonies in the Bay during the 1970s, to 300+ pairs in 3 colonies during the 1990s. Kushlan and Frohring (1985) suggested that "ecological deterioration" in the Bay, including a reduction in prey availability, was the most likely explanation for a reduction in nesting pelicans between 1977-1981. Osprey in Florida Bay declined from 190-220 nesting pairs in 1968-1973 (Ogden 1975) to 70 pairs in 1993. Nesting success for active Osprey nests in the Bay was 0.77 to 1.01 fledglings per nest in 1968-1972, and was 0.56 fledglings per nest in 1986-1987. Poole (1982), Kushlan and Bass (1983), and Bowman et al. (1989) have suggest that Ospreys in the Bay have become stressed by food shortages.
For both species, the goal should be to recover and maintain larger nesting populations than currently occur in Florida Bay. For Brown Pelicans, the minims nesting population should be 500 pairs, in 5 + colonies; for Ospreys the minimum population should be 150 pairs.
Brown Pelican nesting colonies and individual Osprey nests can be located and censused by means of a series of aerial surveys each nesting season. Success for pelicans would include increases in the number of nesting pairs and increases in the number of colonies in the Bay. For Osprey, success would be measured by increases in the total number of active nests throughout the Bay, and by increases in production rates (numbers of young fledged per active nest). For both species, an increase in the number of nesting pairs greater than 10% from the preceeding year will be considered as "improvement"; a nesting population within 10% of the preceeding year population will be considered "stable"; a decline greater than 10% will be considered as a year of "deterioration." Each of these three ratings should be weighted relative to whether the year-to-year change is occurring below or above the level of the recovery goal.
The causes for the declines in the Florida Bay nesting populations have not been conclusively determined for either the Brown Pelican or the Osprey. The research and monitoring priorities are to, (1) establish long-term monitoring protocols and programs to measure reproductive paramenters for both species in the Bay (numbers of nesting birds, nesting success), and (2) determine prey dynamics and availability related to the foraging and nesting dynamics of the two species, and to a range of environmental parameters (salinity, turbitity, etc.).
The Cape Sable Seaside Sparrow (Ammodramus maritimus mirablis) is listed as endangered by the U.S. Fish and Wildlife Service and the Florida Game and Fresh Water Fish Commission. This subspecies is restricted to short-hydroperiod prairies in Everglades National Park and the Big Cypress National Preserve (Subregions 6 & 7). Helicopter surveys of the total, known population of Cape Sable Sparrows conducted in 1981, 1992, 1993, and 1995, produced estimates of 6,600 birds, 6,450 birds, 3,347 birds, and 2,624 birds, respectively (Pimm 1995). The decline is thought to have been caused by habitat alterations on the prairies where the birds nest. Water management practices have overdrained prairies east of Shark Slough, which may have been a contributating cause for invasions by woody plant into sparrow marshes, while unnaturally lenthened hydroperiods on prairies west of Shark Slough during high rainfall years may have adversely altered the composition and structure of herbaceous communities in important nesting sites for that subpopulation of sparrows.
The goal is to recover and maintain two core subpopulations of the Cape Sable Sparrow, one on each side of Shark Slough. Each core subpopulation should maintain 2,000 or more birds during years of high water and low water conditions. One or more secondary subpopulations should be present on each side of Shark Slough.
It is not practical to conduct surveys of the total population of Cape Sable Sparrows in all years. Complete surveys should be conducted during two consecutive years, beginning every five years. During each, intervening three year period, hydrological patterns in areas of suitable sparrow habitat should be monitored and evaluated through modeling and attention to hydrological gage data. A survey year with increases in both core populations will be considered as "improvement"; a year with an increase in one core population and a decline in one core population will be considered as "stable"; a year with a decline in both core populations will be considered as a year of "deterioration."
The three top priorities are to, (1) determine mortality rates during a range of water depth and seasonal patterns, (2) determine the patterns of movements and dispersal under a range of water depth, seasonal, and age-class conditions, and (3) determine the influences on nesting effort and success from a range of surface water patterns and fire histories.
Manatees are a wide-ranging species dependent on estuarine and riverine habitats along the Atlantic and Gulf coasts from northern Virginia to Texas. Their decline parallels a system-wide decline in seagrass beds and the development of shorelines, an increase in boating traffic in areas where manatees travel, feed, rest, and give birth, and a reduction in water quality throughout their range. A documented increase and subsequent stabilization in the manatee population would seem to indicate that system-wide expanses of healthy seagrass beds were once again available, that waterways were adequately protected from undue disturbances, that water quality had improved, and that estuaries and riverine habitats throughout the southeastern US had regained a high level of productivity.
Historical accounts and archeological evidence of manatees prior to the first half of the 20th century are poor and often contradictory. Anecdotal reports that the population was in trouble in the late 1 800's led to the elimination of hunting in 1893. Since then, particularly since the manatee was listed in 1967, the amount of information has steadily increased, although it is still impossible to do more than roughly estimate the size of the population.
Synoptic surveys for the last several years have yielded minimum population counts. Regular aerial surveys have yielded trends in the seasonal use of warm- water refuges. The percentage of calves observed each year during aerial surveys has been used to infer the annual reproductive rate. The age-at-death of recovered carcasses as well as their sex and reproductive status has been used to estimate the population's reproductive rate and understand age-related survivorship. Telemetry studies have allowed scientists to map manatee migration routes and determine the extent and variability of their range. Mark-resight analyses of manatees with unique scar patterns have further explained their behaviors.
Downlisting from "endangered" to "threatened" will be considered when best available scientific data indicate that the population is growing or stable, when mortality factors are controlled at acceptable levels or are stable or decreasing, and when critical habitats are secure and threats to them are controlled or decreasing. The long-range recovery goal is to restore the Florida manatee population to its optimum sustainable level.
In addition to the methods mentioned above, recent breakthroughs in age determination will improve understanding of population structure. New efforts by population biologists will refine the definition of 'Recovery Goals' and make the identification of trends in abundance more easy to recognize.
Subregional breakdown: There is little known mixing of manatees on the Atlantic and Gulf Coasts, yet genetic interchange does occur because they are genetically indistinguishable. Within these two herds, manatees tend to group themselves loosely by often returning to the same warm-water refuges each winter and by tracing similar warm weather migratory routes. These groups constitute useful management units but recovery methods are the same for the entire population: 1) seasonal protection of over-wintering spots and adjacent seagrass beds and other feeding grounds with constant monitoring to ensure compliance, adequate water quality, and aufficient food supplies, 2) seasonal protection of migration corridors to allow manatees safe passage to and from warm-water refuges, 3) seasonal boat speed zones in critical coastal counties of Florida and southern Georgia during spring, summer, and fall, wherever and whenever studies show manatees are common, and 4) regulating shoreline developments in manatee habitat to take into account alteration of habitat and manatee safety.
Research needs are described in the 1996 Second Revision ofthe Florida Manatee Recovery Plan. It recommends continuing and expanding research efforts that will enable the Service to better identify and minimize causes of manatee disturbance, injury and mortality, to protect essential manatee habitat, to determine the status of the population, and to monitor and evaluate recovery progress.
The Florida Panther (Felis concolor coryi) is listed as endangered by the U.S. Fish and Wildlife Service and the Florida Game and Fresh Water Fish Commission. The only remaining wild population, an estimated 30 to 50 adults, survives within the bounds of Subregions 2, 6, and 7. The presence of the panther is indicative of large expanses of contiguous wilderness that supports healthy populations of large prey such as deer, wild hogs, and alligators. Low numbers of panthers and habitat fragmentation have resulted in inbreeding, manifested by loss of genetic variability and a reduction in overall fitness. Panther viability projections have concluded that, under current conditions, the free-ranging Florida panther population will likely become extinct in two to four decades.
The overall recovery goal for the Florida panther is the establishment of a minimum of three viable populations within the historic range of the subspecies. One of these populations should occur in southern Florida.
In order to establish the panthers in south Florida as a viable population, the following objectives should be achieved: (1) No loss of existing, currently-used habitat; (2) Expansion of panthers into other areas of suitable habitat, and public acquisition of these areas as needed; (3) Utalization of wildlife underpasses throughout panther habitat; (4) An increase in the percentage of kittens that survive and are recruited into the adult population; (5) A substantial reduction in the percentage of panther deaths caused by vehicles along highways (currently 49% of total mortalities); (6) Reduced level of mercury contamination in wild panthers; (7) Improvements in genetic heterozygosity (including documentation of cross-breeding with Texas cougars), and a substantial reduction in the occurrence of cryptorchism.
Continue the capture and radio-collaring of all known panthers, to improve the understandings of habitat utalization under a range of conditions, and to monitor the health of animals in the wild population.
The Florida tree snail indicates the geographic extent and ecological condition of hardwood hammocks along the extreme southern coasts, the southern Everglades, Big Cypress, and the Florida Keys. In addition to loss of hammocks from urban development, abundance of Florida tree snails is affected by aerial mosquito spraying (Florida Keys), fire management, and to a lesser degree by water management (Big Cypress, Everglades). Periodic fire is needed to set back succession and keep the hammocks from becoming too dense; however, extremely hot fires that burn the soil can eliminate a hammock that served as Liguus habitat. High snail abundance would indicate a productive hardwood hammock ecosystem in general. The index would consider the species as a whole and would not distinguish among the various color forms of the species; this issue could be addressed separately. The emphasis of previous investigations has concentrated on the distribution of rare color forms; limited anecdotal evidence is available on relative abundance and general distribution of the species. To use Liguus as an indicator, census plots need to be established throughout the range of the species and a baseline would be established. Censuses must use the same technique within each subregion and should occur at the same time of year.
No official recovery goal has been established. It is impractical to establish a numerical population goal for an invertebrate that is widespread and locally numerous. A generalized goal would be to increase snail density at selected reference sites and to avoid further reduction in the range of the species.
Census plots would be established at about 10 sites in each of the subregions specified below. Census methodology would be standardized and occur annually at about the same time each year during the wet season. Remote sensing of ha~nmocks would determine if habitat is being eliminated outside of the census plots. Census plots would be established in each of the following sub-regions: Florida Keys, Atlantic coast (Fort Lauderdale to Homestead), Gulf Coast (Marco Island through Ten Thousand Islands), Big Cypress, and Everglades. Loss of hardwood hammock habitat would also be estimated by remote sensing for each of the subregions.
Research is needed on the effect of fire history on the abundance of tree snails. Everglades National Park has fire history data that may be useful. Snail fecundity and diet may be parameters that can be correlated with fire history if snail abundance is not conclusive.
Immature green sea turtles would provide a measure of the quality of the near shore and estuarine ecosystems. Immature green sea turtles leave the pelagic habitat when they reach a carapace length of approximately 20-25 centimeters and enter benthic feeding grounds. Most often, these foraging habitats are pastures of sea grasses and/or algae, but small green turtles can also be found over coral reefs and rocky bottoms. In south Florida, the Indian River Lagoon, Florida Keys and Florida Bay have been identified as important foraging grounds for green sea turtles. The loss or reduction in quality of these habitats impact green sea turtle populations by removing important developmental habitat. Additionally, environmental stresses within these habitats such as contaminants, appear to have lowered the immune system function of green sea turtles. In recent years there have been increased numbers exhibiting infection with fibropapillomatosis.
Populations of immature green sea turtles in the developmental habitats of the Indian River Lagoon and Florida Bay have been studied since 1982. Since 1989, aggregation studies of juvenile green turtles dwelling over the near shore worm-rock reefs have been conducted in northern Indian River County. While both loggerhead and green sea turtles utilize these systems, preliminary monitoring techniques have shown green sea turtles to provide a greater catch per unit effort and therefore, should be better indicators. From 1979 to date, abundance data are available from the capture of sea turtles at the St. Lucie Power Plant. Some baseline information is available for the incidence of fibropapillomatosis in green sea turtles in south Florida and researchers are ready to develop diagnostic tests for monitoring the presence of this disease in green turtles.
To consider the species recovered in south Florida the following criteria must be met over a period of 25 years:
A uniform method to index the abundance of immature sea turtles in foraging habitats needs to be developed. Once developed, annual monitoring of immatures within the Indian River Lagoon and Florida Bay should be conducted. No differences exist at the subregional level for this species.
Additional research is necessary to determine the cause of the recent increase in incidence of fibropapillomatosis in green sea turtles. Several field studies have suggested that high incidence of fibropapillomatosis is associated with environmental cofactors (contaminants) in the near shore areas of south Florida. Diagnostic tests for monitoring the prevalence of this disease in populations of green turtles (and other affected turtles) need to be developed. A uniform method to index the abundance of sea turtles within foraging habitats needs to be developed to monitor the prevalence of the disease.
The loggerhead sea turtle would provide a measure of the quality of south Florida's nesting beaches, including the effectiveness of the regulatory process with regard to anthropogenic impacts. Sea turtle nesting success is highly dependent on the quality of nesting beaches, with numerous characteristics influencing beach quality. If beaches are badly eroded or the quality of the sand is low as a result of beach nourishment, nesting success will be poor. If lighting is not regulated during the nesting season, hatchling mortality will be high and nesting attempts by females may be reduced. If compaction of the sand has occurred due to beach nourishment or if a seawall has been constructed, nesting effort may be reduced. Loggerhead sea turtles nest in higher density in south Florida than all other species of sea turtles and therefore, would be the best indicators of nesting beach quality. Baseline data are available for loggerhead nesting effort on a large number of important nesting beaches in south Florida. In 1989, a standardized program, the Florida Index Nesting Beach Survey Program, was developed and implemented for Florida's important nesting beaches. Since this time, standardized annual nest surveys have been completed for the Loggerhead (in addition to all other sea turtles nesting in Florida) on index beaches. The information collected from these surveys can be used to statistically and scientifically analyze population trends and distribution.
The 1993 Loggerhead Turtle Recovery Plan identifies criteria necessary to recover the species. The adult female loggerhead population must be increasing over a period of 25 years. Twenty- five percent of all available nesting beaches must be in pubic ownership and be distributed over the entire nesting range and encompass at least 50 percent of the nesting activity within south Florida. Recovery Goals are similar for all south Florida beaches.
The Florida Index Nesting Beach Survey Program should be continued to provide a measure of long term trends in loggerhead turtle population size and distribution and therefore, a measure of the quality of south Florida's beaches over time. Any beaches within south Florida not originally identified, and deemed important to measure south Florida ecosystem restoration, should be added as index beaches.
Presently, there is limited information on the habitat needs of immature loggerheads. Increased effort is necessary to determine what habitats are critical for immatures. An effective method for monitoring immatures needs to be developed and implemented. Once developed, abundance data could be collected and habitats important to immatures could be identified and protected.
The Red-cockaded Woodpecker (Picoides borealis) is an obligate, nor~migratory resident in extensive stands of mature, southern pinelands. It is listed as endangered by the U.S. Fish and Wildlife Service, and as threatened by the Florida Game and Fresh Water Fish Commission. Based on a recent count of 111 occupied sites in the southern peninsula, this "population" is estimated to contain 255 woodpeckers, including 94 mated pairs. The population in and adjacent to the Big Cypress National Preserve is ranked as the 15th largest in the 13 states where the species occurs. Habitat within this southwestern Florida population was damaged by Hurricane Andrew and the prolonged high water period, 1993-1995. A stable population of Red-cockaded Woodpeckers is indicative of the existence of a functional pineland ecosystem.
Although the range-wide goal of maintaining regional populations of 250 mated pairs is not feasible in south Florida, a target of not less than 100 pairs is achievable.
The maintenance of all known cluster populations (discrete groups of occupied sites) will be considered as a measure of a stable population in south Florida. An increasing population can be achieved by means of more active habitat management in unoccupied pinelands (prescribed fire, cavity provisioning, species reintroductions), and by land acquisition in order to preserve the integrity of suitable pinelands and to protect or create habitat corridors. Reintroduction of woodpeckers into the Long Pine Key, Everglades National Park, will be considered as one measure of success.
The immediate need is for a comprehensive survey of all potential pinelands, public and private, to determine the amount of suitable nesting and foraging habitat, and number of active woodpecker clusters in south Florida. Criteria for habitat suitability include 200 to 400 acres of pine forest, with potential nesting trees a minimum of 60 years old and having a basal area between 60 and 90 sq. feet per acre. A "Habitat Conservation Plan" for the woodpecker in south Florida is required.
The snail kite would provide a measure of water conditions throughout the Kissimmee- Okeechobee-Everglades watershed. This highly migratory and opportunistic species responds rapidly to water management actions and can indicate the spatial extent of suitable habitat and the degree of flexibility in the system The number and distribution of optional habitats under various water conditions will provide an index of the system's flexibility not only for the snail kite, but most likely for other species. Baseline data are available, but there is some concern about bias in the data. A yearly mid-winter snail kite census had been conducted continuously from 1969 through 1994. Although these likely did not account for all the snail kites, it did represent a high percentage of the population. The FGFWFC proposes to resume this census every other year. Rob Bennetts proposes that the annual census be substituted by a mark-and-relight program to estimate total population. Summer nesting surveys are available from 1986 to 1995; in addition to the number of nests, detailed data often include nesting substrate, water depth, and nesting success rate.
The 1986 Recovery Plan set an interim population goal as an annual average of 650 birds over a seven-year period, with annual declines that do not exceed 10 percent of the seven- year average. This goal will be reviewed this year during the FWS' multi-species recovery plan. It may be unrealistic to impose a 10 percent limitation on annual decline for any given year for a species that naturally experiences great fluctuations in population. Stability or increase of the population over a long-term period (7 to 10 years), combined with a goal for spatial distribution of habitat, would probably be more appropriate. Recent work by Rob Bennetts suggests that a mark-and-relight method be used to statistically estimate population rather than the traditional mid-winter census.
Natural year-to-year variability (such as meteorologic variation) should be expected to mask any human-caused effects (such as restoration projects), so it seems appropriate to keep a multi-year running average as an index. A period of at least 10 years would be needed to average out variability in weather patterns. Given the opportunistic nature of the snail kite to seek suitable habitat, year-to-year stability in the location of nesting and prime feeding areas is not a realistic goal. The mark-and-relight data should be reported for three subregions within the South Florida ecosystem--Kissimmee, Lake Okeechobee, and the Water Conservation Areas; and for one site outside the watershed--the Upper St. Johns marsh. Snail kites readily migrate among these areas.
Refinement and implementation of mark-and-relight technique for population estimate is needed.
White-crowned pigeons are strongly associated with the vegetative diversity of tropical hardwood hammocks, and the pigeon's reproductive success is partly dependent on the availability and geographic location of larger, less fragmented habitats. The pigeon plays an important role in maintaining the diversity of the hammock ecosystem by eating the fleshy fruits and dispersing the seeds, while flying between hammocks. In turn, dispersion of the seeds leads to greater species diversity in the hammocks, ensuring the availability of fruit-bearing plants through a longer portion of the year. The resulting higher diversity of plants sustains a more diverse assemblage of animals in the hammocks. National Audubon Society (NAS) research demonstrates that within a few days of fledging from Florida Bay mangrove islands, young pigeons seek shelter in Florida Keys hammocks larger than a minimum 12 acre patch size. Continued fragmentation of the remaining hammocks will reduce successful recruitment of young birds into the population and increases the vulnerability of young and mature pigeons to predation. The distance between the larger hammock patches influences the successful dispersion of pigeons (and most likely other species, such as the mangrove cuckoo, yellow-billed cuckoo, white-eyed vireo, and northern flicker). The NAS has conducted a number of studies on the white-crowned pigeon. A standardized counting methodology was used in 1991, obtaining a thorough population estimate for the area east of a line running from Long Key to Cape Sable (does not include the Lower Keys). Boat-based counts have been conducted at particular nesting/roosting islands, particularly at Middle Butternut Key and Cowpens Key. Road-based surveys were conducted between 1986 and 1991, using the USFWS' Breeding Bird Survey technique. Only one subregion is involved (Florida Keys). Pigeons move between hammocks on the mainland (Everglades National Park) and the Florida Keys.
No recovery target has been established; this should be a high priority task.
The most practical approach to regular monitoring to establish population trends is the road-based Breeding Bird Survey technique. At a minimum, two surveys should be conducted per year -- one in January for the wintering population (currently estimated at 10% of the population peak in the breeding season), and one in June or July during the breeding peak. Existing data include the Middle and Upper Keys; survey routes need to cover the Lower Keys. A more thorough survey of the population should be conducted every 5 to 10 years.
The biology of the white-crowned pigeon is well understood. Research is needed on the effect of hydrologic changes on mangrove habitat structure in Florida Bay and how this may affect pigeon breeding.
Wood storks would provide a measure of the performance of south Florida's wetland ecosystems, including the mainland estuaries. Prior to the 1920's, wood storks in south Florida formed colonies between November and January (December in most years) regardless of annual rainfall and water level conditions (Ogden 1994). In response to deteriorating habitat conditions, wood storks in south Florida have delayed the initiation of nesting to February or March in most years since the 1970's. This shift in the timing of nesting is associated with increased frequencies of nest failures and colony abandonment over the past 20 years. Colonies that start after January in south Florida risk having young in the nests when May-June rains flood marshes and disperse fish. Water management practices that would result in an increase in productivity in the southern mainland estuaries, in addition to a natural cycle of drying in the interior marshes would most likely benefit the wood stork. Recovery of the wood stork would indicate a return to conditions more closely approximating those of the pre-drainage system. Baseline information is available for nesting effort for select colonies in south Florida but, to date, there are no regular colony surveys conducted for Big Cypress, Florida Bay, the Gulf coast of Everglades National Park, or Lake Okeechobee. Additionally, no standardized protocol has been implemented for conducting colony surveys.
Several criteria must be met to consider the wood stork recovered within south Florida:
The spatial extent of colony surveys should be increased to include the Big Cypress National Preserve, Florida Bay, the Gulf coast of Everglades National Park, and Lake Okeechobee. Standardized survey protocol must be developed and implemented for all colony surveys. A shift back to historical nesting patterns may result in a reduction in the number of nests within the central and northern Everglades and Lake Okeechobee when compared to recent years. If the total numbers of nesting pairs of wood storks are stable or increasing in south Florida (due to an increase in the number of nesting pairs within the mainland estuaries and/or headwaters ecotone), a reduction in the number of nests within the interior colonies should not be viewed as detrimental.
While the above efforts will yield information on nesting effort, they will miss an important stage in wood stork development. To monitor wood stork reproductive success, young must be monitored when they are beginning to forage independently. Future monitoring efforts should include efforts to determine post-fledgling success and recruitment into the breeding population. Fledglings from selected colonies should be fitted with radio transmitters and anodized colored leg bands, and followed to determine important foraging locations, and survival.