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projects > monitoring of wading bird reproduction in Water Conservation Areas and study of survival and movements of juvenile wood storks > scope of work

Project Scope of Work

Project Scope of Work 2003

Monitoring of Wading Bird Reproduction in Water Conservation Areas 1, 2, and 3 of the Everglades, and Study of Survival and Movements of Juvenile Wood Storks


The work is to monitor responses of breeding wading birds to hydrological conditions in the water conservation areas of the Everglades, and to initiate a project designed to reduce uncertainty in predicting population responses of endangered Wood Storks to restoration activities. Monitoring of wood storks was recommended by the USFWS as part of their Biological Opinion on the Interim Operating Plan for protection of the Cape Sable seaside sparrow.

Wood Storks (Mycteria americana) are of special interest with regard to the restoration of the South Florida Ecosystem, both because wetlands of south Florida are considered prime habitat for this federally endangered species, and because the storks' reproductive responses are thought to be an indicator of several aspects of normal ecosystem function. Although considerable reproductive information exists (e.g. fecundity, long term record of nesting numbers, behavior, reproductive parameters) there is almost no information about juvenile or adult survival. The lack of this information means that it is impossible to construct justifiable demographic models for this species. This lack also means that it is impossible to calculate the level or periodicity of reproduction needed to maintain a stable population, or to predict population responses to habitat loss or improvement. In addition, genetic information indicates that storks nesting in south Florida are simply a fluid subset of the larger southeastern U.S. population, yet the movements of these birds, and the specific habitats used are poorly known. The importance of wetlands outside the Everglades, to storks nesting inside the Everglades is a key uncertainty in predicting responses of storks to south Florida restoration.

It is important to fill the gaps in information by studying the survival and movements of storks using satellite telemetry. Satellite tags allow remote tracking of animals anywhere on the globe, without costly and logistically difficult ground or aerial surveys. The recent development of solar powered tags also allows monitoring of survival for indefinite periods (not limited to battery life). Thirty fledgling storks will be fitted with backpack mounted satellite transmitters, and their movements and survival will be documented. Satellite tags will be collected from dead birds for refurbishing and later use. The resulting information will be used in several ways: 1) the development of a basic demographic response model, incorporating existing fecundity, life history, and survival information; 2) a summary of the wetlands frequented by birds in various parts of the year and stages of life; 3) an interactive web site, showing up to date movements of the birds which will be actively marketed to educational institutions (K - college) with the Corps part of the website.


The numbers of breeding pairs of wading birds in the Everglades, and their reproductive success measures have been used for some time to reflect hydrological and biotic conditions in the Everglades, and there is compelling evidence that various aspects of wading bird reproduction and foraging ecology can be mechanistically linked with various aspects of the ecology of wetlands, at a variety of scales. While some of these linkages are simple enough to be revealed by short-term studies, a full understanding of the interplay of many variables (e.g. hydrology, weather, vegetation, prey and fire cycles) is only possible through the use of long term records. Thus while the monitoring of wading birds has been a powerful tool in unraveling the ecology of the birds and the ecosystem, there are excellent reasons for continuing to monitor them. First, the long-term nature of the record of nesting is a powerful context for comparison of any future years. Second, the long term record becomes more powerful with each passing year, particularly for the analysis of the importance of rare combinations of events. Third, a key prediction of the restoration program is that hydrological restoration will result in increased populations of wading birds, earlier nesting for some species, and increased nesting success for some species. Wading bird nesting is therefore a key criterion of restoration, and aspects of their reproductive ecology (energetics, timing, productivity) have the potential for fine-tuning the way that the hydrology of the Everglades is managed. For these reasons, continued monitoring of the Everglades breeding populations is likely to provide crucial information, both for evaluating the progress of restoration, and for fine-tuning our understanding of the underlying ecological relationships between the aquatic ecology of the marsh and the birds.

The Wood Stork (Mycteria americana) is the only stork breeding in the United States, and is a federally endangered species. Wood Storks have special relevance for the restoration of the south Florida ecosystem (encompassing the Kissimmee basin, Lake Okeechobee, the Everglades, Big Cypress, wetlands of southwest Florida, and Florida Bay). Historically, this area was the core reproductive habitat for the species, to the extent that over 75% of the U.S. population was thought to breed in this area (Coulter et al. 1999). The breeding population in the Everglades has declined by over 80% since the 1930s and by at least 50% since the 1960s. In addition, storks have shifted the timing of nesting in the Everglades from November/December initiations, to February/March initiations (Ogden 1994). This shift in timing has meant that storks are usually rear young during the onset of summer rains, when surface water levels rise, prey disperse, and young storks typically starve. In addition, storks have shown marked shifts in the location of nesting, having moved gradually from almost entirely coastal nesting in the Everglades, to inland nesting, as a result of gross dewatering of the coastal regions of the Everglades (Ogden 1994). Storks also began nesting in more northerly locations in north and central Florida, Georgia, and South Carolina during the period 1970 - 2000. These dramatic changes in the characteristics of birds nesting in south Florida has been related to radically altered distribution and timing of surface water in the Everglades (Ogden 1994), as well as an approximately 50% loss of wetlands in Florida since Europeans arrived (Tiner 1984). Thus the restoration of south Florida wetlands seems to be extremely important to the restoration of breeding Wood Storks to the area.

The restoration of storks may also be a signal of successful restoration of key hydrological and biological functions of the south Florida ecosystem (Ogden 1994). By virtue of their unique grope-foraging technique, storks seem to require very dense sources of prey animals in order to be cued to nest, and to nest successfully. Their reproduction may thus reflect something about the healthy dynamics of prey animal populations. This is probably not a simple relationship, since dense populations may require one or more kinds of irregular disturbance to achieve pulsed production (Frederick and Ogden in press). Storks also seem to rely throughout their range on some degree of surface water recession in order to concentrate prey animals - successful foraging therefore relies on the right mix of water depth, and water level recession. Thus the regular, successful reproduction of storks may indicate that the combination of several hydrological and biological functions in the Everglades has been correctly restored. Reliance on the storks as an indicator seems wise, since we have a long record of stork nesting (over 80 years), and almost no information on dynamics of aquatic animal populations prior to drainage of the system.

Although the restoration of the south Florida Ecosystem is well underway, considerable uncertainties remain about the reproductive responses of storks, including how soon storks might respond to a restored ecosystem, where and when they will nest, the relative importance of wetland areas outside the Everglades, and how the population will respond to specific levels of reproductive productivity. This proposal is designed to address two areas of uncertainty - understanding demographic responses, and understanding the importance of wetlands outside the south Florida area.

Demographic responses:

Although considerable information exists about the reproductive ecology of storks (e.g. fecundity [Coulter et al. 1999], historical fluctuation in nesting numbers [Ogden 1994], behavior [Kahl 1972], reproductive responses to hydrology [Kushlan et al. 1975, Ogden 1994] food ecology [Kahl 1964], energetics [Kahl 1962, 1963]) there is almost no information about juvenile or adult survival (Coulter et al. 1999). The lack of this information means that it is impossible to construct justifiable demographic models for this species. This is because in long-lived species, which probably includes storks, survival of adults and young may have a vastly greater impact on demographic change than does variation in fecundity. The lack of survival estimates means that it is impossible to calculate the level or periodicity of reproduction needed to maintain a stable population, to understand whether the south Florida area is a net sink or production area for the southeastern population, or to predict population responses to specific habitat loss or improvement. This problem stems from the logistical difficulties of obtaining survival estimates for young and adult birds, which may wander over the entire southeastern United States, and for which site fidelity is (for purposes of traditional mark-resighting methods) fairly low.

Importance of wetlands outside of south Florida:

Storks breeding in south Florida are known to be a subset of the fluid and panmictic southeastern U.S. population (Stangel et al. 1990), and south Florida breeders have no distinction as a genetic subpopulation. Early banding studies have also shown that storks breeding in south Florida move widely throughout the year. However, there are no formal surveys in the storks range designed to document where storks may be found at any one time, and as a result there is little specific information about the wetland areas used by storks, particularly in the nonbreeding season. This lack of information is of relevance to the south Florida restoration effort, since storks typically move out of south Florida during the rainy season, and rely on wetlands elsewhere for a considerable portion of the year. Studies of the movements of individual storks would therefore lead to the identification of specific wetland areas used most heavily. This knowledge would be instrumental in enhancing the management of the broader southeastern U.S. population. It would also be of key importance in assessing the relative impact to the storks of ecological restoration in the Everglades.

Required work:

Task 1 - Monitoring of wading bird reproduction in Water Conservation Areas (WCAs) 1, 2, and 3

Monitor wading bird reproductive responses in WCAs 1, 2 and 3 using the same standardized techniques that have been employed since 1986.

Conduct monthly systematic aerial surveys over WCAs 1, 2, and 3, that are 100% coverage and designed to locate and count colonies of birds. Surveys are flown at 800 ft AGL, with one observer on each side of the aircraft, in east-west oriented transects spaced 1.6 nautical miles apart. This transect spacing has been shown to provide overlapping visual coverage of colonies. Colonies located shall be circled and counted, and aerial photographs shall be taken to help count numbers of birds. In an effort to correct counts for survey bias, measure the counting biases of individuals using the Wildlife Counts software. Observers shall be initially trained using this program with immediate feedback about true numbers of birds. Following a standardized training program, observers shall be tested on a standardized set of randomly picked numbers without feedback in order to establish their counting biases.

Comprehensive ground surveys shall also be conducted of the entire area that is wetted, using GPS-guided systematic airboat transects. Every tree island shall be approached closely enough to flush nesting birds, and nests and species compositions counted for each colony. These surveys shall take place between mid March and early June of each year.

Task 2 - Measurement of juvenile Wood Stork survival and movements

In support of tasks 3, 4, and 5, the lack of information about stork survival shall be addressed by studying the survival and movements of individual storks through the use of satellite telemetry. The use of satellite or PIT tags is a cheaper and more effective alternative than either conventional radio telemetry, or use of capture/mark/recapture techniques. Thirty PIT tags shall be placed on young storks to follow their movements and survival as they become adults and breed. The determination of sample size is based on the ability to achieve reasonably low standard deviations in average survival rate estimates for both adults and young. Young storks shall be captured and tagged during the period immediately prior to the attainment of flight abilities and departure from the nest. 15 - 18 gram solar powered PIT tags shall be placed in a back-pack style harness, and a 8 - 10 g VHF transmitter shall also be mounted on the backpack (total package estimated at 30 g, well within the 3% of body mass limit suggested by USFWS). The purpose of the VHF transmitter is to allow fine scale location of the individual. PIT tags rarely allow less than one km accuracy, while VHF tags may allow less than 4 m 2 accuracy. If a dead bird can be recovered using the VHF tags, the PIT tag could be reused to mark other birds, thereby increasing the sample size.

Storks that fledge from colonies located in south Florida, and preferably from the Everglades, shall be studied. Although there is a reasonable chance that storks will be successful enough to produce young, there is also the possibility that no nesting will occur, or that nesting will be unsuccessful. In the event of the latter, young storks that fledge from other colonies in south Florida (eg, southwest Florida, West Palm Beach), or failing that, other colonies in Florida shall be studied. While demographic information from the Everglades is preferable for the parameterization of a demographic model of south Florida storks, measurements of survival from colonies outside of the Everglades is far preferable to no survival estimates at all.

Positions of active storks shall be monitored on a daily basis via satellite downlink through the ARGOS service network.

The resulting information shall be used in several ways:

Task 3. Development of a demographic model for Wood Storks.

Using a combination of existing fecundity and life history information, and the information on survival and age at first reproduction from this study, a computer-based demographic model for Wood Storks shall be developed. Survival shall be estimated using Kaplan-Meier estimators that allow correction for lost (censored) tags. In conjunction with population biologists currently at University of Florida, custom stochastic models shall be developed. Models shall be used specifically to determine fecundity necessary for stable age distribution and stable population, and sensitivity (elasticity) of the model to various assumptions and demographic parameters.

Task 4. Identification of wetland areas commonly used by Wood Storks

Identification of wetland areas commonly used by Wood Storks, both inside and outside the south Florida area, as well as the relative importance of these wetlands shall be measured in proportion of annual time spent in those habitats. Using only high-quality fixes on individual birds, we will compare the use of wetland habitats with availability of habitats through a GIS analysis throughout the southeastern US. This information shall be analyzed to determine whether choice of habitat has any statistical effect upon survival of young storks.

Task 5. Development of an interactive website

Development of an interactive website for educational purposes, shall show the most up to date location information for individual storks, past tracking maps, and general information about storks, wetland conservation, and the project.


A progress report shall be submitted by August 30. This report shall outline the summary of nesting in the Everglades for the current year, and progress on studies of Wood Stork survival and movements. A second interim shall be submitted by December 30, and a final report by March 2004. The annual report shall contain full documentation of all work carried out during the calendar year, with appropriate analyses and presentation of datasets.

Progress status reports shall be submitted every April and August that will include a summary of all activities for the current period and progress status of ongoing activities. An annual report shall be submitted every December that will include a comprehensive status report of all activities conducted in the calendar year. The annual report shall contain full documentation of all work carried out during the calendar year, with appropriate analyses and a presentation of datasets.

The final report shall include all the datasets, the demographic model with documentation, maps of the wetland areas used by Wood Storks, and the complete and functional website. The final report shall be completed by January 2005.

Literature Cited

Bennetts, R. E. V. J. Dreitz W. M. Kitchens J. E. Hines and J. D. Nichols. 1999. Annual survival of Snail Kites in Florida: Radio telemetry versus capture-resighting data. AUK 116: 435-47.

Coulter, M. C. J. A. Rodgers J. C. Ogden and F. C. Depkin. 1999. Wood Stork. Birds of North America, A. Poole and F. Gill, Eds No. 409: 1-28. The Birds of North America, Inc. Philadelphia Pa.

Frederick, P.C. and J.C. Ogden. In press. Pulsed breeding of long-legged wading birds and the importance of infrequent severe drought conditions in the Florida Everglades. Wetlands.

Kahl, M. P. 1962. Bioenergetics and growth of nestling Wood Storks. Condor 64:169-183.

---. 1972. Comparative ethology of the Ciconiidae. The Wood Storks (genera Mycteria and Ibis). Ibis 114:15-29.

Kahl, M. P. Jr. 1963. Thermoregulation in the Wood Stork, with special reference to the role of the legs. Physiological Zoology 36: 141-51.

Kahl, M. Philip, Jr. 1964. Food ecology of the Wood Stork (Mycteria americana) in Florida. Ecological Monographs 34, no. 2: 97-117.

Kushlan, J. A., J. C. Ogden, and A. L. Higer. 1975. "Relation of water level and fish availability to Wood Stork reproduction in the southern Everglades." U.S. Geological Survey Open-file Rept., U.S. Geological Survey, Tallahassee, Florida.

Ogden, J. C. 1994. A comparison of wading bird nesting dynamics, 1931-1946 and 1974-1989 as an indication of changes in ecosystem conditions in the southern Everglades. Pgs. 533- 570 in: S. Davis and J.C. Ogden (eds). Everglades: the ecosystem and its restoration. Del Ray Beach, Florida: St. Lucie Press.

Stangel, P. W., Jr. J.A. Rodgers, and A.L. Bryan. 1990. Genetic variation and population structure of the Florida Wood Stork. Auk 107: 614-19.

Tiner, R. W. 1984. Wetlands of the United States: Current status and recent trends. National Wetlands Inventory, U.S. Fish and Wildlife Service Washington D.C.

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