Winter Shorebird Survey FINAL PERFORMANCE REPORT November 1, 1993–March 1, 1994 Gary L. Sprandel Jeffery A. Gore David T. Cobb February 1997 Florida Game and Fresh Water Fish Commission 620 South Meridian Street Tallahassee, FL 32399-1600 Winter Shorebird Survey Gary L. Sprandel1 Jeffery A. Gore2 David T. Cobb1 1Florida Game and Fresh Water Fish Commission Route 7, Box 3055 Quincy, FL 32351 2Florida Game and Fresh Water Fish Commission 3911 Highway 2321 Panama City, FL 32409 Final Performance Report November 1, 1993–March 1, 1994 Survey and monitoring project 7704 February 1997 Suggested citation: Sprandel, G. L., J. A. Gore, and D. T. Cobb. 1997. Winter shorebird survey. Florida Game and Fresh Water Fish Comm. Final Perf. Rep. Tallahassee. 162 pp. + vi. ii WINTER SHOREBIRD SURVEY GARY L. SPRANDEL1 JEFFERY A. GORE2 DAVID T. COBB1 1Florida Game and Fresh Water Fish Commission, Route 7, Box 3055, Quincy, FL 32351 2Florida Game and Fresh Water Fish Commission, 3911 Highway 2321, Panama City, FL 32409 Abstract: We surveyed the coast of Florida in winter 1993–94 to identify important sites for wintering shorebirds. From November to mid-December 1993, we identified 273 sites from the ground and 217 sites from aircraft. Indices of biological importance and potential for adverse impacts were developed and applied to these initial sites. The 60 sites with the highest biological ranking were visited at least 4 more times between mid-December 1993 and 1 March 1994 and we counted 134,442 shorebirds of 20 species during these visits. Of the top 60 sites, 53 were on Florida’s west coast. Nine sites had very high biological scores: 6 near Tampa Bay, 2 in Florida Bay, and 1 near Apalachicola Bay. Eighteen sites had a moderate or high potential for large numbers of shorebirds to be impacted by human activities. Most were in Tampa Bay or on nearby barrier islands. The number of birds counted at each of the 60 study sites varied widely among visits (mean coefficient of variation [CV] for all shorebirds counted on a site visit was 0.86; when counts were grouped by species, the mean CV of all counts was 1.5). Increasing the number of visits at a site did not reduce the CV for total shorebirds counted. Only for a few sites could the CV be reduced by using just counts made during specific tidal conditions. We prepared power analysis procedures to predict the number of visits required to detect a population trend. Simulations indicated that with a CV of 0.6 at least 5 visits per year for 10 years would be required to detect a 10% annual decline in shorebird numbers at an Alpha of 0.05. At that rate, monitoring any but the most important sites would likely be impractical. We recommend monitoring, at a minimum, the 9 most important sites plus at least 2 sites in each coastal region 4 times each winter. Monitoring other locally important or easily accessible sites would be valuable. Additional surveys, with at least 2 visits per site, would provide a more accurate view of important sites for wintering shorebirds in Florida, particularly in Tampa Bay, Florida Bay, and Northeast Florida. In addition to monitoring bird numbers, conservation actions such as educating visitors about shorebirds, posting areas against disturbance, monitoring contaminants, managing water levels, and seeking acquisition or other formal protection should be initiated. We identify general conservation needs for the 29 most important winter shorebird sites. iii TABLE OF CONTENTS ABSTRACT . .iii INTRODUCTION . .1 STUDY AREA . .2 METHODS . .4 Pilot Study Surveys . .4 Statewide Surveys . .5 Accuracy of Survey Results . .10 Ranking the Final Sites . .11 Monitoring Winter Shorebird Numbers . .16 Trend Detection . .17 Power and Sample Size . .17 Detection of Statewide Trends from Multiple Sites . .19 RESULTS AND DISCUSSION . .19 Shorebird Distribution and Abundance . .19 Influences upon Local Distribution and Abundance . .53 Accuracy of Survey Results . .64 Ranking Winter Shorebird Sites . .74 Potential Impact to Sites . .84 Monitoring Winter Shorebird Numbers . .93 Trend Detection . .100 Power and Sample Size . .102 Conclusions about Trend Detection . .106 Detection of Overall Trends from Multiple Sites . .108 Sampling Sites within the State . .108 What a Trend at a Site in Florida Means . .110 MANAGEMENT IMPLICATIONS . .110 Conservation of Shorebirds . .110 ACKNOWLEDGMENTS . .118 LITERATURE CITED . .119 APPENDICES . .135 v WINTER SHOREBIRD SURVEY—Sprandel et al. 1 INTRODUCTION Shorebirds comprise a diverse group of short-legged wading birds that inhabit the margins of inland or coastal waters (Hayman et al. 1986). Most shorebird species breed in interior locations, often at high latitudes, and move to coastal areas in the nonbreeding season (Burger 1984a). Many species that breed in arctic regions of North America migrate along the Atlantic and Gulf coasts on their way to more distant wintering grounds. Florida serves as a feeding and resting stop each spring and fall for many of these migrating shorebirds, but for others, Florida is the winter destination. At least 25 species reside in the state during winter and the conservation of these wintering species is the focus of this report. The current and future status of Florida’s shorebird populations is of concern because much of the coast has been developed for human use and is vulnerable to further development, pollution, or disturbance (Fernald and Purdum 1992). Because of these threats and the lack of knowledge of shorebird population sizes or trends, the Bureau of Nongame Wildlife of the Florida Game and Fresh Water Fish Commission (FGFWFC) identified shorebirds as a group of coastal wildlife species needing conservation attention and, especially, surveys of their distribution and abundance (Millsap et al. 1990, 1991). The current assessment of shorebird abundance and distribution in Florida focused on wintering birds rather than breeding or migrating birds. Because few species breed in the state, surveys of breeding shorebirds would have addressed few species or individuals. Migrating shorebirds are more common, but reliable estimates of migrating shorebirds are difficult to obtain because of the high daily variation and turnover in bird numbers (Thompson 1993). Wintering shorebirds are more common than breeding shorebirds in Florida and more easily counted than migrants. More importantly, they may be most in need of attention. Impacts from habitat degradation, pollution, and human disturbance may affect shorebirds most severely on their winter range because most species spend considerable time on the wintering grounds and the energy stress due to severe weather and scarce food is often greatest in winter (Baker and Baker 1973, Senner and Howe 1984). For these reasons, we decided that conservation efforts directed toward populations of wintering shorebirds offered the greatest benefits to the greatest number of shorebirds in Florida. We focused on coastal habitats because we assumed that coastal sites supported more shorebirds and presented more potential impacts than interior sites and because access to many interior sites was limited. 2 FLORIDA GAME AND FRESH WATER FISH COMMISSION FINAL PERFORMANCE REPORT The objectives of this study were to: (1) identify, by species, the relative distribution and abundance of wintering shorebirds along Florida’s coast, (2) rank shorebird roosting and foraging sites based upon biological importance and vulnerability, (3) describe the variation in estimates of the number of wintering shorebirds and discuss its effects upon monitoring trends in wintering populations, and (4) suggest needs and means for conserving the most important sites. STUDY AREA The coast of Florida is not ecologically homogeneous (Livingston 1984); therefore, we divided the coast into 6 distinct regions based upon ecological conditions that we suspected would differentially influence shorebird abundance (Fig. 1). The factors we evaluated included tidal variation, water depth, abundance of aquatic vegetation, influx of fresh water, presence of protected waters, and availability of sandflats or mudflats. These factors are not independent and they affect not only the physical features shorebirds require for roosting and feeding but also the conditions necessary for their invertebrate prey to be abundant. The Panhandle coast (Fig. 1) has moderate-energy waves, diurnal tides, and a broad salinity gradient (Fernald and Purdum 1992). This coastal region is also distinguished by the abundance of largely undeveloped barrier islands, broad bays, and large rivers (Wolfe et al. 1988). In contrast to the Panhandle coast, the Big Bend coast (Fig. 1) represents a very low-energy wave system with broad shallow waters, expansive salt marsh, and freshwater influx from smaller rivers and streams (Livingston 1984). The southwest coast (Fig. 1), like the Panhandle, has many barrier islands, large bays, and features moderate-energy waves. Winter temperatures, however, are warmer than in the Panhandle, and mangroves, which are absent to the north, line much of the shoreline of bays and inlets (Fernald and Purdum 1992). Most of the southwest coast, particularly along the sandy beaches, has been highly developed for human use. The Everglades coast, at the southern tip of the Florida peninsula (Fig. 1), is characterized by narrow mangrove-lined shores, sediments with relatively high organic content and shell or coral fragments, and low-energy waves (Fernald and Purdum 1992). We included the Florida Keys in this region, even though the outer coast of the Keys represents a high-energy wave system more typical of the coast to the north. WINTER SHOREBIRD SURVEY—Sprandel et al. 3 We defined 2 survey regions along the Atlantic coast (Fig. 1) and both regions have high-energy waves and semidiurnal tides. The southeast coast (Fig. 1), extending from northern Biscayne Bay (Dade County) to Sebastian Inlet (Indian River County), is characterized by narrow shorelines that have been intensively developed. The northeast coast (Fig. 1) has colder winter temperatures, greater tidal fluctuations, and more bays or lagoons than the southeast coast (Fernald and Purdum 1992).