wading bird populations of the kennedy space center

WADING BIRD POPULATIONS OF THE KENNEDY SPACE CENTER

Most wading bird habitat at the northern Indian River Lagoon (IRL) complex occurs on Kennedy Space Center (KSC). Monthly aerial and roadside surveys have been conducted for wading birds (Ciconiiformes) on KSC since 1987. Three potential feeding habitats were surveyed: mosquito control impoundments, edges of the estuary, and roadside ditches and canals. Wading birds used mosquito control impoundments extensively for feeding, particularly the open water areas. Four seasons [winter (Oct.-Jan.), prenesting (Feb.-Mar.), nesting (Apr.-Jun.), and postnesting (Jul.-Sep.)] were determined from average population trends. Total numbers of birds counted were highest during the nesting season and lowest in winter, indicating seasonal shifts in populations on a regional scale. Estimates of KSC population sizes were determined from abundances within the feeding habitats, the amounts of available habitats, and colony counts of breeding populations. KSC was determined to be an important area within the IRL and the state of Florida for several species of wading birds.

Most of the northern Indian River Lagoon (IRL) system lies within the confines of the Kennedy Space Center (KSC) (Swain et aI., 1995: Fig. I). KSC is a transition zone between the temperate and subtropical biotic regions, and provides habitat for remarkably diverse assemblage of plants and animals (DeFreese, 1991; Breininger et aI., 1994). The need for an economic, non-toxic method of mosquito control on KSC became apparent in the 1950s. Flooding the marshes reduced mosquito populations because the salt marsh mosquito (mostly Aedes taeniorhyncus) must lay its eggs on exposed mud (Provost, 1967). As a result, all of the salt marsh on KSC was impounded by the mid-1960s. Early management practices flooded most impoundments continuously, so that the native marsh vegetation died and large expanses of open water resulted. This may have increased the feeding habitat for wading birds in the IRL (Trost, 1968; Provost, 1969). Concurrently, wetlands habitat in the St. Johns River basin has been permanently altered or destroyed (Kushlan, 1990). Seasonal data are needed to quantify the significance of KSC habitats to resident and migratory populations of wading birds of the IRL. Our objectives in this study were to: 1) investigate the relative importance of the major categories of feeding habitats on KSC to wading birds; 2) determine the seasonal use of those feeding habitats by wading birds; 3) quantify wading bird nesting in KSC colonies; and 4) estimate the total population of wading birds using KSC during each season.

Wading bird feeding habitat surveys were conducted between April 1987 and March 1991. Surveys were done once per month from 0900-1100 in a NASA Huey helicopter at an altitude of 60 m and a speed of 60 kn. Approximately 20% of the nearly I 1,000 ha of impoundment habitat and 16% of the 450 krn of estuarine edge available on KSC were covered. In the impoundments, bird species and the cover type in which they were feeding (open water, salt marsh vegetation, or cattail) were identified. The estuarine edge was surveyed by flying approximately 300 m off the shoreline over the water, identifying and counting birds that were feeding along the land/water interface or in the water. The feeding habitat study also included surveys of the 539 km of roadside ditches. An established route of 62 km was driven monthly and birds using the ditches were counted. A Chi square analysis was done to test if the birds were feeding randomly within the impoundment

,

9000

8000

1\ 1\ 7000

I I I

6000 I I 5000

I

11l

1" ii

'0 l!! .c E :J c:

I I

4000 I I

OJ

3000

I I I

2000

\ \ \ \ \ \ \ \ \ \ \ \ \ \

1000

a sap month

Figure I. The total numbers of wading birds counted nedy Space Center, April 1987-March 1991.

in survey impoundments

and estuary

on Ken-

3000

2500

2000

1"'"

ii

15

1500

••c:

'"E Ql

1000-

500

a

Figure 2. Mean number and 95% confidence limits of wading birds in Kennedy impoundments and estuary, April 1987-March 1991.

Space Center survey

232 350

300

250

1"'"

200

i'i

'0

•• c

'E"

150

Q)

100

50

Figure 3. Mean number and 95% confidence estuary, April 1987-March 1991.

limits of wading birds in Kennedy Space Center survey

vegetation cover types. Expected values were determined from the proportions of the cover types present in the impoundments surveyed (Provancha et a!., 1986). Wading birds on KSC nest on natural and spoil islands in the 1RL. Colonies were surveyed from 1987-1993, excluding 1991 when only wood storks nests were counted. Colonies were visited one time during late April/early May when most species were incubating eggs or had small nestlings, so that at least one parent attended each nest (Cruickshank, 1980). A boat was driven slowly around each island and counts were made of nests by species. Based on wading bird breeding chronology and seasonal abundance, we determined four seasons to describe trends in wading bird numbers: prenesting (Feb.-Mar.), nesting season (Apr.-Jun.), postnesting (Jul.-Sep.), and winter (Oct.-Jan.). A population estimate of the total number of wading birds on KSC was determined for each season. Abundance estimates for impoundments, estuarine edges, and ditches from the feeding habitat study were multiplied by the amounts of those habitats available on KSC (Provancha et a!., 1986). The average number of adult birds sitting on nests at the colonies was added to the totals from the feeding habitats for the nesting season estimate. Colony sites were surveyed throughout the seasons, but very few birds were present during survey hours except in the nesting season. The importance of KSC as a wading bird population center in Florida was evaluated. KSC was considered a population center if it supported at least 10% of the estimated nesting population of a species or if the KSC nesting population was one of the ten largest Florida populations. Population estimates were based on colony censuses (Runde et a!., 1991; Nesbitt et a!., 1982; Spendelow and Patton, 1988; Osborn and Custer, 1978) and individual species accounts (Breininger et a!., 1994). RESULTS

Much variation in the numbers of wading birds counted occurred across the same month in different years (Fig. 1), but numbers during winter were consistently lower than other seasons. Ninety-two percent of the total birds counted were feeding in impoundments, with the highest numbers in the prenesting season and the lowest in winter (Fig. 2). The seasonal pattern in the estuary differed in that the lowest numbers were in the prenesting and nesting seasons and the highest numbers were during the postnesting season (Fig. 3). The numbers in the estuary were also low in winter.

Table I. Summary (excluding 1991)

of wading bird nesting on major colonies on Kennedy

t Underestimates; =1=Includes 1991.

Range

± ± ± ± ± ± ± ± ± ± ± ± ±

69-150 271-592 184-1,224 11-65 188-733 9-17 41-450 0-12 3-30 715-7,226 50-423 1-28 0-122

32 109 358 22 193 3 145 4 9 2,318 117 9 54

3,904 ± 3,220

Total nests * Underestimates;

Number of nests (average ± SD)

113 385 442 33 368 14 188 4 12 2,112 174 9 48

Great blue heron Great egret Snowy egret Little blue heron Tricolored heron Reddish egret Cattle egret* Green-backed heront B-c night-heront White ibis Glossy ibis Roseate spoonbill Wood stork:j:

Space Center, 1987-1993

surveys taken all appropriate

prior to height of cattle egret nesting nesting habitats not surveyed.

season.

Seventy-two percent of the birds feeding within the impoundments were using open water, 24% were in salt marsh vegetation, and 2% were in cattail. If the birds were distributed randomly throughout the cover types, 29% would be expected in open water, 45% in salt marsh vegetation, and 19% in cattail. Chi square analysis showed that these differences were significant (P < 0.001). Thirteen species of waders used between four and nine colony sites on KSC each year (Table 1). The mean number of nests per year was 3,904, but much variation occurred. White ibises had the largest average nesting population. Roseate spoonbills, first reported nesting on KSC in 1987 (Smith and Breininger, 1988), nested in small numbers each year (Table 1). The number of wood stork nests on KSC ranged from 0 to 122, with no successful nesting for the last 3 years. Wading bird abundance estimates in the impoundments ranged from 0.24 birds·ha-' in winter to 0.92 birds·ha-' during the prenesting season (Table 2). There were between 0.94 birds·km-l in the estuary during prenesting and 3.09·km-1 during postnesting (Table 2). The total population estimate was 11,365 birds inhabiting KSC during prenesting, with a high of more than 14,000 birds during nesting season, 10,000 during postnesting, and about 5,000 birds in winter (Table 3). KSC was determined to be a Florida population center (i.e., supported 10% of the Florida nesting population or was one of the ten largest nesting populations in Florida) for the wood stork, roseate spoonbill, reddish egret, glossy ibis, white ibis, snowy egret, and tricolored heron.

Table 2. Abundances of wading birds in Kennedy April 1987-March 1991

Impoundments (#·ha I) Estuary (#·km-I)

0.92 0.94

Space Center survey impoundments

0.78 1.14

0.68 3.09

0.24 1.48

and estuary,

0.62 1.66

Table 3. 1991

Population

estimate for wading birds using the Kennedy

Space Center, April 1987-March

Number of birds Prenest

Impoundments Estuary Roadside ditches Nesting on spoil islands Total

Nesting

Postnesl

Winter

9,782 424 1,159

8,293 514 1,353 3,904

7,230 1,394 1,391

2,552 667 1,692

11,365

14,064

10,015

4,911

KSC is an important area for wading bird populations regionally and statewide, and is becoming increasingly important for some species. A northern breeding range extension of the roseate spoonbill occurred on KSC in 1987; spoonbills have continued to nest there since that time (Smith and Breininger, 1988; Smith and Breininger, unpubl. data). Hundreds of non-nesting spoonbills commonly occur on KSC (Smith and Breininger, unpubl. data). In the 1960s, reddish egrets were rarely seen in local surveys (Trost, 1968), but now often occur in small numbers feeding in open water impoundments and along the edges of the estuary (Breininger and Smith, 1990; Smith and Breininger, unpubl. data). One colony on KSC has been recognized as the most significant area for reddish egrets on the central Florida east coast (Paul, 1986). The number of wood storks in northern and central Florida has nearly doubled since 1960, in contrast to the decline in south Florida (Ogden, 1991). Wood storks were first recorded nesting on KSC in 1972 and the number of nests has occasionally approached 10% of the Florida population (Clark and Lee, 1982). The variation in wood stork nesting on K~C from 1987 through 1994 (between 0 and 122 nests per year) is probably due to several severe freezes that destroyed or stunted mangroves that are used for nest sites (Smith and Breininger, unpubl. data). The wood stork nesting population on KSC also varies with water level fluctuations across the region, especially in the St. Johns River, which is believed to be the primary feeding area during the breeding season (Clark, 1978). The among-year variation in the total numbers of wading birds using KSC can be attributed to several factors. There are population shifts within and among regions in the southeastern U.S. related to hydrological influences and prey abundance and availability (Gilmore, 1987; Kushlan, 1976; Clark, 1978; Rodgers et aI., 1987). Large-scale population shifts may also be due to the ability of wading birds to move long distances to find suitable nesting conditions. Abandonment of some of the traditional southern Florida sites is a result of habitat degradation associated with drainage (Kushlan and White, 1977), and some species' nesting ranges are extending northward (Coulter, 1989; Runde, 1991; Smith and Breininger, 1988). Essentially little is known about seasonal shifts in wading bird populations attributed to prey conditions, migrations, and management practices (Breininger and Smith, 1990). The comparatively small wading bird population on KSC in winter may be due to artificially high water levels needed to support the large wintering waterfowl population. Increases in abundance of wading birds have been attributed to declining water levels which concentrate prey (Kush lan, 1976; Breininger and Smith, 1990). Wading bird abundance has increased in winter

elsewhere in the IRL and St. Johns River associated with declining water levels in winter (Gilmore, 1987; Schikorr and Swain, 1995). Roadside ditches are readily used for feeding by wading birds. They may provide alternative habitat to replace natural wetlands that have been developed or degraded. Ditches are often managed for weed control and/or receive environmental contaminants which may influence wading bird populations or their prey. The edges of the estuary did not support feeding by nearly as many wading birds as the impoundments, but there was an increase in estuarine use during the postnesting season which coincided with seasonally lower water levels. It is unclear if this increase was a result of improved feeding conditions in the estuary or poorer feeding conditions in the impoundments. Alternatively, juvenile waders may use the estuary because they prefer to feed close to the colony or are inexperienced at finding the best habitat. Adults with young on the nest may be limited in the distance they can travel from the colony or it may be more efficient for them to make many short food-gathering trips to the estuary than to travel to impoundments that are further away. The open water areas of mosquito control impoundments provided the vast majority of feeding habitat for wading birds. Flooding to support KSC's wintering waterfowl population allows fish to remain in areas that would normally be dry. When spring drawdown occurs, these fish become available during the waders' reproductive season when energy demands are highest (Kushlan, 1978). Shallow open water is also used by migrating and wintering shorebirds (Breininger and Smith, 1990). Efforts are currently underway on KSC and throughout the IRL to reestablish the connection between mosquito control impoundments and the estuary. The major objective on KSC is to restore the impoundments to a more naturally functioning salt marsh ecosystem while retaining mosquito control. Culverts with riser boards are placed between the impoundments and estuary, allowing managers to choose whether to manipulate water flow and direction, or let natural fluctuations occur. One of the first management goals is to reduce cattail cover by pumping brackish water from the estuary and holding it in the impoundments. Our results showed that the reduction in cattails and concurrent expansion of open water areas should benefit wading birds by increasing the amount of feeding habitat.

This research was funded by NASA and supported by the cooperation of B. R. Summerfield, W. K. Knott, III, D. F. Doerr, and A. M. Koller, Jr. (formerly) of the NASA Biomedical Operations and Research Office, Kennedy Space Center. J. Harvey prepared the figures. H. Swain, K. Schikorr, and two anonymous reviewers provided helpful comments on earlier drafts. We gratefully acknowledge the NASA pilots, D. Bahm, J. Jackson, S. Nelson, E. Taff, and N. Violette, whose skill and professionalism made our surveys not only efficient, but pleasant.

Breininger, D. R. and R. B. Smith. 1990. Waterbird use of coastal impoundments and management implications in east-central Florida. Wetlands 10: 223-241. ---, M. J. Barkaszi, R. B. Smith, D. M. Oddy and J. A. Provancha. 1994. Endangered and potentially endangered wildlife on John F. Kennedy Space Center and faunal integrity as a goal for maintaining biological diversity. NASA Tech. Memo. 451 pp. Clark, E. S. 1978. Factors affecting the initiation and success of nesting in an east-central wood stork colony. Proceedings of the Colonial Waterbird Group 2: 178-188. --and R. C. Lee. 1982. History and status of wood stork nesting on Merritt Island National Wildlife Refuge. Internal report. Merritt Island National Wildlife Refuge, Titusville, Florida. Coulter, M. C. 1989. Wood storks of the Birdsville Colony and swamps of the Savannah River Plant.

1988 Annual Report. SREL-37/UC-66e. Savannah River Ecology Laboratory, Aiken, South Carolina. 284 pp. Cruickshank, A. D. 1980. The birds of Brevard County. Florida Press, Inc., Orlando, Florida. 206 p. DeFreese, D. E. 1991. Threats to biological diversity in marine and estuarine ecosystems of Florida. Coast. Manage. 19: 73-101. Gilmore, R. G. 1987. Fish, macrocrustacean, and avian population dynamics and cohabitation in tidally influenced impounded subtropical wetlands. Pages 373-394 in W. R. Whitman and W. H. Meredith, eds. Proceedings of a Symposium on Waterfowl and Wetlands Management in the Coastal Zone of the Atlantic Flyway. Delaware Department of Natural Resources and Environmental Control, Wilmington, Delaware. Kushlan, J. A. 1976. Wading bird predation in a seasonally fluctuating pond. The Auk 88: 464--476. ---. 1978. Feeding ecology of wading birds. Pages 249-298 in A. Sprunt, IV, J. C. Ogden and S. Winckler, eds. Wading birds. National Audubon Society, New York, New York. ---. 1990. Freshwater marshes. Pages 324-363 in R. L. Myers and J. J. Ewel, eds. Ecosystems of Florida. University of Central Florida Press, Orlando, Florida. --and D. A. White. 1977. Nesting wading bird populations in southern Florida. Fla. Sci. 40: 65-72. Nesbitt, S. A., J. C. Ogden, H. W. Kale, II, B. W. Patty and L. A. Rowse. 1982. Florida atlas of breeding sites for herons and their allies: 1976-78. FWS/OBS-81/49. U.S. Fish and Wildlife Service Office of Biological Services, Washington, D.C. 450 pp. Ogden, J. C. 1991. Nesting by wood storks in natural, altered, and artificial wetlands in central and northern Florida. Colonial Waterbirds 14: 39--45. Osborn, R. G. and T. W. Custer. 1978. Herons and their allies: atlas of Atlantic Coast colonies, 1975 and 1976. FWS/OBS-77/08. U.S. Fish and Wildlife Service Biological Services Program, Washington, D.C. Paul, R. T. 1986. Florida region. Am. Birds 40: I 194. Provancha, M. J., P. A. Schmalzer and C. R. Hinkle. 1986. Vegetation types (maps). NASA, Biomedical Operations and Research Office, Kennedy Space Center, Florida. Provost, M. W. 1967. Managing impounded salt marsh for mosquito control and estuarine resource conservation. Pages 163-171 in J. D. Newson, ed. Proceedings of the Louisiana State University Marsh and Estuary Management Symposium. Louisiana State University, Division of Continuing Education, Baton Rouge, Louisiana. ---. 1969. Ecological control of salt marsh mosquitos with side benefits to birds. Proceedings of the Tall Timbers Conference of Ecological Animai Control by Habitat Management I: 193-206. Rodgers, J. A., A. S. Wenner and S. T. Schwikert. 1987. Population dynamics of wood storks in north and central Florida. Colonial Waterbirds 10: 151-156. Runde, D. E. 1991. Trends in wading bird nesting populations in Florida, 1976-1978 and 1986-1989. Final Performance Report. Florida Game and Freshwater Fish Commission, Division of Wildlife, Nongame Wildlife Section, Tallahassee, Florida. 90 pp. ---, J. A. Gore, J. A. Hovis, M. S. Robson and P. D. Southall. 1991. Florida atlas of breeding sites for herons and their allies: update 1986-89. Florida Game and Freshwater Fish Commission, Division of Wildlife, Nongame Wildlife Section, Tallahassee, Florida. 147 pp. Schikorr, K. E. and H. M. Swain. 1995. Wading birds-barometer of the Indian River Lagoon. Bull. Mar. Sci. 57: 215-229. Smith, R. B. and D. R. Breininger. 1988. Northern breeding range extension for the roseate spoonbill in Florida. Fla. Field Nat. 16: 65-67. Spendelow, J. A. and S. R. Patton. 1988. National atlas of coastal waterbird colonies in the contiguous United States: 1976-82. U.S. Fish and Wildlife Service BioI. Rep. 88(5). 326 pp. Swain, Hilary M., D. R. Breininger, D. S. Busby, K. B. Clark, S. A. Cook, R. A. Day, D. E. De Freese, R. G. Gilmore, A. W. Hart, C. R. Hinkle, D. A. McArdle, P. M. Mikkelsen, W. G. Nelson and A. J. Zahorcak. 1995. Introduction. Bull. Mar. Sci. 57: 1-7. Trost, C. H. 1968. Study of wildlife usage of salt marsh on east coast of Florida before and after impoundment for mosquito and sandfly control. Final Rep. Bureau of Sport Fisheries and Wildlife. U.S. Fish and Wildlife Service Contract No. 14-16-0008-623.