One of the objectives of the Wood Stork Recovery Plan developed by the U.S. Fish and Wildlife Service, identified productivity levels exceeding a minimum standard to ensure continued viability of the stork population in the United States. Specifically, knowledge of the number of fledged young per nest, or birds mature enough to leave the next, must be determined for a representative number of colonies during the same year for a minimum of three years.
The reclassification from endangered to threatened could be accomplished when there are 6,000 nesting pairs and annual productivity is greater than 1.5 fledglings per nest calculated over a three-year average.
Thus, the primary goal of this study is to gather productivity data for storks nesting in Florida in order to examine the variation and trends in fledging success within and among colonies and years.
The project duration will include the breeding seasons from 2003 to 2009. The data on the reproductive success of the north and central Florida stork colonies will be compared with the storks in the southeastern United States by examining the effects of colony size and geographical location on breeding success within and among colonies and years. These data ultimately will be used to determine if the stork population in the United States meets recovery criteria for downlisting the species.
Between 15 to 20 active wood stork colonies in north and central Florida are being monitored by FWC personnel for 3-5 continuous nesting seasons. These sites include both marine estuarine sites along the coast and interior freshwater sites. Concurrent studies are occurring in both Georgia and South Carolina.
Field research entails marking and monitoring nests from March to August. Either all nests (colonies less than #100 nests) or a sample of the nests (for example, 25-50 percent of nests at larger colonies) are monitored on a biweekly schedule during the breeding season. The study is designed to monitor stork colonies with differences in nest numbers and densities, at interior freshwater and coastal marine-estuarine sites, and with latitudinal and longitudinal dispersal throughout Florida. Care is taken to reduce researcher’s effects on the breeding storks and other species of colonial water birds by minimizing nest monitoring during pair-formation and early egg-laying periods. Colonies also are visited during the cooler morning and late afternoon and no visits occurred during inclement weather. The time spent at each nest is further minimized by use of two people to observe and record data and map nest distribution. After the nestlings are three to four-weeks old, they are counted from a distance with binoculars to avoid pre-fledging of nestlings.
2003 Breeding Season
The average fledging rate (number of large, fully feathered birds attaining 7-8 weeks of age) of wood storks at 14 colonies in north and central Florida was 1.49 fledglings for each nest during the 2003 breeding season. For only successful nests (nests that fledged at least one stork), the average fledging rate was 2.15 fledglings per nest. About 70.8 percent of monitored nests fledged at least one bird.
Significant differences existed among colonies in the average fledging rate, which ranged from 0.21 to 2.21 fledglings a nest. A cluster of colonies in Pasco and Hillsborough counties (Cypress Creek north of Tampa and in New Port Richey) in the west-central region and the Jacksonville Zoo colony, located north of Jacksonville in the northeast region, exhibited the greatest fledging rates. Colonies that exhibited low fledging success appeared to be widely distributed in both north and central Florida. However, the two most northern and western colonies of Ochlockonee North and Chaires, found north of Tallahassee in Leon County, both exhibited below average fledging success.
Nest failures appeared to be evenly distributed during the breeding season among most colonies. However, there were three colonies that exhibited a sizable number of nests failures associated with severe weather (wind speeds exceeding 20 mph and rainfall exceeding one inch per hour) during a short interval. Chaires (prior to May 13), Dee Dot south of Jacksonville (prior to May 23), and Croom in Hernando County (prior to June 17) all experienced a large number of nests that either were abandoned or collapsed as evidenced by unattended nests, fallen nest structures, or dead nestlings under the nest trees. The low fledging rate at Devils Creek in Pasco County was the result of an apparent abandonment of all but two of the nests by parent birds.
The average fledging rate of wood storks at 19 colonies in north and central Florida was 1.53 fledglings per nest during the 2004 breeding season. For only successful nests, the average fledging rate was 2.07 fledglings at each nest. About 71.3 percent of monitored nests fledged at least one bird.
An examination of the distribution of the number of fledglings per nest provided additional insight into the fledging success within each colony. Jacksonville Zoo and Chaires exhibited high fledging rates due to low numbers of complete nest failures and above higher numbers of two-fledgling and three-fledgling nests. In contrast, Bird Island near Vero Beach, Lake Russell near Kissimmee, Little Gator Creek near Dade City, Matanzas Marsh near St. Augustine, and Pelican Island near Sebastian exhibited low fledging rates due to low numbers of two-fledgling and three-fledgling nests and high numbers of complete nest failures.
Jacksonville Zoo again possessed the greatest fledging rate in 2004. While several colonies rebounded and exhibited higher fledging rates (Chaires, Devils Creek), other colonies (Little Gator, Lake Russell, Matanzas Marsh) exhibited lower productivity in 2004 compared to 2003. Several stork colonies exhibited noticeably fewer nests in 2004 compared to 2003.
Pumpkin Hill north of Jacksonville had no nesting activity in 2004 compared to 2003, which had 120 nests. Colonies that possessed fewer nests in 2004 included Cypress Creek (175 nests in 2003; 59 in 2004), New Port Richey (225 nests in 2003; 178 in 2004), Lone Palm in Lakeland (175 nests in 2003; 82 in 2004), and Lake Rosalie near Lake Wales (125 nets in 2003; 46 in 2004).