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.
CURRENT FWC
PROJECT
The current Florida Fish and Wildlife Conservation Commission's
(FWC) research project is entitled "Productivity of Wood Storks
Mycteria americana in North and Central Florida." The
primary participants are James A. Rodgers and Steve Schwikert
working out of the Gainesville Wildlife Research Laboratory.
Rodgers and Schwikert are assisted by numerous volunteers and
cooperators working around the state.
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.
Study methods
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.
Results of the 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.
An examination of the distribution of the number of fledglings
per nest provided more insight into the fledging success within
each colony. Cypress Creek and Jacksonville Zoo exhibited high
fledging rates due to low numbers of complete nest failures (which
means no fledglings) and high numbers of three-fledgling nests. In
contrast, Chaires exhibited a low fledging rate due to low numbers
of two-fledgling and three-fledgling nests and high numbers of
complete nest failures.
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.
Results of the 2004 Breeding Season
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.
Significant differences in the average fledging rate existed
among colonies (range=0.25 to 2.37 fledglings per nest) during
2004. Colonies exhibiting higher or lower fledging rates again
appeared to be evenly distributed across north and central
Florida.
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).
Results of the 2005 Breeding Season
The average fledging rate of wood storks at 22 colonies in north
and central Florida during 2005 was 0.49 fledgling per nest. For
only successful nests (a successful nest is one that produces at
least one stork), the average fledging rate was 1.88 fledglings for
each nest. Only about 42.3 percent of monitored nests fledged at
least one bird. Significant differences in the mean fledging rate
existed among colonies (range=0 to 2.40 fledglings a nest) during
2005. Colonies exhibiting higher fledging rates were concentrated
in the northeast regions of the state (Jacksonville Zoo, Dee Dot,
Pumpkin Hill) and northwest (Chaires, Ochlockonee North,
Ochlockonee South). Whereas, colonies possessing lower fledging
rates appeared to be evenly distributed across north and central
Florida, three of four colonies monitored in the southeast region
were at or below this index.
Several unusual events occurred during the 2005 nesting season.
Storks started nesting at Little Gator Creek in Pasco County but
abandoned the 12-15 nest starts and the entire breeding season
prior to mid-March. Storks abandoned 10-12 nest starts at
Ochlockonee South, located north of Tallahassee about mid-March,
began renesting in early April, and exhibited a partial abandonment
prior to mid-June. About 80 of 154 monitored nests (51.9 percent)
at Croom were abandoned prior to mid-May. Storks abandoned 41 of 42
nests (97.6 percent) at Matanzas prior in late-June. All 29 nests
at Pelican Island were abandoned. Finally, no storks nested at
Devils Creek. An examination of the distribution of the number of
fledglings per nest provided further insight into the fledging
success within each colony. Jacksonville Zoo, Chaires, Ochlockonee
North, and Dee Dot exhibited high fledging rates due to below
average number of complete nest failures (or no fledglings) and
above average number of two-fledgling and/or three-fledgling nests.
In contrast, Bird Island, Lone Palm, Deseret Ranch near Holopaw,
Matanzas Marsh, and Pelican Island exhibited low fledging rates due
to below average number of two-fledgling and three-fledgling nests
and above average number of complete nest failures. The one bright
spot in the 2005 nesting season was the renesting of storks at
Pumpkin Hill after no nesting in 2004.
The 2005 nesting season followed an above average year of
rainfall and hurricane activity. Storm damage to nesting trees may
have precluded storks nesting at Devils Creek. Inclement weather
resulted in the eventual collapse during the nesting season of a
cypress tree and contributed in large part to the overall low
productivity rate at Lake Rosalie. The elevated water levels at
these interior freshwater sites in 2005 would not directly disrupt
nesting within the colony as occurred at Little Gator Creek and
Ochlockonee South, and partial abandonment as occurred at Matanzas
and Croom. Rainfall also did not directly affect the nesting
failure at the marine estuarine site of Pelican Island. However,
large amounts of rainfall and the elevated water levels associated
with the foraging sites around a colony are suspected to cause the
over-dispersal of aquatic freshwater prey and result in
non-breeding or abandonment of nesting by storks.
Results of the 2006 Breeding Season
In a slightly modified area of coverage, the average fledging
rate of wood storks within north and central Florida during 2006
was 2.25 fledglings/nest (n=889 nests at nine colonies). For only
successful nests (fledged at least one stork), the average rate was
2.59 fledglings/nest (n=776 nests). About 87.9 percent of monitored
nests fledged at least one bird and 83.4 percent of nests fledged
2+ birds. Significant differences in the mean fledging rate
(range=0 to 2.59 fledglings/nest) existed among colonies. Differing
rates among colonies were due to different frequencies of complete
nest failures (no fledglings) and nests with two fledglings and/or
three-fledglings. The three highest fledging rates were at colonies
along the southeastern coastal region of the district, whereas the
three lowest fledging rates occurred in the northeast part of the
state. Water levels were generally lower during the 2006 nesting
season due in part to the low rainfall during 2005-2006. Most stork
colonies exhibited their greatest fledging rates in 2006 compared
to previous years. However, lack of flooded nest trees resulted in
the lack of breeding storks at the Pumpkin Hill colony. The failure
of most nests at Matanzas Marsh was associated with low water
levels and depredation, or plundering, of nests by raccoons.
Results of the 2007 Breeding Season
The average fledging rate of wood storks within north and
central Florida during 2007 was 0.71 fledgling/nest (n=186 nests at
six colonies). Only about 50.0 percent of monitored nests fledged
at least one bird and only 31.1 percent of nests fledged more than
two birds. Significant differences in the mean fledging rate
existed among colonies (range=0.27 to 1.45 fledglings/nest) during
2007. There also were fewer nests recorded at these six active
colonies in 2007 compared to all previous years. Six other colonies
active 2006 contained no stork nests in 2007. The reason for lack
of nesting at three of these colonies probably was due to little or
no water present under the nest trees (primarily cypress trees)
prior to the nesting season. The reason for no nesting at the other
sites is unclear but these colonies have exhibited a continued
decrease in nest numbers during recent years. A comparison of the
combined fledging rate for all colonies within the north and
central Florida region indicates the rate in 2007 was the second
lowest fledging rate recorded during the past four nesting seasons
of this study.
Results of the 2008 Breeding Season
The average fledging rate of wood storks (Mycteria
americana) within the St. Johns River Water Management
District (SJRWMD) of north and central Florida during 2008 was 1.51
fledglings/nest (n=419 nests at six colonies). About 72.3 percent
of nests fledged at least one bird and 60.8 percent of nests
fledged more than two birds. Significant differences in the mean
fledging rate existed among colonies (range=1.02 to 2.13
fledglings/nest) during 2008. There were more nests per colony and
higher fledging rates at these six active colonies in 2008 compared
to 2007. Three other colonies active in previous years were not
active in 2008. The reason for no nesting at these sites is unclear
but may be due to no water present under the nest trees prior to
the nesting season or little flooded foraging habitat. These
colonies have exhibited a continued decrease in nest numbers during
recent years. A comparison of the combined fledging rate for all
colonies within the SJRWMD region of Florida indicates the fledging
rate in 2008 was in the middle of the range of fledging rates
recorded during the past five nesting seasons.
Annual number of wood stork nests recorded at colonies
in the SJRWMD region of North and Central Florida. Colony
abbreviations are as follows: PH=Pumpkin Hill, JZ=Jacksonville Zoo,
DD=Dee Dot, MM=Matanzas Marsh, LD=Lake Disston, HO=Hontoon Island,
HI=Horseshoe Island, DR=Deseret Ranch, KR=Kemper Ranch US192S,
PI=Pelican Island, NF=North Fork, and BI=Bird Island.
Acknowledgments
This project is a cooperative effort among numerous agencies and
individuals including Gabrielle A. Griffin (Florida Institute of
Technology), Donna Bear-Hull (Jacksonville Zoological Gardens),
Bill Brooks (U.S. Fish and Wildlife Service), Paul Elliot
(Southwest Florida Water Management District), Gian Basili and
Becky Trudeau (St. Johns River Water Management District), J. B.
Miller (Florida Department of Environmental Protection), Kristin
Ebersol (Florida Department of Environmental Protection), and Amy
Kalmbacher (Florida Department of Environmental Protection). We
also wish to thank those individuals, organizations, and agencies
that allowed us access to the colonies on their properties or under
their jurisdiction: Dee Dot (Keith Kelly and Dee Dot Timberlands,
Inc.), Croom (Vincent Morris and Florida Forest Service), New Port
Richey (Al Lolli and Ken Tracy), Lake Rosalie (Bob Armington and
the Armington family), Lake Russell (Sandy Woiak and The Nature
Conservancy), Cypress Creek (Jill Lehman and Hillsborough County
Parks and Recreation), and Lone Palm (Joe Hodge, Lone Palm Golf
Club). Numerous other individuals assisted in the collection of
data, especially Bill Brooks, Bert Charest, J.B. Miller and LeAnn
White. Funding was provided in part by grants from the U.S. Fish
and Wildlife Service in the Jacksonville Field Office and the St.
Johns River Water Management District in Palatka.
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