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Potentially Misidentified Species:
From a distance, A. ajaia can
be confused with the greater flamingo, Phoenicopterus ruber, due to the
similarity of body color in both species. However, the roseate spoonbill is
generally smaller than the flamingo, with a shorter neck, and a longer,
spoon-shaped bill.
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
A. ajaia occurs from southeastern Georgia and Florida through the
Gulf of Mexico, south to Argentina (Le Grand 1980; Robertson et al. 1983), with
Cuba potentially being an area that acts as a source population for some
sub-adult birds that eventually arrive in Florida Bay (Allen 1942; Robertson
1983). The Florida population is distinctive from the Texas and Louisiana
populations.
IRL Distribution:
A. ajaia occurs lagoon-wide, but is most common in the estuaries
surrounding the Cape Canaveral area.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
The roseate spoonbill, Ajaia ajaia, grows to a height of
approximately 32 inches (81 cm), with a wingspan of 53 inches (1.3 m) (Farrand
1988).
Abundance:
The breeding population of the roseate spoonbill in Florida numbered as few
as 30 pairs in 1942 (Allen 1942). The species was nearly extirpated from Florida
and Texas from the late 1800s through the mid-1930s (Powell et al. 1989) due to
the impacts of human harvesting for both food and feathers for the millinery
trade. Following protection efforts, spoonbills reestablished small populations
that grew quickly. By 1978, the Florida population had increased to
approximately 1400 pairs (Robertson et al. 1983). However, later surveys (Powell
et al. 1989) reported the number of breeding pairs in Florida Bay to be 400-450,
and a recent Everglades National Park publication estimates only 100 - 200
breeding pairs in Florida Bay. In Texas, a 1979 survey estimated the number of
breeding pairs at 2,500 (Blacklock et al. 1979).
Reproduction:
In some areas, the breeding season of A.
ajaia is somewhat influenced by local rainfall patterns (Leber 1980). In a
Costa Rican study, for example, Leber (1980) observed that both roseate spoonbills and
wood storks nest
during months when rainfall totals begin to decrease. Kahl (1964) suggested this
pattern may be related to the increase of food availability to both adults and
chicks as water levels in estuaries decrease throughout the dry season. In
Florida, spoonbills commonly nest among several other species of wading birds.
Spoonbills arrive in the nesting colony between October and December (Leber 1980;
Robertson et al 1983) and leave the area by late March or April (Roberston
1983), with nesting having no apparent correlation to rainfall patterns. In
Texas, breeding adults begin to congregate in mid-March. Pairing begins by
mid-April, and nesting by late April or early May. Egg laying generally occurs
in mid-May.
In Costa Rica, spoonbill nest density in a
mixed colony was approximately 2.2 nests per square meter in the preferred core
area of the colony, versus only 0.8 nests per square meter at the periphery of
the colony (Leber 1980). Nests are built in mangroves or other available trees
and shrubs, and are usually located within 1 meter of the main trunk of the
tree. Nest height averages approximately 2.7 m above the ground in Costa Rica (Leber
1980), while those in Texas were observed at lower heights, primarily within 1
meter of the ground (White et al. 1982). Nests are often concealed by overhead
vegetation (Leber 1980) and are constructed of plant material that is abundant
near the nest site. Dead twigs form a platform approximately 0.5 m in width upon
which live and dead stems of other vegetation are laid to a depth of
approximately 6 cm (White et al. 1982). Activities of the nesting pair
eventually form a shallow depression in the nest into which the female lays its
eggs.
Clutch size in Florida populations of A.
ajaia averages between 1.9 - 3.3 eggs per clutch (Leber 1980), while in the
Texas population, 2 - 4 eggs per clutch is common (White et al. 1982).
Eggs are incubated 22 - 23 days, and young fledge between 35 - 42 days.
One brood per year is produced.
Nest success
in spoonbills is known to vary from year to year depending upon
environmental conditions. No figures are available for hatching success in
Florida; however, in Costa Rica, hatching success averages approximately 74%,
among the highest rates for large wading birds. In Texas, hatching success has
averaged 73%, with nest success as high as 87% (White et al. 1982). Much of the mortality among
eggs is accounted for by failure of the eggs to hatch, and to death within the
first 2 weeks of life (Rodgers 1980; White et al. 1982). Adults startled from
nests can often brush or kick eggs and chicks out of the nest. Allen (1942)
observed that spoonbills were highly sensitive to disturbances around the nest
site, with frequent disturbance sometimes leading to a complete disruption of
the breeding cycle and abandonment of the nest. Additionally, snakes and avian
predators such as vultures and even pelicans have been observed preying upon
both eggs and chicks. White et al. (1982) observed that the mortality rate among
nestlings in Texas averaged 32% over 3 years, with most nestlings lost within 2
weeks of hatching. They estimated that half of the chicks were lost to
predators, or to other unobserved causes, while half were found dead in or near
the nest.
Embryology:
The incubation period in Ajaia ajaia
lasts 22-24 days, with adult females laying one egg every other day (Allen 1942;
White et al. 1982). Eggs hatch in the order in which they were laid, with chicks
hatching every other day (White et al. 1982). At hatching, chicks weigh
approximately 50 g, and tend to gain an additional 9 g over the next several
days. After about day 4, however, they rapidly gain weight; and by day 16 they
achieve approximately half adult weight (White et al. 1982).
Chicks fledge at approximately 6 weeks of age,
and by early July, the young hatched in late April are able to fly several
hundred meters under their own power. Birds begin to disperse from the nesting
area by early August, with few remaining at the end of September (White et al.
1982).
The skin, jaws and legs of newly hatched
chicks are a uniform pink color, the feather tracts covered by thick white down
that dries and becomes fluffy within 12 hours after hatching. 2 days after
hatching, the eyes open. Feather development begins with the emergence of the
feather sheaths of the flight feathers at about day 5. The rest of the body
remains covered in down for approximately 3 weeks, and at this time the feather
sheaths of the other major feathers begins to emerge. Feather growth takes 3
weeks to complete, with full development being complete 42 days after hatching
(White et al. 1982). By this time, they young are fully capable of flight and
are thus considered fledged. Full adult plumage does not appear until juveniles
are approximately 3 years old, but there is significant variation among
individuals (White et al. 1982).
Interestingly, bill morphology of hatchlings
is not the characteristic spoon-shaped bill found in adults (White et al. 1982).
Rather, young chicks have short, soft bills that are somewhat leathery. The bill
tip begins to widen at 9 days of age, and by 16 days, it takes on the shape of
the adult bill, and continues to lengthen as the chick ages.
Organochlorides
such as DDE and PCBs have been shown to be the primary pollutants
which occur in A. ajaia eggs. White et al. (1982) found DDE
present in all eggs analyzed, while PCBs were present in 90% of
samples. Generally, organochloride levels tended to be under 2 ppm,
though some spoonbill eggs contained more than 15 ppm. Eggshell
thickness was shown to be approximately 5% thinner than in the pre-DDT
age, but no biological significance was assigned to this finding,
as it was determined that the percentage difference was within the
range of intraclutch variation (White et al. 1982). Spoonbills appear
to be somewhat less sensitive to organochloride pollution that certain
other species such as the brown pelican. Pelicans suffer nest failure
when eggs contain a concentration of DDE greater than 2.5 ppm. While
over 30% of the eggs in the White et al. (1982) study had DDE levels
higher than 2.5 ppm, and some eggshell thinning was detected, no
population declines or major reproductive failures were observed.
V. COMMUNITY ECOLOGY
Trophic Mode:
A. ajaia is a heterotroph that feeds on small fishes, shrimps, crabs
and other epibenthic and benthic species. It feeds by moving its bill slowly
through the water as it wades, straining out food items, and occasionally
snapping its bill closed upon detecting larger prey (Farrand 1988).
Associated Species:
A. ajaia is found nesting with wood storks
(Mycteria
americana)(Leber 1980), great egrets (Casmerodius albus), great blue
herons (Ardea herodias), snowy egrets (Egretta thula), cattle
egrets (Bubulcus ibis), tricolored herons (Hydranassa tricolor),
black crowned night herons (Nycticorax nycticorax), and laughing gulls (Laras
atricilla).
VI. SPECIAL STATUS
Special Status:
This species is
not federally listed as threatened or endangered, but in Florida,
is considered a Species of Special Concern (SSC).
During the late 1800s, roseate spoonbill populations
from Florida through Texas were nearly extirpated due to trappers
and hunters who killed the birds and collected their feathers for
the fashion industry. By the 1940s, Allen (1942) reported
that the breeding population of spoonbills in Florida may have numbered
as few as 30 nesting pairs. Protection efforts after that time aided
the birds in reestablishing nesting colonies, and by the late 1970s,
the Florida population was estimated to be approximately 1,400 breeding
pairs (Robertson et al. 1983).
Today, habitat loss and degradation of forging
and nesting habitats are the primary conservation concerns for roseate
spoonbills in the United States (Powell and Bjork 1989, Martin 1991,
Bjork and Powell 1996, Gawlik et al. 1998). In Florida, many nesting
sites are already protected as part of the State and National park
systems (Everglades National Park, Tampa Bay Sanctuaries, Merritt
Island National Wildlife Refuge, etc.) but foraging habitat remains
vulnerable to human development and disturbance (Bjork and Powell
1996). Spoonbills have a preference for their feeding locations
to be close to colony sites; thus, loss of foraging habitat could
cause shifts in breeding locations. Evidence from the Florida Keys
shows that loss of spoonbill feeding areas due to development from
1955 – 1985, likely caused breeding sites to be moved from the southeastern
region of Florida Bay to more northern areas as mangrove habitats
were eliminated (Powell et al. 1989; Bjork and Powell 1994). In
Texas, Gawlik et al. (1998) reported that serious population decreases
of nesting spoonbills in the Galveston Bay Estuary were concurrent
with the loss of feeding grounds on coastal marshes.
Since 1979, the roseate spoonbill has been
listed by the State of Florida as a Species of Special Concern.
Prior to 1972, it was listed in Florida as Endangered, but was downlisted
to Special Concern status when the category was first adopted (Bjork
and Powell 1996). With the designation of Special Concern status
in Florida, it is recognized that roseate spoonbills are vulnerable
to habitat alteration or destruction, and are negatively impacted
by human disturbance. Spoonbills are also classified as Rare by
the Florida Committee on Rare and Endangered Birds and Animals (Bjork
and Powell 1996).
Throughout Florida (Bjork and Powell 1994,
1996, Smith and Breininger 1995), multi-species protection efforts
are being undertaken to conserve existing populations of wading
birds, and to promote their future growth. Habitat protection measures
are effected through both land acquisition programs and ecosystem
restoration efforts. In south Florida, for example, approximately
50% of the remaining mainland mangrove area east of U.S. Highway
has been purchased by the South Florida Water Management District
and Miami-Dade County (Dumas 2000), with ongoing acquisitions attempting
to secure the remaining mainland mangrove areas.
Ecosystem restoration efforts are also underway
as the importance of natural water flows and water level fluctuations
are increasingly recognized. The Comprehensive Everglades Restoration
Plan, delivered to Congress in July 1999, is currently being implemented.
This plan includes restoring the hydrology of all major estuaries
from Caloosahatchee River on the Gulf Coast to St. Lucie Estuary
on the Atlantic Coast, based on a hydrology model that mimics pre-drainage
conditions for salinity, freshwater flow volumes and timing, duration
of flooding, and depth of water (Dumas 2000). At Kennedy Space Center,
mosquito impoundments are being managed to maintain favorable water
levels and salinities for wading bird foraging and nesting (Smith
and Breininger 1995).
Spoonbill and other wading bird populations
will continue to be monitored to determine whether further protections
are necessary. Spoonbills in Florida Bay may be a key indicator
species of ecosystem health, and long-term changes in their population
sizes, annual reproductive success, and colony distribution patterns
are expected to show how effective regional restoration efforts
have been.
Benefit in the IRL:
Aesthetic, ecological.
Economic
Importance:
None. A.
ajaia was formerly hunted both for its colorful plumage, and
to a lesser degree, for food. Today, however, it has no direct
economic importance.
VII. Bibliography
Allen, R.P. 1942. The Roseate
Spoonbill. Research Report No. 2, National
Audubon Society, New York, NY.
Amos, W. and S. Amos. 1997. Atlantic
and Gulf Coasts. Alfred A. Knopf,
Inc. New York, NY. 672
pgs.
Bjork, R. D., G. V. N. Powell. 1994. Relationships
between hydrologic
conditions and quality and quantity of
foraging habitat for Roseate Spoonbills
and other wading birds in the C-111 Basin.
South Florida Res. Center,
Everglades Natl. Park, Natl. Park Serv.,
Final Rep., Homestead, FL.
Bjork, R., G. V. N. Powell. 1996. Roseate Spoonbill.
Pp. 295–308 in Rare and
endangered biota of Florida. Vol. 5 (J. A.
Rodgers, H. W. Kale, and H. T.
Smith, eds.). Univ. Press of Florida, Gainesville.
Blacklock, G.W., R.D. Slack, D.R. Blankenship,
et al. 1979. Texas Colonial
Waterbird Census. Proc. 1st Welder
Wildl. Found. Symp.:252-259.
Dumas, J. V. 2000. Roseate Spoonbill (Ajaia
ajaja). In The Birds of North
America, No. 490 (A. Poole and F. Gill,
eds.). The Birds of North America,
Inc., Philadelphia, PA.
Dunstan, F.M. 1976. Roseate Spoonbill Nesting in Tampa Bay, Florida.
Florida
Field Naturalist 4(2):25-27.
Farrand Jr., J. 1988. An Audubon
Handbook: Eastern Birds. McGraw-Hill
Book Co. New York, NY. 496 pgs.
Kahl, M.P., Jr. 1964. Food Ecology
of the Wood Stork (Mycteria Americana)
in Florida. Ecol. Monogr.
34(2):97-117.
Le Grande, H.E., Jr. 1980. Southern
Atlantic Coast Region. American Birds
34:149-152.
Gawlik, D. E., R. D. Slack, J. A. Thomas,
D. N. Harpole. 1998. Long-term
trends in population and community measures
of colonial nesting waterbirds
in the Galveston Bay Estuary. Colon. Waterbirds
21: 143–151.
Leber, K.K. 1980. Habitat Utilization in
a Tropical Heronry. Brenesia 17:97-136.
Martin, R.. 1991. Regional overview of wading birds
in Louisiana, Mississippi
and Alabama. Pp. 22–33 in Proceedings of
the Coastal Nongame Workshop,
U.S. Fish Wildl. Serv., Florida Game and
Fresh Water Fish Commision
(D. P. Jennings,
comp.). U.S. Fish Wildl. Serv., Fort Collins, CO.
Powell, G. V. N., R. D. Bjork.
1989. Relationships between hydrologic
conditions and quality and quantity of
foraging habitat for Roseate Spoonbills
and other wading birds in the C-111 Basin.
South Florida Res. Center,
Everglades Natl. Park, Natl. Park Serv.,
Annual Rep., Homestead, FL.
Powell, G. V. N., R. D. Bjork. 1990. Relationships
between hydrologic
conditions and quality and quantity of
foraging habitat for Roseate Spoonbills
and other wading birds in the C-111 Basin.
South Florida Res. Center,
Everglades Natl. Park, Natl. Park Serv.,
Second Annual Rep., Homestead,
FL.
Powell, G. V. N., R. D. Bjork. 1991. Relationships
between hydrologic
conditions and quality and quantity of
foraging habitat for Roseate Spoonbills
and other wading birds in the C-111 Basin.
South Florida Res. Center,
Everglades Natl. Park, Natl. Park Serv.,
Third Annual Rep., Homestead,
FL.
Powell, G. V., R. D. Bjork, J.
C. Ogden, R. T. Paul, A. H. Powell, W. B.
Robertson. 1989. Population trends in some
Florida Bay wading birds.
Wilson Bull. 101: 436–457.
Robertson, W.B., Jr., L.L. Breen,
et al. 1983. Movement of Marked Roseate
Spoonbills in Florida With
a Review of Present Distribution. Journal of Field
Ornithology 54(3):225-352.
Rogers, J.A., Jr. 1980.
Reproductive Success of Three Heron Species on the
West Coast of Florida.
Florida Field Naturalist 8:37-40.
Robertson, W. B., L. L. Breen,
B. W. Patty. 1983. Movement of marked
Roseate spoonbills in Florida with a review
of present distribution. J. Field
Ornithol. 54: 225–236.
Smith, R. B., D. R. Breininger. 1995. Wading
bird populations of the Kennedy
Space Center. Bull. Marine Sci. 57: 230–236.
Smith, R. B., D. R. Breininger. 1988. Northern breeding range extension
for the Roseate Spoonbill in Florida. Fla.
Field. Nat. 16: 65–67.
White, D.H., C.A. Mitchell,
et al. 1982. Nesting Ecology of Roseate Spoonbills
at Nueces Bay, Texas. The Auk
99:275-284.
Report by:
K. Hill, Smithsonian Marine Station
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Page last updated: June 21, 2006
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