The Everglades Handbook
Section 3: Birds
With close to 400 species of birds documented as occurring naturally in South Florida, the overall list of birds, or “avifauna,” is rich. Just under 300 species are considered to be of regular occurrence, other species being known from only a few records. About 60% of these species are winter residents, migrating into South Florida from the north, or are hurried visitors, stopping only briefly in the spring or fall in their migration between tropical America and points farther north in the United States or Canada. The remaining 40% are the species that breed in South Florida. The list of species of birds breeding in South Florida — about 116 species — is substantially smaller than lists for areas of similar size in the northeastern United States. Furthermore, not all of these South Florida breeders are year-round residents.
Breeding Land Birds
Just over 70 species of land birds breed in South Florida, half of which are songbirds or passerines.
Within the Florida peninsula, there is a pronounced decrease in the number of breeding passerine birds from north to south. Two South Florida examples are the prairie warbler, found in mangroves and other coastal communities (not prairies, despite the name), and the common yellowthroat, an Everglades marsh resident.
A common yellowthroat warbler. (Photo by Bob Branham).
In contrast to the geographic trend in land birds, more waterbird species occur in Florida than in states farther north. South Florida alone boasts 120 species, with 43 breeding in the region.
A large percentage of the waterbirds that breed in South Florida are also common to the West Indies, where substantially more waterbirds occur. Species that prefer shallow tidal habitats appear to treat South Florida just like another tropical island. Groups of the greater flamingo of the Caribbean region occasionally visit the shallows of Florida Bay (but many of the few flamingos seen in the past few decades are thought to have escaped from captivity). The reddish egret, found in the shallow estuarine and marine waters, and especially Florida Bay, also uses shallow tidal waters around the islands of the West Indies and Bahamas. The roseate spoonbill, which frequents similar habitats, moves about the region in an opposite pattern, with many individuals migrating northward from Cuba to southern Florida to breed during the winter months.
Pelagic, or open-ocean, seabirds also treat southern Florida like another Caribbean island. Examples that breed in the region include the magnificent frigatebird and two kinds of terns.
Two species of pelicans can be seen in southern Florida. The more common brown pelican breeds in Florida and is generally tropical. The American white pelican does not breed in southern Florida but winters here, commonly roosting on islands in Florida Bay.
The Anhinga is probably the most memorable waterbird seen in Everglades National Park. The most popular boardwalk viewing area, the Anhinga Trail, is its namesake.
Wading Birds and Feeding Habits
Of the three species that locate prey by touch, the wood stork commands respect as the true fisherman. Often foraging in cooperative groups, its technique, called tactolocation or groping, is to repeatedly probe its long, heavy, partially opened bill into shallow water, typically between 2 and 10 inches deep (Figure 20.2). If a living organism is detected by the highly sensitive receptors on the inside of the bill, the bill snaps shut by reflex action in less than 0.03 second. The specialized grope feeding behavior of the wood stork has rendered it endangered in the United States. It is highly dependent on a concentrated food source in shallow water. In years that lack dry weather, when water is kept too deep by artificial management, nesting failures result. Further, nesting also fails in years when the drydown conditions proceed so rapidly that the required food source is largely depleted before the wood story young are fledged. The entire reproductive period, from prenesting courtship until chicks are self-dependent, is 110–150 days, the longest of all Florida wading birds. An orderly sequence of dry-down in freshwater wetlands is the key to success and a probable cause of its demise in the modified Everglades. However, breeding populations of the wood stork have shown some recovery in the Everglades region, and improvement is expected with further restoration.
Photo by Bob Brahnam
The narrow, downward-curving beak of the white ibis (Figure 20.3) is an indicator that something is unique about its mode of feeding. In contrast to the wood stork’s slow, cautious approach, the white ibis rapidly probes the water—sometimes with its head briefly submerged—and explores in, around, and under obstacles as well as probing sediments (or soil on land). ibis. The decurved beak is advantageous for this probing technique. The rapid bobbing of the head and neck is easier with the beak aligned in the motion. The white ibis was historically the most abundant wading bird in South Florida, but its populations declined precipitously in the 1980s. Beginning in 2003, however, nesting success has increased considerably.
Photo by Tom Lodge
The dark-colored glossy ibis, which is more common farther north in Florida and along the Atlantic coast. Its populations fluctuate in southern Florida, but it now more frequently visits Everglades National Park. The glossy ibis is locally abundant and its populations have been expanding since it first started breeding in Florida in the 1880s. It now breeds in the Everglades in small numbers.
Photo by Bob Brahnam
The spoonbill’s normal feeding behavior is to swing its mostly submerged, opened, spoon shaped bill in a wide arc from side to side as the bird walks about in shallow water to catch small fish and invertebrates. When several birds are present, they often team up, forming a line. Spoonbills nest primarily on mangrove islands in Florida Bay, but normally fly to brackish wetlands of the mainland to feed. There, adequate seasonally changing flows of fresh water into headwater creeks have been shown to be critical to the spoonbill’s food supply. The juvenile birds are very pale (almost white) and obtain their adult pink color by extraction of a red carotenoid pigment from crustaceans in their diet, the same pigment group also deposited in the greater flamingo’s feathers.
Great Blue Heron
The technique of spearing fish from 3 to 12 inches long is common for great blues, which are most abundant in southern Florida in winter when migratory individuals join the resident population, in both interior freshwater wetlands and in saline coastal habitats. This species objects to the close presence of other members of its species, tending to feed alone. Aided by its large size, the great blue heron often fishes in water up to about 2 feet, which is much deeper than for other herons except the closely related great white heron. If attracted by abundant prey, great blues will even swim, like ducks, in water too deep to touch bottom.
Great White Heron
The great white heron is almost completely confined to saline habitats of southern Florida and the West Indies. It is seen often, usually standing alone in the shallows of Florida Bay. Its habitat specialization makes its niche quite different from the niche of the more ubiquitous great blue. During spring, juvenile and some adult great white herons may move northward from Florida Bay into the freshwater Everglades.
Formerly called the Louisiana heron, this species ranges widely over the Caribbean region, throughout Florida, and into closely neighboring areas of the southeast. Farther north it is most common in saline tidal areas, but in Florida it also frequents freshwater wetlands. Compared with the great blue heron, this smaller, beautifully colored species is a restless and agile athlete, actively running after the 1–2-inch fish that form the bulk of its diet. Its preferred habitat is a wide expanse of very shallow water; probably 2–5 inches deep being optimal for its highly active style. The exquisitely colored breeding adults, with blue beaks and dark, ruby-red eyes, are the most striking in appearance among southern Florida’s herons and egrets.
Slightly larger than the tricolored heron, the reddish egret is a specialist of shallow marine flats at low tide and is seldom found inland. It comes in two color phases: a rusty-brown head and neck with a slate-gray body that is similar to the smaller little blue heron, and a white form that can be confused with the smaller snowy egret and immature little blue heron. The antics of this highly active species include the athletic ability of the tricolored heron in addition to the regular use of wings as a sun visor for shading and maneuvering. The reddish egret’s decorative feathers brought it closer to extinction by plume hunters than any other species. Its recovery since the early 1900s has been very slow.
“Great patient egret” would be a more descriptive name for this species. Periods of nearly motionless stance followed by a slow, careful walk describe its normal style. It prefers to feed alone in open marsh habitat. However, in times when food is concentrated into pools by low water, it will feed near others of its own species as well as other kinds of wading birds. Its posture of leaning far forward, with neck outstretched and head held horizontally rather than pointed downward like most herons, is typical. In final efforts of locating prey, it is apt to move its head from side to side, as if to enhance its depth perception.
What the snowy lacks in size, this smaller heron offsets by aggressive feeding. Yellow slippers and fast footwork are the trademarks of this gregarious species, which is commonly seen feeding in flocks with various other species. Its behavior varies more than any of its competitors. When wading in shallow water, this swiftly reacting bird often uses its feet in creative ways: stamping, stirring, and probing to flush out potential prey, or even chattering its bill in the water. Some of these actions attract its principal food, the mosquitofish, an inch-long species that is apt to investigate disturbances in seeking its own food. As anyone can see, the snowy egret sports beautiful plumes in the breeding season and was another target of plume hunters. Like the great egret, its numbers were decimated in the early 1900s, but it recovered well.
Little Blue Heron
The most characteristic feeding behavior of the little blue can be described as meticulous investigation. This species is most at home along wetland edges, where it walks very cautiously and carefully, examining any obstacles such as stones, plants, and logs. The little blue’s preferred techniques give it a strikingly different diet than the previously described species. Small frogs and polliwogs, insects, grass shrimp, crayfish, spiders, and other invertebrates form a much larger proportion of its diet than is normal for the other herons and egrets.
Found in numerous color varieties throughout the world’s temperate and tropical climates, green herons are most at home perched on rocks, roots, or tree branches, waiting for prey to come within reach. They seldom wade, but will stand quietly in very shallow water in protected areas. When potential prey comes within range, this little predator may begin to stretch out, with neck and legs extended, in anticipation of striking, and may even leap from its perch into the water. This species is one of the few in the heron/egret group that prospers in years when no pronounced drydown occurs. Some individuals learn to attract prey with bits of food. This phenomenon has been observed where fish food is available, such as in zoos and outdoor public aquariums.
Black-Crowned Night-Heron and Yellow-Crowned Night-Heron
Night-herons, which are common in southern Florida, are specialists at nocturnal feeding and are seldom seen in daytime feeding groups of the other wading birds. Both species have large eyes, which are a beautiful deep red in adults.
Threatened and Endangered Birds
Several Everglades birds are listed as threatened or endangered under Florida and/or federal regulations. Prominent issues in the management of the Everglades have focused on three endangered birds: the wood stork, the snail kite, and the Cape Sable seaside sparrow.
The snail kite is related to hawks and eagles, and is about the same size and shape as the commonly seen red-shouldered hawk. It differs from the hawk in that it is generally dark brown (female) or slate black (male). While the species is also found in Cuba and Central and South America, our population is a subspecies that only occurs in southern Florida, isolated from the other populations because it does not migrate.
The beak of the snail kite is a narrow curved hook. This adaptation allows it to eat its primary food, the applesnail, which it snatches in its talons from the water while hovering. The specialized diet renders the snail kite extremely habitat-specific to shallow, long hydroperiod marshes that contain sufficient applesnail populations, where the snails are visible and the water surface is not obstructed by dense vegetation such as cattails.
Cape Sable Seaside Sparrow
The Cape Sable seaside sparrow (CSSS is its common acronym), named for its former occurrence in salt marshes on Cape Sable. It is nonmigratory and endemic to the extreme South Florida mainland where its current restriction to freshwater wetlands is unusual for the species. The CSSS attracted attention when a population monitored between the 1950s and 1970s decreased by an estimated 95%. The entire range of the CSSS is within Everglades National Park and the southern Big Cypress National Preserve, the most restricted range of any North American bird. It is now confined to areas of marl prairie habitat dominated by muhly grass on both sides of the Shark River Slough, where six subpopulations, designated “A” through “F,” have been monitored since 1981.
The CSSS’ highly sedentary lifestyle is sensitive to fire, water levels, and nest predation, especially by rice rats and fish crows. Avoiding dense sawgrass habitat, the birds construct nests close to the ground in the sturdy bases of muhly grass tussocks during the dry season. Accordingly, flooding deeper than about 4 inches during the breeding period has been shown to inhibit nesting or cause nest abandonment.
Cape Sable seaside sparrow subpopulations. Only subpopulation A, now with very few birds, is not designated as critical habitat. Courtesy of Robert A. Johnson and Caryl Alarcon, Everglades National Park.