Article below courtesy of Grant C. Sizemore, Martin B. Main, and Elise V. Pearlstine2 University of Florida IFAS Extension
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Wading birds are considered by many to be the most majestic of all of Florida's birds. Their long necks and graceful poses make these birds distinctly appealing. Although they come in a variety of shapes and sizes, wading birds are generally long-legged, carnivorous, and can be found in or around water. These large-bodied and colorful birds are a favorite among serious birders and casual observers alike.
Wading birds live throughout Florida and make up an integral part of the natural landscape, especially in south Florida where they often form large, multispecies feeding aggregations and nest and roost in large colonies. In addition to being enjoyable to observe, wading birds also play key ecological roles in their respective habitats. Wading birds are top predators in their systems and also function as indicators of ecosystem health (Powell and Powell 1986, Kushlan 1993, Main and Vavrina 2001). Many wading bird species are similar in appearance and yet information about their distinct characteristics and behaviors can aid in identification. Learning to identify species can increase enjoyment of wading birds, whether they are in a back yard, a neighborhood park, or the large expanses of wetlands that make up the Everglades ecosystem.
Taxonomy and Status
Florida's wading birds include 15 native species representing three families, all of which belong to the order Ciconiiformes (Table 1). These families are Ardeidae, Threskiornithidae, and Ciconiidae. The family Ardeidae is by far the most numerous and includes herons, egrets, and bitterns. In Florida, the family Threskiornithidae encompasses two species of ibis and the Roseate Spoonbill (Platalea ajaja). The family Ciconiidae includes the Wood Stork (Mycteria americana).
Several species of wading birds found in Florida are non-native or recent arrivals; these are the Sacred Ibis (Threskiornis aethiopicus), Scarlet Ibis (Eudocimus ruber), and Cattle Egret (Bubulcus ibis). Although a member of order Ciconiiformes, the Cattle Egret is primarily a terrestrial bird often found around livestock and farm machinery where it watches for insects and small prey that might be flushed and make an easy meal. This species is thought to have arrived in Florida via natural range expansion. Unlike the Cattle Egret, the two ibises are wetland birds. Although the Scarlet Ibis may occasionally breed in Florida, the Sacred Ibis and Scarlet Ibis are not as abundant as Cattle Egrets and are typically only seen in southern Florida. These two ibises are accidentals, non-native species that have not become established.
Cranes and Flamingos
Within Florida there are four particular species that look similar but are unrelated to wading birds of the order Ciconiiformes. These species are the Sandhill Crane (Grus canadensis), endangered Whooping Crane (Grus americana), Limpkin (Aramus guarauna), and Greater Flamingo (Phoenicopterus ruber).
The Sandhill Crane, Whooping Crane, and Limpkin are in the order Gruiformes. The two cranes are in the family Gruidae, and the Limpkin is in the family Aramidae. These three species have long legs, a long bill, and an elongated neck similar to wading birds. Although they do require wetlands for nesting and migration, Sandhill Cranes are primarily terrestrial birds common to prairies and pastures. Unlike wading birds, Sandhill Cranes consume a varied diet that includes seeds and plants and do not nest in colonies. Whooping Cranes and Limpkins live in freswater marshes and prairies. Whooping Cranes, recently reintroduced to Florida, consume a diet that includes grains, invertebrates and vertebrates. Limpkins specialized on snails and mussels. While Sandhill Cranes are generally gray and rusty in coloration, Whooping Cranes are strikingly white with red on the head. Limpkins are brown all over except for streaks of white, which are especially prominent on the head and neck.
The Greater Flamingo is a member of the order Phoenicopteriformes and in the family Phoenicopteridae. This species consumes mostly crustaceans, diatoms, mollusks, and algae. The Greater Flamingos seen in south Florida are either birds that have escaped from captivity or occasional visitors from the Caribbean. Greater Flamingos may be confused with the Roseate Spoonbill for a variety of reasons. Both species have relatively long legs, long necks, and pinkish plumage. Both also sift through the water with their bills when feeding. Depsite these similarities, the two species are unrelated. The easiest ways to tell the two species apart are by the dark outer wing feathers (primaries) on the flamingo and both species' distinctive bill shapes (see Roseate Spoonbill in Table 2).
Wading Bird Identification
Many of the wading birds are large and colorful, which makes them relatively easy to identify. However, it is still helpful to learn the distinguishing features to correctly differentiate between the various species. There are several key characteristics that can be used for easy identification: body size, plumage, and bill and leg color. Table 2 identifies these characteristics for adult wading birds found in Florida.
Wading bird feeding behavior includes a variety of strategies and behaviors, and no species is limited to just one strategy. There are two basic categories of feeding behavior based on how prey are located, either by sight (visual) or touch (tactile). Two examples that characterize visual and tactile feeding are Great Egrets and Wood Storks, respectively. Great Egrets hold their heads above the water searching for prey and then strike at an individual prey item. Wood Storks, however, submerge their bills in the water and hold them open until they come into contact with prey. At that moment, the bill snaps shut and the prey is captured.
Although some species are solitary feeders, many wading birds may form large feeding aggregations. These aggregations can include multiple species and typically form where prey are abundant and easily available, such as in shrinking wetlands where prey become concentrated. The highly visible plumage of white wading birds may even be an aid in the establishment of feeding aggregations because it makes individuals more conspicuous to other birds flying in the area (Kushlan 1977).
Wading birds as a group eat a variety of foods and will usually feed in waters no deeper than their legs are long. All wading birds are carnivores, but prey items vary from invertebrates to vertebrates, worms to mammals, and aquatic species to terrestrial species. Generally speaking, fish are the main food source for Florida's wading birds, but invertebrates such as crayfish can be very important as well. Prey sizes differ based on the size of the predator in many animals, and wading birds are no different. Larger birds tend to take larger prey, and longer legs mean greater accessibility to prey in deeper water. Wading birds that attempt to swallow anything that is too large, however, run the risk of choking.
Breeding among south Florida's wading birds peaks around April and May, although different species certainly vary and breeding periods are all longer than two months out of the year. In fact, wading birds nest asynchronously, which means that they do not all breed at the same time. Even within a nest, eggs are laid in intervals. The result of asynchronous nesting is that a group of birds will maintain a wide variety of stages of nesting at any given point in time. A comparison of the breeding periods of Florida's wading birds is summarized in Table 3. Wading birds attempt to nest during periods of high food availability in order to increase their likelihood of successfully raising young. In the Everglades, the timing for nesting and raising young is correlated to the natural drawdown of water, a time when food becomes naturally concentrated and more accessible. Breeding efforts generally cease when the rainy season begins. At this time of year in the Everglades, aquatic prey become scattered and exposure to the elements is harder to endure.
Wading birds are colonial nesters and often nest over water. Researchers speculate that nesting over water provides some protection from mammalian predators, likely due to the water itself being a physical barrier and the potential threat of alligators (Frederick and Collopy 1989). Other predators of nests include Fish Crows (Corvus ossifragus), snakes, and night-herons.
The distribution of information is another advantage of wading bird nesting behavior. The direction of high-quality foraging sites is valuable knowledge since foraging sites may be scattered over a large area. Wading birds within a colony have better opportunities to observe the relative success of returning individuals (e.g., feeding chicks) and observe from which direction successful birds arrive. By living in close proximity to one another within a colony, wading birds have the opportunity to obtain information from their neighbors about the surrounding landscape and make decisions about where to feed accordingly.
As with many of North America's birds, many wading birds migrate south for the winter. Migration is the seasonal movement of an animal, usually over long distances, to more suitable habitat. Florida's subtropical climate and historically expansive wetlands complex make it an ideal winter retreat for birds from more temperate climates. Some of these birds move into Florida only to spend the winter, and others migrate to Florida to nest (Robertson and Kushlan 1974). Not all wading birds present in Florida in the winter are migratory. Many are permanent residents that can be seen throughout the year.
Wading birds travel for other reasons than migration. Kushlan (1981) identified dispersal and intraregional movement as two other types of population movements. Dispersal occurs at the end of the breeding season, when nesting colonies disband and individuals seek out more available resources. Intraregional movements are more localized than both dispersal and migration and are linked to prey availability. Wading birds are capable of making long flights on a daily basis. For example, Wood Storks have been observed to undertake feeding flights as long as 80 miles (Ogden et al. 1978), but typical flights to feeding grounds are between 1 and 6 miles (Custer and Osborn 1978).
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