Traditionally, the order Ciconiiformes has included a variety of large, long-legged wading birds with large bills: storks, herons, egrets, ibises, spoonbills, and several others. Ciconiiformes are known from the Late Eocene.
Following the development of microbiological research techniques in the late 20th century, in particular methods for studying DNA-DNA hybridisation, a great deal of new information has surfaced, much of it suggesting that many birds, although looking very different to one another, are in fact more closely related than was previously thought. Accordingly, the radical and influential Sibley-Ahlquist taxonomy greatly enlarged the Ciconiiformes, adding many more families, including most of those usually regarded as belonging to the Sphenisciformes (penguins), Gaviiformes (divers). Podicipediformes (grebes), Procellariiformes (tubenosed seabirds), Charadriiformes, (waders, gulls, terns and auks), Pelecaniformes (pelicans, cormorants, gannets and allies), and the Falconiformes (diurnal birds of prey).
However, morphological evidence suggests that the traditional Ciconiiformes should be split between two lineages, rather than expanded, although some non-traditional Ciconiiformes may be included in these two lineages.
Some official bodies, notably the American Ornithologists' Union, have adopted the proposed Sibley-Ahlquist taxonomy almost entirely, however a more common approach worldwide has been to retain the traditional groupings, and modify rather than replace them in the light of new evidence as it comes to hand. The family listing here follows this more conservative practice. Bird taxonomy has been in a state of flux for some years, and it is reasonable to expect that the large differences between different classification schemes will continue to gradually resolve theselves as more evidence becomes available.
In most cultures, at least some members of the Ciconiiformes — herons, storks, ibis, egrets and so on — have always had an unusual status as objects of religious or artistic veneration. The attraction is certainly not phylogenetic. The morphologically similar, but unrelated, cranes are treated in the same way.
Sometimes hauntingly beautiful evocations of these birds are known from antiquity in, for example, Greece, Africa, Egypt, China and Japan. In Indo-European cultures the long-legged water bird tends to be a comical or even evil figure. The cultural phylogeny of these symbols would be an interesting study in itself, and their relative stability over millennia is surprising.
Certainly one of the reasons for the attention given the ciconiiformes is their strange and alien way of moving. That special style of movement, whether perceived as graceful or comically awkward, is emphasized in the behavioral rituals common in the group. Some ciconiiforms are completely silent, and vocalization in most species is fairly limited. Thus, rituals and displays are the primary means of communication.
These behaviors seem to be genetically determined almost completely. In fact, one study analyzed the ritual behaviors of storks as if they were anatomical characters and reconstructed a taxonomic tree almost identical to the trees arrived at by anatomical or biochemical characteristics.
The rituals associated with initial mate selection, such as the male's "advertising" of his nest site and the female's expression of interest in the male's real estate, were quite extraordinarily stable.
Behaviours related to later events, such as copulation and pair-bond affirmation seem to be more phylogenetically plastic. Finally, behaviors not related to mating, such as the "anxiety stretch" or aggression displays, were quite variable, but still clearly inherited. This contrasts strongly with the song behaviors of passerine birds, which are strongly influenced by learning and individual experience.
Ciconiiformes have only a single pair of sternotracheal muscles in the syrinx; 16–20 cervical vertebrae; are diastataxic (the fifth secondary feather is absent, but fifth secondary covert is present); the feet are not webbed; the middle claw is laterally expanded, (pectinate in some families); intestinal ceca present, nearly always very small.
Ciconiiformes are primarily occupy fresh water or terrestrial habitat, they are not filter feeders, and mostly feed on fish, crustaceans, insects, and carrion. They do not swim for food, and the northerly species migrate. They are strong flyers with broad wings.
Most nest in trees although some build nests in swamps or on the ground. The young are altricial. Most species are generally colonial but the use of sound is uncommon. Social communication is by displays and rituals.
- Order Ciconiiformes
- Family Ardeidae, (herons, egrets, and bitterns)
- Family Cochlearidae, (Boatbill)
- Family Balaenicipitidae, (Shoebill)
- Family Scopidae, (Hammerkop)
- Family Ciconiidae, (storks)
- Family Threskiornithidae, (ibises and spoonbills)
- The flamingo family, Phoenicopteridae, is related, and is sometimes classed as part of the Ciconiiformes.
- Slikas, B (1998), "Recognizing and testing homology of courtship displays in storks (Aves: Ciconiiformes: Ciconiidae)". Evolution 52: 884–893.