Coraciiformes (Kingfishers, Todies, Hoopoes, and Relatives)
(Kingfishers, todies, hoopoes, and relatives)
Number of families 8
Number of genera, species 49 genera; 211 species
The order Coraciiformes includes many species that represent some of the most colorful and unusual bird families in the world. The order is named after the rollers of the family Coraciidae, whose members have the least specialized or most basic design within the order. While each family within the Coraciiformes can be defined rather clearly, relationships between the families (and which families to include in the order) are more difficult to ascertain. This also means that the exact criteria for membership in the order are difficult to define, due to the diversity of form and behavior spread across such variable families. Ten families are usually incorporated into the Coraciiformes and these can be divided into four main groups. This approach will be adopted here; each group is sometimes designated as a sub-order:
- Kingfishers (family Alcedinidae) and the allied families of todies (family Todidae) and motmots (family Momotidae) in the suborder Alcedines.
- Bee-eaters (family Meropidae) alone in the suborder Meropes.
- Rollers (family Coraciidae) alone in the suborder Coracii. The allied families of ground-rollers (family Brachypteraciidae) and the anomalous cuckoo-roller or courol (family Leptosomidae) are commonly included as Coracii in other treatments.
- Hornbills (family Bucerotidae) and the closely related common hoopoe (family Upupidae) and woodhoopoes (family Phoeniculidae) in the sub-order Bucerotes.
Given the diversity of the order, other arrangements of the Coraciiformes have been proposed. On the one hand, some other families have been proposed for membership to a wider and more inclusive order Coraciiformes, such as the trogons (family Trogonidae), jacamars (family Galbulidae), and puff-birds (family Bucconidae). Of these, the trogons, with their worldwide and tropical distribution, are prime contenders for inclusion; although they differ in the unique heterodactyl arrangement of their toes, they are similar to other Coraciiformes in many other features. On the other hand, several coraciiform families have been elevated to the level of an order, such as the todies, hornbills, and hoopoes, while several subfamilies have been elevated to the level of families, such as the kingfishers, hoopoes, and hornbills. More distant relatives of Coraciiformes have been proposed to occur mainly among the woodpeckers and barbets, and especially the jacamars and puffbirds, of the Piciformes, but also among the trogons of the Trogoniformes, the cuckoos of the Cuculiformes, and the mousebirds of the Coliiformes. The rollers sensu lato have also been proposed as the primitive evolutionary template that gave rise to the sub-oscines, such as broadbills and pittas. All of these orders have been proposed to be precursors to the great avian order of the oscine Passeriformes, a suggestion based in part on the different and possibly relict forms that are now isolated on Madagascar.
Many studies have attempted to unravel the relationships among families that might be included in the Coraciiformes. These range from anatomical studies, popular in the eighteenth century, to modern molecular studies of nuclear and mitochondrial DNA, such as the pioneering work of Charles Sibley and Jon Ahlquist (1990) on proteins from the whites of the eggs published in 1972 and on the hybridization of nuclear DNA in 1990. There is now some consensus on how the natural family groups cluster together, based wherever possible on unique shared features, reflected partly in the subordinal
divisions above and supported by some of the characteristics listed above and below. The common hoopoe and woodhoopoes are related by the unique anvil-shaped bone of the inner ear bone, while their most similar relatives, also with oval eggs and pitted shells, appear to be hornbills, which are defined by their uniquely fused neck vertebrae, the atlas and axis. The two special New World families of todies and motmots, as might be expected from their distribution, appear to be each other's closest relatives. These families are linked by species of intermediate characteristics, such as the tody motmot (Hylomanes momotula), and the connection is supported by a useful fossil record that shows an earlier and wider diversity in the Northern Hemisphere. Their biology also supports a more distant link with either the kingfishers, reflected in the diminutive kingfisher-like form of some todies and inclusion in the suborder Alcidines, or the bee-eaters, alone in their sub-order Meropes but linked by the heavy bee-eater-like bill and the behavior of the larger motmots. It is notable that most members of these last four families excavate their own nests as tunnels into the ground, termite nests, or epiphyte roots, while only a minority of members use natural tree or ground holes. They all share the stirrup-shaped inner ear bone, together with trogons, and they all have chicks with well-developed pads on the "heels."
Coraciiformes are generally recognized by the large and long bill, large head, short neck, short legs, and weak feet with short toes. The single feature shared by almost all families in the Coraciiformes is that the front three toes are fused partially at the base. The middle toe is fused to the inner toe at its base and to the outer toe for most of its length. This toefusion is a condition termed syndactyly and is the main criterion by which the order is defined. Coraciiformes also share, but are not unique, in the design of the palate bones (classified as desmognathous), in the lack of an ambiens muscle in the leg, and in the rather small feet.
Other features are widespread in the order but not present in or unique to each family. The wing has 10 primary feathers, often with a vestigial eleventh feather; the tail has 12 feathers in all families other than the motmots, hoopoes, and hornbills, for whom the tail has 10 feathers. The breast bone has two notches on the sternum in most families, but only one notch in common hoopoes (Upupa epops) and hornbills. The inner ear bone, or columella (stapes), is of a simple reptilian design in rollers and hornbills, but of a unique anvil-like shape in hoopoes and woodhoopoes, and of a stirrup-like shape in kingfishers, bee-eaters, todies, motmots, and trogons. The eggs are generally white, rounded, and shiny, except for being oval in hoopoes and hornbills, and tinted light blue-green in hoopoes. The chicks hatch blind and with the upper mandible noticeably shorter than the lower. The chicks are naked in all families, except for hoopoes, which have patches of fine down. However, the chicks always develop later through a spiky "pin-cushion" stage, when their emerging feathers are retained in their quills for several days. Kingfishers and bee-eaters excavate and nest in earthen burrows, and their chicks have well-developed papillae on their "heel" joint, similar to those of honeyguides and woodpeckers (Piciformes). Sexes are similar in most species, except for most hornbills and some kingfishers. Many species have a brilliant plumage, often with a large colorful bill, long tail, or tall crest. While there is no single character that is unique to and defines any combination of families that might comprise the Coraciiformes, there is an overlap in shared characters that links at least the ten main families as presented here.
Most coraciiform species are arboreal in their feeding, breeding, and roosting habits, though a minority of species spend much time on the ground. Most species feed on small animals, especially small vertebrates and large arthropods, and they catch their prey mainly by dropping down from a perch to the ground (e.g., true rollers) or into water (e.g., kingfishers). More aerial species may hover in search of prey (e.g., kingfishers), or they may take most food by hawking it on the wing (e.g., bee-eaters and broad-billed rollers). Many species, such the todies and motmots, combine terrestrial and aerial capture of prey into their foraging repertoire, often in quite different proportions. A few species are specialized in their foraging habits or diet; for example, bee-eaters de-venom their prey, cuckoo-rollers concentrate on chameleons, and shovel-billed kingfishers (Clytoccyx rex) specialize on earthworms. A few species collect most of their food while they walk or run about on the ground, such as the common hoopoes and some African hornbills. Other species consume fruit as their main diet and only add animal food secondarily when rearing chicks, as seen for many forest hornbills.
Most species are territorial when breeding, usually as single pairs, but in several families there are species that live and breed as cooperative groups or even some species that nest in large colonies. Most species lay their eggs inside a cavity (often sparsely lined with plant materials), which can
be either a natural hole in a tree, a rock face, a building, or the ground, or an excavated tunnel in the ground with a nest chamber at the end. Interestingly, some kingfisher species excavate nest cavities in arboreal termite nests, rotten wood, or even sawdust piles. Most hornbills exhibit the unique habit of sealing the entrance of the nest to form a narrow slit. In all species, both members of a pair generally take part in nesting activities, including defense, construction, and delivery of food. In most species, the female does most or all of the incubation of eggs and the brooding of young chicks, while the male delivers food to the female and the chicks. Only later, when the demands of the growing chicks rise, are both sexes involved in provisioning at the nest. The nest-tunnels of bee-eaters, motmots, todies, rollers, and especially kingfishers become quite smelly as nesting progresses due to the accumulation of feces and the remains of food in the chamber. The chicks of hoopoes also produce a noxious odor in the nest, apparently a mixture of preen oil, copious feces, and possibly with the aid of special bacterial products. Only the hornbills practice good nest sanitation, which is accomplished by squirting out feces and tossing out food remains through the partly sealed nest entrance.
Distribution and evolution
Even though the order Coraciiformes is cosmopolitan, it is only the kingfishers that occur widely across every ice-free continent. Many other families have very restricted ranges. The only other families that occur in the New World are the few species of motmots, confined to the tropics of Central and South America, and of todies, confined to the few islands of the Greater Antilles in the West Indies. Most families and species occur in the Old World. Even though bee-eaters, rollers, hoopoes, and hornbills range widely across Africa, Eurasia, and even into Australasia, all of the woodhoopoes and the majority of bee-eaters and rollers occur in Africa. Horn-bills are divided mainly between Africa and Asia with only a single species extending to Australasia. The kingfishers, despite their comopolitan distribution, have only six of their 91 species in the Americas. To the north of this mainly tropical distribution, only one species of kingfisher, bee-eater, and roller and the hoopoe breed in Europe. To the south, only one species of bee-eater and roller breeds in Australia; however, these species are joined there by at least ten species of kingfishers in what is the major and Australasian center for the diversity of that family.
The distribution of the fossilized remains of coraciiform birds suggests an ancient and somewhat different geographic and evolutionary history than what might be inferred from the current range of each family. Fossil evidence suggests that coraciiform birds were the dominant radiation of arboreal perching birds in North America and Europe by the early Tertiary, about 60 million years before present. This evidence includes the remains of a roller-like bird, Halcyornis, from England and a motmot-like bird, Protornis, from Switzerland. Despite a currently wide distribution,
no examples of kingfishers are yet recorded from this original radiation. More recently, from 25 to 40 million years ago, the remains of kingfisher-like birds are known from Wyoming, Germany, and France; of roller-like birds from France, Germany, and Wyoming; of hoopoe-like birds from France; and of tody-like birds from Wyoming and France. Even more recently, fossil kingfishers are also known from Australia. The Northern Hemisphere origin of motmots, and probably of todies, is supported even further by a 20-million-year-old motmot-like fossil from Florida. This species must have existed well before North and South America were finally connected (as recently as 2.5 million years ago), and is consistent with motmots and todies being the only avian families with their main diversity in Central America.
The Coraciiformes provide an ideal example to caution us against making assumptions about the history of the range and diversity of any group of birds based only on the present distribution and design of its members.
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Coraciiformes Taxon Advisory Group. Web site: <http://www.coraciiformestag.com>
Alan C. Kemp, PhD