The Cranes
Status Survey and Conservation Action Plan
Evolution and Classification
Within the order Gruiformes, cranes are closely related to the limpkins (which have similar flight patterns and loud calls), the trumpeters (which resemble Crowned Cranes in their dances and plumage), and the bustards (which are also large, long-legged, long-necked birds found in open lands). Recent studies of morphology, ethology, and DNA have shown similar patterns in the systematic relationships within this order of birds (see Archibald 1976a, 1976b; Wood 1979; Krajewski 1989; Krajewski and Fetzner 1994; Krajewski and Archibald in prep.).
The crane family (Gruidae) is divided into two subfamilies, the Crowned Cranes (Balearicinae) and the Typical Cranes (Gruinae) (Figure 1.1). Crowned Cranes date back in the fossil record to the Eocene, 37-54 million years before present. Eleven species of Crowned Cranes are known to have existed in Europe and North America over the last 50 million years. The two species of Crowned Cranes that survive are found exclusively in Africa (Urban 1987). Modern Crowned Cranes cannot withstand extreme cold, and it is conjectured that as the earth cooled these cranes died out on the northern continents and held on only in Africa, where tropical conditions persisted through the Pleistocene. The Typical Cranes, by contrast, are more cold hardy. They first appear in the fossil record in the Miocene, 5-24 million years ago. It was during this period that the thirteen surviving species of Gruinae evolved. Seven other species of Gruinae cranes are known to have gone extinct during this period (Brodkorb 1967).
Crowned Cranes are distinguished from the Typical Cranes by their lack of a coiled trachea, their loose body plumage, and their inability to withstand severe cold. They retain the ability to roost in trees, and are the only cranes able to do so. Their calls are also simpler than those of the Typical Cranes (Archibald 1976a, 1976b). There are two species: the Black Crowned Crane (Balearica pavonina) of the African Sahel Savannah from Senegal to Ethiopia, and the Grey Crowned Crane (B. regulorum) of the East African savannahs from Kenya to South Africa.
The Typical Cranes are divided into three genera: Anthropoides, Bugeranus, and Grus. The Demoiselle Crane (Anthropoides virgo) and Blue Crane (Anthropoides paradisea) have bustard-like short toes and bills, and like the bustards live in grasslands. Although the morphological features of the Anthropoides species and the larger Wattled Crane (Bugeranus carunculatus) are dramatically different, studies of their behavior and DNA indicate a close relationship between them (Archibald 1976a, 1976b; Krajewski 1989; Krajewski and Fetzner 1994). The Wattled Crane is a much more aquatic species, and undoubtedly its large size is an evolutionarily convergent feature that it shares with the Grus species that are primarily aquatic.
The species in the genus Grus are placed in four groups (Archibald 1976a, 1976b; Krajewski 1989; Krajewski and Archibald in prep.). The Sandhill Crane (Grus canadensis) stands alone, as does the Siberian Crane (Grus leucogeranus). The “Group of Three” includes the Sarus Crane (Grus antigone), the Brolga (Grus rubicundus), and the White-naped Crane (Grus vipio). The “Group of Five” consists of the Eurasian Crane (Grus grus), Whooping Crane (Grus americana), Hooded Crane (Grus monachus), Black-necked Crane (Grus nigricollis), and Red-crowned Crane (Grus japonensis).
The differences between the Siberian Crane and the other Grus species are greater than those that separate the remaining eight species. There are some morphological and ethological similarities between the Siberian and Wattled Crane, although DNA evidence suggests that these are due to convergent evolution. Many scientists hold that the Siberian Crane should be placed within its own distinct genus, Sarcogeranus. The Sandhill Crane has features in common with both the Group of Three and the Group of Five, which suggests that it might be (or might resemble) the common ancestor of the two groups. Although the Sarus Crane and Brolga are similar morphologically, DNA analysis suggests that the Brolga and White-naped Crane are actually more closely related. The Common Crane is closest to the Whooping Crane, and the Hooded Crane closest to the Black-necked Crane. Within the Group of Five, the Red-crowned Crane is the most distantly related to the other four species (Krajewski and Fetzner 1994).
Each of the two Crowned Crane species has two subspecies. The Grey Crowned Crane is divided into the South African Crowned Crane (B. r. regulorum) and the East African Crowned Crane (B. r. gibbericeps). The Black Crowned Crane is divided into the West African Crowned Crane (B. p. pavonina) and the Sudan Crowned Crane (B. p. ceciliae). The Sarus Crane has three subspecies: the Indian (G. a. antigone), Eastern (G. a. sharpii), and Australian (G. a. gilli). The Philippine Sarus Crane (G. a. luzonica), which is presumed to be extinct, may have been a discrete subspecies. Six subspecies of Sandhill Cranes are currently recognized: the Lesser (G. c. canadensis), Canadian (G. c. rowani), Greater (G. c. tabida), Mississippi (G. c. pulla), Florida (G. c. pratensis), and Cuban (G. c. nesiotes) Sandhill Cranes. In the past, the Eurasian Crane was split into two subspecies—the western (G. g. grus) and eastern (G. g. lilfordi)—and the Brolga into Northern (G. r. argentea) and Southern (G. r. rubicundus) subspecies, but these divisions have not been validated and are not widely accepted. (See the species accounts in Section 2 for further discussion of the taxonomic status and characteristics of subspecies).
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