Stork
Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae, and make up the order Ciconiiformes. Ciconiiformes previously included a number of other families, such as herons and ibises, but those families have been moved to the order Pelecaniformes.
Storks dwell in many regions and tend to live in drier habitats than the closely related herons, spoonbills and ibises; they also lack the powder down that those groups use to clean off fish slime. Bill-clattering is an important mode of communication at the nest. Many species are migratory. Most storks eat frogs, fish, insects, earthworms, small birds and small mammals. There are 20 living species of storks in six genera.
Various terms are used to refer to groups of storks, two frequently used ones being a muster of storks and a phalanx of storks.
Storks tend to use soaring, gliding flight, which conserves energy. Soaring requires thermal air currents. Ottomar Anschütz's famous 1884 album of photographs of storks inspired the design of Otto Lilienthal's experimental gliders of the late nineteenth century. Storks are heavy, with wide wingspans: the marabou stork, with a wingspan of and weight up to, joins the Andean condor in having the widest wingspan of all living land birds.
Their nests are often very large and may be used for many years. Some nests have been known to grow to over in diameter and about in depth. All storks were once thought to be monogamous, but this is only partially true. While storks are generally socially monogamous, some species exhibit regular extra-pair breeding.
Popular conceptions of storks' fidelity, serial monogamy, and doting parental care contribute to their prominence in mythology and culture, especially in Western folklore as the deliverers of newborn humans.
All 20 stork species have been assessed by the IUCN and carry a confident Red List status. However, the assessments for several species were based on incorrect assumptions and a general lack of sound information on stork habits.
Etymology
The word "stork" was first used in its current sense by at least the 12th century in Middle English. It is derived from the Old English word storc, which itself comes from the hypothesised Proto-Germanic *stork and ultimately the Proto-Indo-European *sr̥ǵos. The name refers to the rigid posture of storks, a meaning reflected in the related word stark, which is derived from the Old English stearc. Several species of storks are known by other common names. The jabiru is named after the Tupí-Guarani words meaning "that which has" and "swollen", referring to its thickset neck. The marabou stork is named after the Arabic word for holy man,, due to the perceived holy nature of the species. The adjutants are named after the military rank, referring to their stiff, military-like gait.Systematics
A DNA study found that the families Ardeidae, Balaenicipitidae, Scopidae and the Threskiornithidae belong to the Pelecaniformes. This would make Ciconiidae the only group.Storks were distinct and possibly widespread by the Oligocene. Like most families of aquatic birds, storks seem to have arisen in the Palaeogene, maybe 40–50 million years ago. For the fossil record of living genera, documented since the Middle Miocene at least in some cases, see the genus articles.
No species or subspecies of stork is known to have gone extinct in historic times. A systematic literature review uncovered nearly 1,000 papers on storks, but showed most stork species to lack scientific understanding, suggesting that many species should be classified as Data Deficient on the IUCN Red List. A Ciconia bone found in a rock shelter on the island of Réunion was probably of a bird taken there as food by early settlers; no known account mentions the presence of storks on the Mascarene Islands.
Phylogeny
The following phylogeny is recognized by the International Ornithological Congress, partially based on de Sousa et al :Fossil storks
- Genus Palaeoephippiorhynchus
- Genus Grallavis – may be same as Prociconia
- Ciconiidae gen. et sp. indet. – formerly Aquilavus/Cygnus bilinicus
- Ciconiidae gen. et sp. indet.
- Ciconiidae gen. et sp. indet.
- cf. Leptoptilos gen. et sp. indet. – formerly L. siwalicensis
- Ciconia nana
- Genus Prociconia – may belong to modern genus Jabiru or Ciconia
- Ciconiidae gen. et sp. indet.
Morphology
Storks range in size from the marabou, which stands tall and can weigh, to the Abdim's stork, which is only high and weighs only. Their shape is superficially similar to the herons, with long legs and necks, but they are more heavy-set. There is some sexual dimorphism in size, with males being up to 15% bigger than females in some species, but almost no difference in appearance. The only difference is in the colour of the iris of the two species in the genus Ephippiorhynchus.The bills of storks are large to very large, and vary considerably between the genera. The shape of the bills is linked to the diet of the different species. The large bills of the Ciconia storks are the least specialized. Larger are the massive and slightly upturned bills of the Ephippiorhynchus and the jabiru. These have evolved to hunt for fish in shallow water. Larger still are the massive daggers of the two adjutants and marabou, which are used to feed on carrion and in defense against other scavengers, as well as for taking other prey. The long, ibis-like downcurved bills of the Mycteria storks have sensitive tips that allow them to detect prey by touch where cloudy conditions would not allow them to see it. The most specialised bills of any storks are those of the two openbills, which as their name suggests, is open in the middle when their bill is closed. These bills have evolved to help openbills feed on their primary prey item, aquatic snails.
Although it is sometimes reported that storks lack syrinxes and are mute, they do have syrinxes, and are capable of making some sounds, although they do not do so often. The syrinxes of storks are "variably degenerate" however, and the syringeal membranes of some species are found between tracheal rings or cartilage, an unusual arrangement shared with the ovenbirds.
Distribution and habitat
Storks have a nearly cosmopolitan distribution, being absent from the poles, most of North America and large parts of Australia. The centres of stork diversity are in tropical Asia and sub-Saharan Africa, with eight and six breeding species respectively. Just three species are present in the New World: wood stork, maguari stork and jabiru, which is the tallest flying bird of the Americas. Two species, white and black stork, reach Europe and western temperate Asia, while one species, Oriental stork, reaches temperate areas of eastern Asia, and one species, black-necked stork, is found in Australasia.Storks are more diverse and common in the tropics, and the species that live in temperate climates for the most part migrate to avoid the worst of winter. They are fairly diverse in their habitat requirements. Some species, particularly the Mycteria "wood storks" and Anastomus openbills, are highly dependent on water and aquatic prey, but many other species are far less dependent on this habitat type, although they will frequently make use of it. Species like the marabou and Abdim's stork will frequently be found foraging in open grasslands of savannah. Preferred habitats include flooded grasslands, light woodland, marshes and paddyfields, wet meadows, river backwaters and ponds. Many species will select shallow pools, particularly when lakes or rivers are drying out, as they concentrate prey and make it harder for prey to escape, or when monsoonal rainfall increases water depth of larger waterbodies. Some species like the woolly-necked storks and lesser adjutant storks have adapted to changing crops of tropical agricultural landscapes that enables them to remain resident despite the transformations brought about by seasonal crops. In South Africa, the woolly-necked storks have adapted to artificial feeding and now largely nest on trees in gardens with swimming pools.
Less typical habitats include the dense temperate forests used by European black storks, or the rainforest habitat sought by Storm's stork in South East Asia. They generally avoid marine habitats, with the exception of the lesser adjutant, milky stork and wood stork, all of which forage in mangroves, lagoons and estuarine mudflats. A number of species, especially woolly-necked storks, black-necked storks, Asian openbills, and lesser adjutant Storks in South Asia, have adapted to highly modified human habitats for foraging and breeding. In the absence of persecution several stork species breed close to people, and species such as the marabou, greater adjutant, and white stork feed at landfill sites.
Migration and movements
Storks vary in their tendency towards migration. Temperate species like the white stork, black stork and Oriental stork undertake long annual migrations in the winter. The routes taken by these species have developed to avoid long-distance travel across water, and from Europe, this usually means flying across the Straits of Gibraltar or east across the Bosphorus and through Israel and the Sinai. Studies of young birds denied the chance to travel with others of their species have shown that these routes are at least partially learnt, rather than being innate as they are in passerine migrants. Migrating black storks are split between those that make stopovers on the migration between Europe and their wintering grounds in Africa, and those that do not.The Abdim's stork is another migrant, albeit one that migrates within the tropics. It breeds in northern Africa, from Senegal to the Red Sea, during the wet season, and then migrates to Southern Africa. Many species that are not regular migrants will still make smaller movements if circumstances require it; others may migrate over part of their range. This can also include regular commutes from nesting sites to feeding areas. Wood storks have been observed feeding from their breeding colony.