Yellow-billed stork

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Yellow-billed stork
A breeding adult in South Africa
and a juvenile bird in Tanzania

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Ciconiiformes
Family: Ciconiidae
Genus: Mycteria
Species:
M. ibis
Binomial name
Mycteria ibis
(Linnaeus, 1766)
Synonyms

Tantalus ibis Linnaeus, 1766

The yellow-billed stork (Mycteria ibis), sometimes also called the wood stork or wood

Ciconiidae. It is widespread in regions south of the Sahara and also occurs in Madagascar
.

Taxonomy and evolution

The yellow-billed stork is closely related to three other species in the genus Mycteria: the

courtship behaviours of the wood-stork family, M.P. Kahl attributed the same general ethology to all members of the genus Mycteria, with relatively few species-specific variations.[3]
These four species are collectively referred to as the wood-storks, which should not be confused with one alternative common name (wood-stork) for the yellow-billed stork.

Before it was established that the yellow-billed stork was closely related to the American wood stork, the former was assigned to the genus Ibis, together with the milky stork and painted stork.[4] However, the yellow-billed stork has actually long been recognised as a true stork[5][6] and along with the other 3 related stork species, it should not strictly be called an ibis.[4]

Description

Vivid colours of breeding plumage, Zambia
Adult in flight, Zambia
Juvenile in flight, Zambia

This medium-sized stork stands 90–105 cm (35–41 in) tall.

moulted.[4] The bill is deep yellow, slightly decurved at the end and with a rounder cross-section than in other stork species outside the Mycteria.[4] Feathers extend onto the head and neck just behind the eyes, with the face and forehead being covered by deep red skin. Both sexes are similar in appearance, but the male is larger and has a slightly longer heavier bill.[3] Males and females weigh approximately 2.3 kg (5.1 lb) and 1.9 kg (4.2 lb) respectively.[7]

Colouration becomes more vivid during the breeding season. In the breeding season, the plumage is coloured pink on the upperwings and back;[3] the ordinarily brown legs also turn bright pink; the bill becomes a deeper yellow and the face becomes a deeper red.[4]

Flight feathers on the tail and wing also become black. Later, the pink colouration typical of adult plumage appears.[4]

These storks walk with a high-stepped stalking

altitudes, this stork has been observed to dive deeply at high speeds and flip over and over from side to side,[3] hence showing impressive aerobatics. It even appears to enjoy these aerial stunts.[4]

This species is generally non-vocal, but will utter hissing

braying call to beg parental adults for food.[4]

Distribution and habitat

Flock in a seasonal wetland, Zambia

The yellow-billed stork occurs primarily in Eastern Africa,

individuals being counted at once.[4]

The species does not generally

habitats all year round.[4]

Preferred habitats include

mudflats, usually 10–40 cm deep[4] but it usually avoids heavily forested regions in central Africa.[4] It also avoids flooded regions and deep expansive bodies of water because feeding conditions there are unsuitable for their typical grope and stir feeding techniques.[4]

This species breeds especially in

Gambia down to northern Nigeria.[10] Still other breeding sites include Zululand in South Africa[11] and northern Botswana,[12] but are rarer below northern Botswana and Zimbabwe where sites are well-watered.[4] Although there is no direct evidence of current breeding in Madagascar, young birds unable to fly have been observed near Lake Kinkony during October.[13]

Behaviour and ecology

Food and feeding

This stork's diet mainly comprises small, freshwater

birds.[4]

This species appears to rely principally on sense of touch to detect and capture

mandibles, raises its head and swallows the prey whole.[3] The speed of this reflex in the closely related American woodstork (Mycteria americana) has been recorded as 25 milliseconds[15] and although the corresponding reflex in the yellow-billed stork has not been quantitatively measured,[3] the yellow-billed stork's feeding mechanism appears to be at least qualitatively identical to that of the American wood stork.[3]

In addition to the snap-bill reflex, the yellow-billed stork also uses a systematic foot stirring technique to sound out evasive prey.

cormorants.[8]

The yellow-billed stork has been observed to follow moving

hippopotami through the water and feed behind them, appearing to take advantage of organisms churned up by their quarry.[16] Feeding lasts for only a short time before the bird obtains its requirements and proceeds to rest again.[4]

Parents feed their young by regurgitating fish onto the nest floor, whereupon it is picked up and consumed by the

nestlings. The young eat voraciously and an individual nestling increases its body weight from 50 grams to 600 grams during the first ten days of its life.[4] Hence, this species has earned the German colloquial common name “Nimmersatt”;[4]
meaning “never full”.

Breeding behaviour

Breeding is seasonal and appears to be stimulated by the peak of long heavy rainfall

marshes, usually near Lake Victoria.[17] This flooding is linked to an increase in prey fish availability;[17][4] and reproduction is therefore synchronised with this peak in food availability. In such observations near Kisumu, M.P. Kahl's explanation for this trend was that in the dry season, most prey fish are forced to leave the dried-up, deoxygenated marshes that cannot support them and retreat to the deep waters of Lake Victoria where the storks cannot reach them.[17] However, fish move back up the streams on the onset of rain and spread out over the marshes to breed, where they become accessible to the storks. By nesting at this time and providing that the rains do not end pre-maturely, the storks are guaranteed a plentiful food supply for their young.[17]

The yellow-billed stork may also begin nesting and breeding at the end of long rains. This occurs especially on flat extensive marshlands as water levels gradually decrease and concentrate fish sufficiently for the storks to feed on.[4] However, unseasonal rainfall has also been reported to induce off-season breeding in northern Botswana[19] and western and eastern Kenya. Rainfall may cause local flooding and hence ideal feeding conditions.[4] This stork appears to breed simply when rainfall and local flooding are optimal and hence seems to be flexible in its temporal breeding pattern, which varies with rainfall pattern throughout the African continent.[4]

As with all stork species, male yellow-billed storks select and occupy potential nest sites in trees, whereupon females attempt to approach the males.

copulation. Generally, these courtship behaviours are also assumed to be common to all Mycteria species and show remarkable homology within the genus Mycteria.[3] After the male has initially established at the nesting-site and the female begins to approach, he displays behaviours that advertise himself to her. One of these is the Display Preening, whereby the male pretends to strip down each of his extended wings with the bill several times each side[3] and the bill does not effectively close around the feathers. Another observed display among males is the Swaying-Twig Grasping. Here, the male stands on the potential nesting-site and bends over to gently grasp and release underlying twigs at regular intervals.[3] This is sometimes accompanied by side-to-side oscillations of the neck and head and he continues to pick at twigs in between such movements.[3]

Reciprocally, approaching females display their own distinct behaviours. One such behaviour is the Balancing Posture,[3] whereby she walks with a horizontal body axis and extended wings toward the male occupying the nesting-site. Later, when the female continues to approach or already stands near an established male, she may also engage in Gaping. Here, the bill is gaped open slightly with the neck inclined upward at about 45°[3] and often occurs in conjunction with the Balancing Posture. This behaviour ordinarily continues if the male accepts the female and has allowed her to enter the nest, but the female usually closes her wings by this time.[3] The male may also continue his Display Preening when standing next to the female in the nest[3]

During copulation, the male steps onto the female's back from the side, hooks his feet over her shoulders, holds out his wings for balance and finally bends his legs to lower himself for

cloacal contact, as happens in most birds. In turn, the female holds out her wings almost horizontally. The process is accompanied by bill clattering from the male as he regularly opens and closes his mandibles and vigorously shakes his head to beat his bill against the female's.[3] In turn, the female keeps her bill horizontal with the male's, or inclined downward at approximately 45 degrees.[3] Average copulation time in this species has been calculated as 15.7 seconds.[3]

MHNT

The female typically lays 2-4

clutch size has been recorded as 2.5.[21] The male and female share duties to incubate the eggs, which takes up to 30 days.[4] As in many other stork species,[22][23] hatching is asynchronous (usually at 1- to 2-day intervals),[4] so that the young in the brood differ considerably in body size at any one time.[3] During food shortage, the smaller young are at risk of being outcompeted for food by their larger nest-mates.[3]

Both parents share duties of guarding and feeding the young until the latter are about 21 days old.[4] Thereafter, both parents forage to attend to the young's intense food demands.[4] Alongside parental feeding by regurgitation of fish, parents have also been observed to regurgitate water into the open bills of their nestlings,[24] especially on hot days. This may aid the typical thermoregulatory strategy of the young (common to all stork species)[3] to excrete dilute urine down their legs in response to hot weather.[3] Water regurgitated over the young serves as a water supplement in addition to fluid in their food, so that they have sufficient water to continue urinating down their legs to avoid hyperventilation.[3] Additionally, parents sometimes help keep the young cool by shading them with their open wings.[4]

The nestlings usually fledge after 50–55 days of hatching[3] and fly away from the nest. However, after leaving the nest for the first time, the offspring often return there to be fed by their parents and roost with them for another 1–3 weeks.[3] It is also thought that individuals are not fully adult until 3 years old[4] and despite lack of data, new adults are thought to not breed until much later than this.[4]

Fledglings have also been observed to not differ considerably in their foraging and feeding strategies from adults. In one investigation, four adult, hand-reared yellow-billed storks kept in captivity showed typical grope-feeding and foot stirring shortly after they were introduced to bodies of water.[3]
Hence, this suggests that such feeding techniques in this species are innate.

Nesting

Colony of nests in tall trees, Zambia
Stick nests on a tall tree, Zambia

The yellow-billed ibis is a colonial nester, often alongside other species;[21] but the yellow-billed stork is sometimes the only occupant species of a nesting site.[4] Colonies are usually 10-20 nests in size, with several males occupying potential nest sites all in the same place.[4] If many of these males do not acquire mates, the whole group moves on with the unpaired females to another tree. These “bachelor parties”[3] are a noticeable feature of colonies of this species and usually consist of 12 or more males and at least as many females.[3] As many as 50 nests have been counted all at once in a single breeding area.[10]

The male and female together build the nest of sticks either in high trees on dry land away from predators, or in small trees over water.[25][4] Nest building takes up to 10 days.[4] The nest may be 80–100 cm (31–39 in) in diameter and 20–30 cm (7.9–11.8 in) thick.[4]

Other behaviours

Despite their

gregariousness during breeding, most individuals generally ignore each other outside nesting-sites;[3] although some hostile encounters may occur. Some of these encounters involve one individual showing an unambiguous attack or escape response if there is a large difference in social status between the two individuals.[3] However, if two individuals are equally matched, they slowly approach each other and show a ritualised display called the Forward Threat.[3] Here, one individual holds its body forward horizontally and retracts the neck so that it touches the crown, with the tail cocked at 45 degrees and all feathers erect.[3] It approaches the opponent and points its bill at it, sometimes gaping.[3] If the opponent does not capitulate, the attacker may grab at it with its bill and the two may briefly spar with their bills until one retreats in an erect stance with compressed plumage.[3]

Hostility can also arise between opposite sexes when a female approaches a male on a potential nest site. Both sexes may display a similar aforementioned Forward Threat, but clatter their bills after grabbing with them at the other stork and extend their wings to maintain balance.[3] Another hostile behaviour between sexes is the Snap Display,[3] whereby they snap horizontally with their bills while standing upright. This may occur during and immediately after pair formation, but subsides later in the breeding cycle as the male and female become familiar with each other and it eventually disappears.[3]

Nestlings show remarkable behavioural transformations at 3 weeks of age. During the constant parental attendance before this time, the young show little fear or aggression in response to intruders (such as a human observer), but are found to merely crouch low and quietly in the nest.[3] After this time, when both parents go foraging and leave the young in the nest, a nestling shows strong fear in response to an intruder. It either attempts to climb out of the nest to escape or acts aggressively toward the intruder.[3]

Threats and survival

As well as being abundant and widespread, the yellow-billed stork also appears tolerant of short-term natural habitat changes.

AEWA).[26] Nevertheless, the overall population is not currently considered to be threatened with serious decline,[4] especially since breeding success is relatively high.[4] In East Africa where it is most abundant, broods of 1-3 per nest have been recorded.[21]

Alongside human activities, natural enemies include

African fish eagles.[28] At one colony in Kisumu, Kenya, approximately 61% of eggs counted between all nests hatched and 38% were predated by fish eagles.[28] The success rate of fledglings was only 0.33 young per nest.[28] However, increased egg predation by fish eagles has been reported to be linked to decline in fish stocks in the Winam Gulf.[28]

In culture or relationships to humans

The yellow-billed stork has appeared on postage stamps in several African countries.[29]

Status

This species is evaluated as

Least Concern for several reasons. First, population trend appears to be decreasing[30] but this decrease is not believed to rapidly approach thresholds for Vulnerable under the population trend criterion.[30] Its range is also very large and does not approach threshold for Vulnerable under range size criterion.[30] Finally, although there have been no official population size estimates,[8] the population is known to be very large and so does not approach thresholds for Vulnerable under population size criterion.[30]

Gallery

  • Immature at Maasai Mara National Reserve
    Immature at
    Maasai Mara National Reserve
  • Storks sometimes rest on their hocks (analogous to a human's heels)
    Storks sometimes rest on their hocks (analogous to a human's heels)
  • Juveniles have grey backs, mature birds have white backs
    Juveniles have grey backs, mature birds have white backs
  • Fishing in shallow water
    Fishing in shallow water
  • Juvenile
    Juvenile
  • Flock at Lake Nakuru National Park, Kenya
    Flock at Lake Nakuru National Park, Kenya
  • Weltvogelpark Walsrode, Germany
    Weltvogelpark Walsrode, Germany
  • With a Nile crocodile at Kazinga Channel, Uganda
    With a Nile crocodile at Kazinga Channel, Uganda
  • Chobe National Park, Botswana
    Chobe National Park, Botswana
  • On the bank of a river
    On the bank of a river

References

Wikimedia Commons has media related to Mycteria ibis.
Wikispecies has information related to Mycteria ibis.
  1. doi:10.2305/IUCN.UK.2016-3.RLTS.T22697654A93628112.en
    . Retrieved 19 November 2021.
  2. ^ Peters
  3. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay Kahl, Ibis
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay Hancock, et al.
  5. ^ Garrod, On the form...
  6. ^ Garrod, On the disposition...
  7. ^ Sinclair, et al.
  8. ^ a b c d e Kasoma and Pomeroy
  9. ^ Rand
  10. ^ a b Bannerman
  11. ^ Clancey
  12. ^ Fraser
  13. ^ Langrand
  14. ^ Bell-Cross
  15. ^ Kahl and Peacock
  16. ^ Pooley
  17. ^ a b c d e Kahl, Journal of East African Natural History Society and National Museum
  18. ^ Brown and Britton
  19. ^ Tree
  20. ^ "Yellow-Billed Stork".
  21. ^ a b c Brown, et al.
  22. ^ Schüz
  23. ^ Kahl, Ecological Monographs
  24. ^ Stronach
  25. ^ Andrew, Elliott; Garcia, Ernest; Boesman, Peter F. D. (March 4, 2020). "Yellow-billed Stork Mycteria ibis". Birds of the World (1.0 ed.). Retrieved 16 August 2023.
  26. ^ "Yellow-billed stork videos, photos and facts - Mycteria ibis | ARKive". Archived from the original on 2015-04-02. Retrieved 2015-03-15.
  27. ^ "Yellow-billed Stork - DesertUSA".
  28. ^ a b c d Parsons
  29. ^ "Yellow-billed Stork stamps". Archived from the original on October 19, 2000.{{cite web}}: CS1 maint: unfit URL (link)
  30. ^ a b c d "Yellow-billed Stork (Mycteria ibis) - BirdLife species factsheet". www.birdlife.org. Archived from the original on 2012-09-24.

Sources

  • Bannerman, D.A. (1953). The birds of west and equatorial Africa, Vol. 1.
    Oliver & Boyd
    : London.
  • Bell-Cross, G. (1974). "Observations on fish-eating birds in central Africa". Honeyguide, 77: 23–31.
  • Brown, L.H., and Britton, P.L. (1980). The Breeding Seasons of East African Birds. East African Natural History Society: London.
  • Brown, L.H., Urban, E.K., and Newman, K. (1982). The Birds of Africa, Vol. 1. Academic Press: London.
  • Clancey, P.A. (1964). The Birds of Natal and Zuzuland.
    Oliver & Boyd
    : London.
  • Fraser, W. (1971). "Breeding herons and storks in Botswana". Ostrich, 42: 123–127.
  • Garrod, A.H. (1875a). On the form of trachea in certain species of storks and spoonbills. Proceedings of the Zoological Society of London, 1875: 297–301.
  • Garrod, A.H. (1875b). On the disposition of the deep planar tendons in different birds. Proceedings of the Zoological Society of London, 1875: 339–348.
  • James, Peter L. (1931). Checklist of the Birds of the World, Vol 1. Harvard University Press: Cambridge, USA.
  • Kahl, M.P. (1972). "Comparative ethology of the Ciconiidae: The wood storks (Genera Mycteria and Ibis)". Ibis, 114: 15-29
  • Kahl, M.P. (1964). "Food Ecology of the Wood stork (Mycteria americana) in Florida". Ecological Monographs, 34: 97-117.
  • Kahl, M.P. (1968). "Recent breeding records of storks in Eastern Africa". Journal of East African Natural History Society and National Museum, 27: 67–72.
  • Kahl, M.P., and Peacock, L.J. (1963). "The bill-snap reflex: a feeding mechanism in the American woodstork". Nature, 199: 505–506.
  • Hancock, J.A., Kushlan, J.A., and Kahl, M.P. (1992). Storks, Ibises and Spoonbills of the World. Academic Press: London.
  • Kasoma, P.M.B., and Pomeroy, D.E. (1987). "The status and ecology of storks and the shoebill in East Africa". Colonial Waterbirds, 10: 221–228.
  • Langrand, O. (1990). Guide to the birds of Madagascar. Yale University Press: New Haven.
  • Parsons, J. (1977). "The effect of predation by fish eagles on the breeding success of various Ciconiiformes nesting near Kisumu, Kenya". Journal of Natural History, 11: 337–353.
  • Pooley, A.C. (1967). "Bird/crocodile and bird/hippopotamus commensalism in Zuzuland". Ostrich, 38: 11–12.
  • Rand, A.L. (1936). The distribution and habits of Madagascar birds. Bulletin of the American Museum of Natural History, 72: 143–499.
  • Schüz, E. (1957). "Das Verschlingen eigener Junger ( “Kronismus”) bei Vogeln und seine Bedeutung". Vogelwarte, 19: 1-15.
  • Sinclair, I., Hockey, P.A.R., and Arlott, N. (2007). The larger illustrated Guide to the Birds of Southern Africa.
    Struik Publishers
    : Cape Town.
  • Stronach, B.W.H. (1968). "The Chagana heronry in western Tanzania". Ibis, 110: 344–348.
  • Tree, A.J. (1978). "A visit to Makgadikgadi Pan in April 1974". Honeyguide, 109: 18–19.

External links

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