Maguari stork
Kingdom
Phylum
Class
Family
Genus
SPECIES
Ciconia maguari

The maguari stork (Ciconia maguari ) is a large species of stork that inhabits seasonal wetlands over much of South America, and is very similar in appearance to the white stork; albeit slightly larger. It is the only species of its genus to occur in the New World and is one of the only three New World stork species, together with the wood stork and the jabiru.

Distribution

Geography

The maguari stork has a relatively wide distribution over much of South America, and occurs primarily to the east of the Andes. It lives in the Llanos of Venezuela and eastern Colombia; Guyana; eastern Bolivia; Paraguay; Brazil, but rarely in the Amazon and the north-east,); Uruguay and Argentina. The most southerly part of the range lies in the Chubut province. It more rarely occurs to the west of the Andes (e.g. in Chile) and probably does not breed there. It is a rare visitor to the Suriname coast from March until May and also been reported as a vagrant on Trinidad and Tobago.

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It is especially common and widespread in the Chaco of Argentina, which appears to be a popular destination for flocks of about 30-40 migrant individuals from the southern hemisphere part of the range that come from the south in winter to seek warmer temperatures. The stork is also common in Brazil, especially in the state Rio Grande do Sul, Paraguay and the Pampas of Argentina. It occurs seasonally and is common in the Pantanal of Argentina. Large numbers migrate to the Pantanal in the wet season, probably from the Parana Basin and Rio Grand do Sul. However, overall migration patterns for this species across its range have thus far not been determined exactly.

Its habitat largely comprises open lowland shallow-water wetland such as tropical wet savannah grasslands, marshes, mudflats, and flooded fields. It more occasionally frequents dry fields, but invariably avoids forested regions. Numerous maguari stork assemblages have been observed in their habitat during the dry season, where they forage in low-level bodies of water where prey is concentrated.

The maguari stork lives in sympatry with jabiru and wood stork where the ranges of these three species overlap, especially in the Venezuelan llanos. Of all American stork species, the maguari stork has the smallest geographical range.

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Maguari stork habitat map
Maguari stork habitat map
Maguari stork
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Habits and Lifestyle

Seasonal behavior
Bird's call

Diet and Nutrition

This stork has a markedly broad diet and is considered to be a generalist compared to the sympatric wood stork and jabiru. It feeds on fish, frogs, eels, earthworms, invertebrates, insect larvae, snakes, freshwater crabs, small mammals such as rats, and bird eggs. More rarely, it may take smaller birds; as one case has shown where a large, intact rail was discovered in the gullet of an individual from Patagonia. Despite the maguari stork's apparently generalist diet, one study from Brazil has suggested that this stork may actively target worm lizards (Amphisbaena ) as prey items. This may be because of the elongated body shape of such taxa that occupies a relatively small volume in the bird's stomach and hence can more compactly fit inside the stomach to optimise the bird's energy intake.

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The maguari stork preferentially forages in shallow waters about 12 cm deep, and more rarely at water depths of up to 30 cm. This may be because shallow waters harbour higher numbers of prey taxa, or are high in dissolved carbon and nutrients. This species is primarily a visual forager and its usual manner of hunting consists in walking slowly through wetlands with its bill close to the surface of the water, ready to seize prey encountered. It breeds early during the seasonal rains whilst the water in the wetland habitat is still clear from the fresh rainwater; so that prey items are more visible through the water and success of prey capture, especially as food for nestlings, is higher. However, this stork has also been observed to grope with its bill in the water, although this may be more common toward the end of the breeding season when water bodies begin to dry up and become turbid.

Especially during the breeding season, the maguari stork forages solitarily or in pairs. However, it feeds in larger aggregations outside the breeding season and often also in association with other wading bird species. The shallowness of these pools concentrates prey items, so that tactile foraging probably operates in this situation.

Although the maguari stork largely depends on shallow freshwaters as a source of prey, it has also been observed to forage solitarily on dry plains outside the breeding season where mice and toads (candidate prey) sometimes occur in large numbers. It also forages on dry, cultivated fields where invertebrates have probably been disturbed. During the evenings in the dry season from December until April, individuals form large assemblages around low-lying water features where prey density is high but prey abundance is not. Notably numerous assemblages of foraging maguari storks have been sighted in the Brazilian municipality Quissama during the dry season in October, where they congregate around shallow pools in search of food. The maguari stork's tendency to forage in both wetlands and dry lands reflects its generalist nature, whereas specialists such as the jabiru depend more on wetlands as a source of food and are sighted more frequently near to wetlands than the maguari stork.

In one study at half-hectare ponds in the llanos during the dry season, a flock of 90 maguari stork individuals were observed together with jabirus and wood storks. Because of limited prey, intra and interspecific competition inevitably occurs in such aggregations; often leading to kleptoparasitism. Maguari storks are mostly found to steal food amongst themselves, but jabirus also occasionally steal from them large prey items such as eels.

The maguari stork has also been observed to uplift cowhides in dry fields in search of potential invertebrate prey underneath. This occurs especially in the non-breeding season when large migratory flocks search for arthropods in the bushes and dry short grass. Some individuals also sometimes eat pieces of cow dung. Historically, one individual has been observed to swallow a cowhide whole.

Food brought to nestlings by their parents includes fish and eels, small mammals such as rats, and invertebrates. However, the proportions of these taxa differ between years depending on availability and the food brought to the nest for the young consists predominantly of aquatic organisms. Parents carry food to the nest as a large bolus in the throat. They regurgitate it onto the nest, whereupon it is picked up and eaten by the nestlings. Food is usually regurgitated in small parts for young nestlings, and as one large mass for older nestlings.

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Mating Habits

Many aspects of the maguari stork's reproductive biology and nesting strategies are unique to this species and are absent in other stork species. Such differences in breeding and nesting habits have probably resulted from strong selection pressures that would have led this species to become adapted to survive in its open lowland wetland habitat that it originally invaded.

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Breeding is highly synchronised with the onset of rain during the wet season, which usually lasts from May to November in the llanos of Venezuela. However, most breeding of the maguari stork happens from July to mid-September, which is earlier than breeding in both the sympatric wood stork and the jabiru. Individuals begin migration to the breeding grounds as the rains begin, although some individuals may migrate and arrive early just before the rains. Despite the lengthy wet season in the llanos, the nesting period in one year never lasts for over four months. Elsewhere in the stork's global range, the timing of the breeding season is slightly different and somewhat shorter. In north east Argentina for example, the breeding season extends from June to August; and in east central Argentina extends from July to October, with eggs probably being laid in late June and early July. On Isla Mexiana in eastern Brazil, the breeding season lasts only from August to September. The timing of onset of the seasonal rain is extremely variable across the maguari stork's global range, with rainfall beginning in some years as early as late March and others as late as June. The start of breeding is therefore correspondingly variable; and in Argentina, nesting may commence as late as August with late rains. In the llanos, breeders may lay eggs as early as late May following unusually early and heavy rainfall; whereas young breeders may lay eggs as late as October with late-arriving rain.

The clutch size is typically 3 or 4 eggs, with an average of 3.2 being reported. Eggs are laid on alternate days, so that hatching within clutches is highly asynchronous; with some young hatching up to a week apart. Incubation begins after the 2nd or 3rd egg is laid, is carried out by both parents, and lasts 29–32 days. The eggs are oval or subelliptical, and mean egg measurements are 75.19mm in length and 52.56mm in width; with maximum egg measurements of 77.4mm in length and 56.2mm in breadth having been recorded. The eggs are also said to be disproportionately small compared to the laying female's body mass.

Weight differences between different-aged siblings have been recorded as 500-1400 g. Egg laying is however highly synchronous between nests in a colony, so that relatively large groups of young from different nests fledge together in batches toward the end of the wet season. This may serve as an anti-predator strategy to dilute an individual's risk of being predated. As adults, male maguari storks become sexually mature at three years of age, and females at four years.

After three weeks of age, Maguari stork nestlings develop defensive behaviour if their nest is approached by an intruder; which is not known for nestlings of other stork species. They crouch forward, partially spread their wings and erect the black feathers on their head, neck and back; followed by a shrill, rasping scream and an attempt to grab a persistent intruder with their bill. In many other stork species, akinesia lasts throughout much of the nestlings’ early life, and the constantly white plumage makes them appear as eggs to potential chick predators. However, in maguari stork nestlings, akinesia ceases much earlier, and the unusual aggressiveness of the young has probably developed as a specialised anti-predator strategy in compensation for the young chicks’ inability to leave the nest due to their slow-developing hallux and the vulnerable position of the nest on the ground. However, at 25–35 days old, the hallux is sufficiently developed to allow the chicks to leave ground nests in search of food. Chicks also occasionally beg for food from their parents outside the nest, but parents have never been observed to feed their young outside the nest.

There appears to be little sibling rivalry in maguari stork nestings, with most nestling mortality being due to young falling out of nests containing 3-4 chicks; and egg mortality primarily through predation appears to be higher than chick mortality.

The large congregations of maguari storks in the pre- and post-reproductive periods are considered a reliable indicator that this stork breeds locally in the area in which the groups are sighted.

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Population

Population threats

The primary threats to this species are anthropogenic habitat disturbance and hunting for food. A common human disturbance occurs through habitat destruction via land reclamation from marshes for agriculture, which has occurred especially in southeast Brazil and may therefore evoke conservation concern for the species in this area. Claiming land for agriculture by digging canals, together with land filling and sewage discharges may also threaten dry-season foraging environments for maguari storks especially on the northern Rio de Janeiro coast. The maguari stork is vulnerable to nesting habitat destruction because it shows nest-site fidelity, and will continue to nest in the same place even after onset of recent anthropogenic disturbance. Use of pesticides may also adversely affect the health and breeding success of this species. The capture of individuals for food presents another survival threat and occurs particularly in the Southern Amazon and Venezuela.

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Natural enemies of this stork include boa constrictors and crested caracaras (Polyborus plancus ), both of which eat this species’ eggs. Both of these predatory species can probably also eat maguari stork chicks that are no more than a few weeks old. Many other potential predators such as jaguars, crocodilians, Pampas cats and maned wolves could also access ground nests. Although these animals are known to opportunistically feed on birds, no instances of predation on maguari storks have been hitherto recorded; but such predation is considered likely.

The maguari stork is potentially threatened in the Pantanal, which as well as being subject to considerable land reclamation for agriculture, has hosted increased operation of hydroelectric dams, especially in the Parana river basin. Dams retain much water during the dry season, so that natural water features downstream are more likely to dry out completely and thereby lead to a decrease in suitable foraging sites for this stork. Conversely, during the wet season, dams can lead to extensive flooding downstream caused by the release of a large volume of water at once that renders the storks’ usual foraging grounds too deep for them to stand in.

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Population number

The maguari stork is evaluated as being of least concern because it has an extremely large geographical range, and an apparently stable world population that is suspected to be very large. Despite local declines in some parts of its range, the population is not considered to be threatened on a global scale. However, even though this stork appears to be numerous throughout its natural habitat, census data are lacking and there appears to be no current estimate of the world population. This should be a new target of conservationists, and a clearer overview of this stork's world status could be aided by carrying out numerous aerial surveys of nesting areas.

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This stork may be especially vulnerable in the llanos of Venezuela. Its population declined strongly there in recent past decades starting from 1977 and less than 5000 individuals were estimated to live in this region through most of the 1980s. A potentially effective conservation strategy to help protect this stork's natural habitat in the llanos is the expansion and maintenance of cattle ranches in the savanna grassland matrix in preference to crop cultivation; because such ranches are similar in vegetation structure to natural grasslands. Another potentially useful conservation measure is the deployment of artificial nesting platforms to encourage nesting of maguari storks, as has been done for the white stork in Europe. Despite its relatively unthreatened overall status, the maguari stork should deserve closer global population monitoring to better safeguard it from future potential large-scale declines across its entire range.

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Coloring Pages

References

1. Maguari stork Wikipedia article - https://en.wikipedia.org/wiki/Maguari_stork
2. Maguari stork on The IUCN Red List site - https://www.iucnredlist.org/species/22697688/93630558
3. Xeno-canto bird call - https://xeno-canto.org/50307

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