Bird migration and regional circulation in the Pantanal

Jabiru mycteria, Fazenda Ypiranga, Pocone, Mato Grosso / Brazil

Whereas long-distance bird migration for aquatic bird species is roughly understood there are other movements of birds between especially the lower Paraná River valley wetlands in Argentina, and the south Brazil/Pantanal wetlands which are far from clear.

Besides the fact, that the global patterns of Summer/ Winter north and south of the equator determines the arrival and departure of arctic migrants and Patagonian guests, there are two major inherent factors which drive birds moving in and out the Pantanal. The one is the regular change in flooding and dryness or even droughts. The other factor is the different food mix embedded in that pattern of seasonal flooding. Whereas most birds move in with the floods in September/ October others move in when the floods retreat using food resources e.g. on small pools left after the waters has covered the most part of the Pantanal.

A good example are the Jabirus, Jabiru mycteria, big storks, which are not present in the Pantanal during the flooding season. Obviously they move to higher grounds to sites outside the Pantanal area. Availability of food for the adult individuals to raise their young are the driving factor. The birds prefer low water levels, especially in lagoons and ponds, in order to obtain the food they can catch with their specialized beaks. Besides by watching for preys while walking they also hunt by tactile prey location, thanks to the sensible bill tip. The Jabiru feeds on various aquatic preys such as fish, molluscs, crustaceans, amphibians, snakes, even young caimans and insects.  They walk slowly in shallow water, regularly stabbing and pecking at preys with the bill. One of their fish species preferred are mussum fish (Symbranchus marmoratus), which can stay dormant and encapsulated in the mud throughout the dry season. They are reactivated by the humidity of the rain and start to swim again when the water rises in the rainy season. The Jabiru is a specialist in detecting and catching the dormant fish in the muddy ground of the dried ponds.

Another example of birds using the environmental conditions during the dry season are huge  concentrations in nesting sites in the gallery forest, to take advantage of the seasonal resources available. The breeding colonies are formed by hundreds of nesting birds, such as Wood stork (Mycteria americana), egrets (Snowy Egret, Egretta thula, Great White Egret, Casmerodius albus and the Capped Heron, Pilherodius pileatus) and the Roseate Spoonbill, Ajaia ajaja. In this gallery you will find some more examples of bird moving in the Pantanal or adjacent Southern Brazil or migrate to these wetlands.

In his article in Bird Conservation International, 4, „Migration and other movements among the lower Paraná River valley wetlands, Argentina, and the south Brazil/Pantanal wetlands“, Paulo de Tarso Zuquim Antas mentioned in 1994 that only for the Rosy-billed Pochard, Netta peposaca, a highly-prized trophy of hunters, some investigation was done until the 1970s. Consequently further research was done on Fulvous Whistling-duck, Dendrocygna bicolor. In the meantime bird migration and bird circulation within a wider area is much better understood.

Whereas Greater Yellowlegs, Tringa melanoleuca, Lesser Yellowlegs, Tringa flavipes, Solitary Sandpiper, Tringa solitaria, Semipalmated Plover, Charadrius semipalmatus, Pectoral Sandpiper, Calidris melanotos, Buff-breasted Sandpiper, Tryngites subruficollis and maybe White-rumped Sandpiper, Calidris fuscicollis are typical arctic migrants from Canada, Alaska and the northern USA patagonian migrants like Tawny-throated Dotterel, Oreopholus ruficollis or Rufous-chested Plover, Zonibyx /Charadrius modestus are widespread in lower Paraná river valley in Argentina; but these birds are already rare in south Brazil and are not recorded for the Pantanal.

The White-faced Ibis, Plegadis chihi occurs in the lower Paraná River valley wetlands, in the south Brazil of Rio Grande do Sul and in the Pantanal wetlands. This bird is truly migratory in the Pantanal, where it is observed from at least late May until October or even earlier (April until December; see Cintra and Yamashita 1990). No breeding is recorded in the Pantanal and these ibises must immigrate from more southern colonies, probably from Argentine. A nestling banded in Santa Fe province, Argentina, was found in August 1968 near Corumba according to Olrog 1971, confirming this movement. However, it is worth noting that other nestlings of the same colony were found in various parts of southern Brazil. The White-faced Ibis is found year-round in Rio Grande do Sul’s wetlands.

For many more birds like e.g. Black-bellied Whistling-Duck, Dendrocygna autumnalis, Bare-faced Ibis, Phimosus infuscatus and Limpkin, Aramus guarauna the picture of movements, short-distance migrations or regular circulation between different wetlands in South America is even less clear.

The wetlands of the central/southern portion of South America are among the world’s largest seasonally flooded areas. This is not only true for the huge Pantanal plain, but also for other big water systems in the central/southern portion of Brazil and adjacent northern Argentina. Whilst the Pantanal itself has an area of 158,592 square kilometers (almost 3 times the size of Switzerland), the Upper Paraguay River basin – supporting flows in the Pantanal – is much bigger.  Altogether the basin occupies 624,320 square kilometers. 61 %  of the basin lies within Brazil, 20 % in Bolivia and 19 % in Paraguay. 8 million people make their living within the fazendas, villages and cities in the basin on basis of the associated water resources. The Pantanal´s importance for aquatic bird species is almost unrivalled. The Paraguay River, the most important tributary of the Parana River, is almost a continuous wetland after its descent from the Central Brazilian Plateau highlands, forming the Pantanal in the upper valley and feeding a big floodplain south of it. The Parana is a river with rapid waters in its Brazilian portion, becoming a slow-water river with a large flood-plain when it enters Argentina and is joined by the Paraguay River. Rio Grande do Sul is the southernmost part of Brazil and enjoys big wetlands, too. These wetlands are not fed by major rivers.

In the focus of Bird-Lens are not only shots of the species of the Western Palearctic. Bird-Lens is also keen to enrich the range of pictures of birds you can find in other parts of the world.  The image of the Jabiru is only a first impression, what you will find in the gallery in the “Pictures Shop” very soon. Just give a message, if Bird-Lens could serve you with an image needed before the new pictures are online. The migration of birds of the Pantanal and the importance of more research might be the topic of a presentation at the Latin America Symposium held on the 7th of December 2012 in Bonn at the ZFMK.


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