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In the marshes of the Alto Tietê

New bird species is the first to occur exclusively in areas of the state of São Paulo

Female São Paulo Marsh Antwren (Formicivora paludicola)

Bruno RennóFemale São Paulo Marsh Antwren (Formicivora paludicola)Bruno Rennó

Some twenty small marshes around the headwaters of the Tietê and Paraíba do Sul rivers, 50 to 100 kilometers from the city of São Paulo, are the only known habitat of Formicivora paludicola, the first bird species that occurs only in the state of São Paulo. In no other preserved area of Atlantic Forest in Brazil has there been any record of specimens of the São Paulo Marsh Antwren, the popular name for the species, which was described by researchers in the December issue of the journal Revista Brasileira de Ornitologia. “Birds endemic to only one state are rare,” says Luís Fábio Silveira of the University of São Paulo Zoology Museum (MZ-USP), one of the paper’s co-authors. “Nature does not honor political boundaries created by man.” Antwrens usually live in pairs, a male and a female, and have a limited flight autonomy of just 25 meters. They never leave their marshy environment, where they hop back and forth between the leaves and stalks of cattails, a typical plant of marshes and floodplains.

Finding a new species of bird—the most frequently studied animal in the world of biology—east of this major metropolitan area of Brazil was a great surprise. This fragile antwren, measuring 11 centimeters (cm) long and weighing 9 grams on average, feeds on insects and lives at mid-level in the vegetation of isolated marshes located within the land areas of the municipalities of Mogi das Cruzes, Salesópolis, Biritiba-Mirim, São José dos Campos and Guararema. These marshy areas lie at the headwaters of the two rivers, at elevations of 600 to 760 meters above sea level. The new bird belongs to the family Thamnophilidae, which consists of 226 species (antwrens, antbirds, antvireos) and 46 genera. With the addition of the São Paulo Marsh Antwren, the genus Formicivora now includes nine species.

But in addition to making ornithologists happy, the identification of this little winged resident of the marshes around Mogi das Cruzes also brings cause for concern. The São Paulo Marsh Antwren is in serious jeopardy of imminent disappearance. Having been only just discovered, it can already be considered “critically endangered,” the final category before a species is declared extinct or nearly so, under the criteria of the International Union for Conservation of Nature (IUCN). Studies by Silveira and Glaucia Del-Rio, his Master’s student, indicate that there has been an enormous contraction of the marshy areas that served as habitat for the bird, owing to the expansion of urban centers, as well as rural and industrial activities, in eastern São Paulo State. “We estimate that the total population of antwrens today is 560 to 620 specimens,” says Del-Rio. “Our calculations indicate that the size of the present-day area of occurrence of the species (taking into account all the marshes where it has been found) is 1.4 square kilometers”—a land area more than a thousand times smaller than the size of the city of São Paulo.

According to maps from the São Paulo Geographic and Geological Commission consulted by Del-Rio along with Marco Rêgo, between 1885 and 1905 there were over 410 km2 of marshes and floodplains around the Tietê and Alto Paraíba do Sul rivers, of which 300 km2 exhibited the features necessary for hosting the species. “It is practically certain that the antwren existed within the city of São Paulo in the not-too-distant past,” Silveira says.

036-041_Aves_217-2Sister species
The new bird looks similar to its sister species, Formicivora acutirostris, popularly known as simply the bicudinho-do-brejo, or Marsh Antwren, which occurs along the coastal strip that extends from Paraná to northern Rio Grande do Sul. But the São Paulo Marsh Antwren has features that distinguish it anatomically and genetically from its closest relative. The thighs and underparts of the males are black, darker than those same parts in the Southern antwren. The back is dark grayish-brown, also distinct from that of its sister species. The exposed upper ridge of its beak is smaller than that of the more Southern-occurring bird. The females of the two species also have distinct appearances. Molecular studies indicate that the most recent common ancestor of these two types of antwren likely lived during a time prior to the emergence of modern man. “We analyzed mitochondrial DNA from the two species and estimated that, evolutionarily speaking, they separated between 250,000 and 640,000 years ago,” Silveira says.

A little over nine years passed between the discovery of the first São Paulo Antwrens and the official description of the species. The first person to record the sounds of specimens of this bird was Dante Renato Corrêa Buzzetti of the Center for Ornithological Studies, an NGO in São Paulo, one of the authors of the recently published scientific paper. On October 4, 2004, during an excursion through a vast marsh in Mogi das Cruzes dominated by cattails and other aquatic plants, Buzzetti came across a female and a young adult of what he judged initially to be specimens of F. acutirostris, the Southern antwren. Intrigued by the presence of these rare animals in the region, he returned there the next day, caught sight of a black-bellied antwren and collected two specimens of the bird.

A short time later, Silveira also found the bird in marshes in the municipality of Biritiba-Mirim. In February 2005 he discovered a population of approximately 100 antwrens in that location. “The problem was that the area was about to be flooded by construction of a dam,” the MZ-USP ornithologist recalls. “We had to quickly put together a plan to remove the birds from there and reintroduce them into locations with the same features.” Seventy-two antwrens were rescued and relocated in half a dozen marshes in the region. This is the reason why today there are places where the bird occurs spontaneously and naturally, and others where it was introduced (see map). If the marshes of the Alto Tietê continue to shrink, however, the São Paulo Marsh Antwren could disappear altogether.

Distribution, habitat and territory size of the São Paulo Marsh Antwren (Formicivora SP. Nov.) (nº 2011/16251-7); Grant mechanism Master’s degree scholarship; Principal Investigator Luís Fábio Silveira; Grant recipient Glaucia Cristina Del-Rio; Investment R$43,360.02 (FAPESP).

Scientific article
BUZZETTI, D.R.C et al. A new species of Formicivora Swainson, 1824 (Thamnophilidae) from the state of São Paulo, Brazil. Revista Brasileira de Ornitologia. V.21, No. 4, p. 269-91. Dec. 2013.