Effects of a cold wave on an Amazonian avifauna in the upper Paraguay drainage, Western Mato Grosso, and suggestions on Oscine-Suboscine relationships

Abstract

The avüauna of the forested upper reaches of the Sopotuba River. in the upper Paraguay drainage just south of the Serra dos Parecís, proved a rnixture of central-Amazonian birds from just east of the Madeira Rtver and of birds of dry forests (Xingú-Tapajóz) or lower Andean forests peripheral to the southern Amazonian region . A cold wave that passed during the study period caused a major drop in insect activity and in the activity of inseci--eating birds and hummingbirds. Fruit-eating birds and "omnivores" (insect and fruit eaters) became relatively conspicuC'Ius. It is suggested that occasio· nal "clisasters" of the type of a cold wave inhibit specialized insectivores at this and other margins of Amazonian forests, and encourage hJgher percentages of omnivores . The previously noted tendency for oscines to replace suboscines at various types of neotropical forest rnargins ls reinterpreted as prlmarily due to declines of furnarioid suboscines (mostly forest-livmg insectivores> and their replacement by omnivf)rous tyrannoid suboscines anel by omnivorous oscines. The conventional theory that furnarioid suboscines are prirnitive and that they and other neotropical suboscines are being pushed into forests by recently immigrating oscines leads to two ecological anomalies: virtual absence of omnlvorous passerines in the carly Cenozoic an:i absence of seed-eat.ing passerines for much of the late Cenozoic . As alternate theory, that of separation of forest-edge suboscines by continental dritr followed by evolut.ion of forest-dwelling furnarioid suboscines in the New World, with open-country oscines either separated by the drift or entering South America early in the Ceno.zoic, removes both anomalies .In western Mato Grosso, a narrow penín-sula of Amazoni:an forest follows the Guaporé River southward and eastward on the south side of the Serra dos Parecís, a c2mpo or cerrado-covered plateau of some 500 meters'elevation. This forest península once re.ached east into the drainage of the upper Paraguay River, at least to the town of Barra de Bugres. East of Barra de BugrE.s, the remarmng vegetation is mostly dry forest grading into cerrado and pantanal. From Barra de Bugres westward. the foresr is rapidly being cut.Since birds of the Paraguay-drained eastern part of this forest had only been studied briefly by Natterer (in Pelzeln, 1867) and by Naumburg (1930) and coworkers, I welcomed an opportunity to look at birds there on an expedition of the Zoology Department of the Universidade Estadual de Campinas (UNICAMP) from 11 to 21 July, 1975. During our vísit, a major cold wave or friagem swept north, bringing frost and snow to souther~ Brazil and ending as floods in northeastern Br&,·il. This offered an opportunity to look at the effects of a friagem at the southern margin of the Amazonian forest, and contrast observations with previously reported minar effects of cold waves well to the north (such as Bates, 1962: 330).Here I gfve the species observed, and by means of daily counts of individuais and species eating v...

Estrutura trófica da avifauna na Reserva Estadual de Gurjaú, Zona da Mata Sul, Pernambuco, Brasil

“…Dados semelhantes foram constatados por WILLIS (1979), MOTTA-JÚNIOR (1990), ANJOS (1998ANJOS ( , 2001, ALEIXO (1999) (2001), o qual, verificou uma presença maior de onívoros em relação aos insetívoros. A variação nessas duas categorias pode ser explicada por um aumento na onivoria em áreas mais antropizadas, como fragmentos de mata, assim como em áreas cobertas por vegetação secundária ou exótica; a onivoria teria um efeito tampão contra flutuações no suprimento de alimentos (WILLIS 1976, D'ANGELO-NETO et al 1998, BLAMIRES et al 2001. Entretanto, ALMEIDA (1982) comenta que o número de espécies onívoras em geral é maior nas matas menos alteradas e o de insetívoros aumenta nas mais alteradas sendo este fato observado para o fragmento de Gurjaú.…”

Spatial and temporal patterns of bird species diversity in the Pantanal of Mato Grosso, Brazil: implications for conservation

“…brown (1986) observed that climate and resource instability and the abundance of large generalist predators in the floodplains favored large, mobile individuals, resistant to long dry periods and associated with aquatic environments. besides that, cold fronts that periodically occur in the pantanal during July and August could favor omnivorous species (Willis, 1976). in addition, the quantity of fish in the pantanal, which is among the greatest on the planet (conceição & paula, 1986), partially explains the present regional abundance of aquatic birds.…”

Taxocenose de aves em um remanescente da Floresta com Araucária no Sudeste do Paraná, Brasil

“…As relações Passeriformes/Não Passeriformes e Suboscines/Oscines indicam que o fragmento apresenta uma ornitofauna caracterizada por elementos silvícolas (cf. Slud 1976, Willis 1976, 1979 Biota Neotrop., vol. 10, no.…”