Changes in Understory Avifauna Along the Sinnamary River

Along the Sinnamary basin in French Guiana (South America) a succession of forest types occurs from the Ridge forest at the mouth of the river to the primary rain forest on the slopes of the narrowing valley 100 km to the south but only 35 m above sea level at the upper part of the dam reservoir of Petit-Saut.

The aim of the present work was to determine the relationship between bird community structure and river zonation.
This study will point out the variations in species richness and trophic structure for understory avifaunas in four forest habitats of the Sinnamary basin :

1) Sinnamary river mature rain forest: slopes of the valley at less than 100 m from the Sinnamary river and at 100 km of the mouth ; 2) Secondary forest (25 km from the mouth): from clear cuts at various stages of growth;
3) Riparian forest on wet, seasonally flooded bottom flats;
4) Ridge forest: close to the mouth of the river on sand Ridges.

Understory avifaunas for these habitats are compared each other as well as with those of mature primary rain forest habitats found outside the Sinnamary basin.

Cumulative curves, daily activities and biomasses are not significantly different between habitats. However, the principal component analysis shows marked differences in understory bird community composition between these habitats. The habitats are ranked in order of their distance from the sea along the Sinnamary River.

The Sinnamary river mature rain forest understory bird composition is similar to that of the reference primary forest. The highest diversity for gleaning insectivore and frugivorous species was found in the Sinnamary mature rain forest.
The Secondary forest had the highest number of species captures. The Riparian forest was characterised by a relatively high number of gleaning insectivores and a lack of terrestrial insectivores, granivores and nectarivores.
The Ridge forest was markedly different from the other habitats; only ten species found in this habitat were present in at least two of the other forest types, 20 species were unique to this habitat, mainly Picidae and nectarivores.