The Andes mountains of Peru, which runs from the north of the country to the south, forms a very effective barrier against the humid winds from the Amazon basin, leaving the western slopes without rainfall needed to sustain extensive tropical forests. These dry slopes are dominated by cactus and small shrubs.
At least that’s the general rule; however in a few places with special climatic conditions, there are forests that look like the tropical eastern rainforests. The upper valley of the rivers Piura, Chira, La Leche and Zaña have these pockets of rainforest due to their proximity to Equator and due to the lower height of the Andes at these locations. This lack of height allows the passage of moisture-laden winds from the Amazon to these western slopes. These forests have unique bird life and are part of the center of endemism called the Tumbesian region.
Chachacomo forest in Lima
Further south, as move south away from the Equator and as the Andes gain altitude, forests become more scarce and are only present in the upper parts of valleys where Queñua (Polylepis sp.) forests are found at altitudes exceeding 3800 meters. Further down in the middle elevations of these valleys, between 2000 and 3000 meters, there are very few places that sustain deciduous forests dominated by trees like Chachacomo (Escallonia resinosa).
Purple Collared Woodstar | © Jean Paul Perret
Perhaps one of the best studied Chachacomo forests is the Zarate forest in the department of Lima. These forests were studied by the famous ornithologist Maria Koepcke in the 50s and 60s. Koepcke’s investigations led to the recognition of the fact that many bird species typical of the cloud forests of the eastern slopes extend their ranges to the western slopes of the department of Lima. Species such as Band-tailed Pigeon, Tyrian Metaltail, Red-crested Cotinga and the Fawn-breasted Tanager, typical of the eastern cloud forests have isolated populations in these western forests.
Pied-crested Tit-tyrant | © Jean Paul Perret
Koepcke’s investigations not only allowed us to know these extensions in the distribution of birds, but they also unveiled new species like the White-cheeked Cotinga discovered in the forest of Zarate, a place relatively close to Lima the capital of Peru in the year 1954, and the Russet-bellied Spinetail on the slopes of the department of Ancash.
Many endemic bird species live in these western slopes of central Peru, for example the Black-necked Woodpecker, Rusty-bellied Brush-finch, Rusty-crowned Tit-Spinetail, and Black Metaltail. All of these species can be observed along the Santa Eulalia Valley and the Zarate forest in Lima.
Rusty-bellied Brush-finch | © Jean Paul Perret
Bare-faced Ground-Dove | © Jean Paul Perret
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