Peru's arid forests and swallows

Chile is awesome, but more on that later. 

For three months this spring, I was in Pacora, Peru in the northern desert region. Because of the Andes, Peru has a huge rainshadow on the western side. Portions of it are sand as far as the eye can see, while other parts are dry tropical forest. Dry “forests” might be classified in the states as scrubland, as there is a lack of large trees (where you draw the line between a shrub and a tree might be important here), but no matter the name these areas are incredibly interesting and rare areas worldwide.

Bosque de Pomac Sanctuary, Lambayeque, Peru

During my time there, rains fell only twice and each was simply a light drizzle. Rain farther up in the mountains, which this area relies on for agriculture as it flows down the rivers were scarce as well because of the la niña event, therefore many fields went fallow this year. However, the forests teemed with birdlife and lizards. Endemism – the existance of a species in one place and nowhere else – is high in these areas, because of the narrow historic range (the Andes are close to the Pacific) and because of extensive human development in these areas.

White-tailed Jay, a dry-forest endemic

Historically, the Sican and other cultures lived in the area, growing what crops they could on the land and bringing seafood in from the coast. You can still find clamshells scattered around the ruins that were brought and eaten there 1200 years ago. Nowadays, the local economy gets by – certainly does not thrive – on farming rice and other water intensive crops by either damming rivers during the “wet” season and retaining the water or by pumping out the deep water table and irrigating that way. Additionally, they utilize some local resources – Acacia seed pods are harvested to make a sickly sweet syrup much like maple syrup (but as a New Englander, I feel it is inferior).

I was there to study the Tumbes Swallow, an endemic swallow to the area from Chiclayo to about the Ecuador border – basically 6 hours in a car. It exists only in the remaining dry forests and a few towns. Whether it has historically had higher populations, we don't know, but most of the dry forests in unprotected areas (and even in some protected areas) are exploited heavily for firewood – a necessity of life – by the local population. On a more positive note, within the national park of Bosque de Pomac, the Tumbes Swallows are thriving.

Tumbes Swallow fledgling, you would look that upset if you had a parasite on your face, too.

They belong to the genus Tachycineta, which includes species from Alaska to Tierra del Fuego and essentially everywhere in between. You are probably most familiar with the Tree Swallow or the Violet-green Swallow, the two members of the genus in the USA. The Tumbes Swallow is nothing like these, however. It is about half the size of a Tree Swallow and lives in deserts (most Tachycineta live near water).

It seems most likely that their water demands are met solely by the insects they eat, which is a difficult thing in that environment. In a normal water year, there are some mosquitoes around (and dengue), and a few other ariel insects. However, in the la niña year last year, almost no insects were present – the only ones around were these litte gnats that tried desperately to get in your eyes and mouth, probably for the water. How the swallows managed, I don't know, but they did – about 50% of the clutches fledged babies, and more would have if not for predation.

Lesser Nighthawk - a common desert species from the US to Chile

Normally, when a predator hits a nest box, we can usually deduce the culprit. In Chascomus and parts of the US, snakes will eat eggs or chicks. In Tierra del Fuego, southern House Wrens will steal the eggs and eat them, though occasionally just puncturing them and leaving them there with two little holes in them. In Bosque de Pomac, we had no idea what ate the chicks (eggs were never touched). We had two guesses: Peruvian Pygmy-owls, a tiny, day-flying owl, to which the swallows responded violently, or el raton de campo (literally, “the rat of the field”) a rat that would climb trees and may have eaten babies. Upon my return to this cool ecosystem in February I hope to figure out this mystery as well as another interesting phenomena occurring with the swallows – that they breed and molt at the same time, a very rare phenomenon in birds and even rarer in birds that feed on the wing.

Peruvian Pygmy-owl, red morph

Lizards, from tiny house geckos to gigantic tegus, were everywhere in the desert.

Pearl Kite, another raptor around the site that pissed off the swallows



Andre Burnier with the commenest species of bird observed: Black Vultures