This attractive pair from Colombia’s 1963 “Humboldt Centenario 1769–1859” airmail series honors the pioneering naturalist Alexander von Humboldt through finely engraved wildlife designs. The 5c stamp features the Unau (two-toed sloth) in soft brown tones against a turquoise field, while the 10c airmail value depicts the agile Marimba (spider monkey) in motion on a lime-green background. Printed by Staatsdruckerei, Wien, both stamps showcase crisp intaglio detail and classic mid-century Colombian thematic style. A desirable duo for collectors of Colombian airmails, zoological themes, and Humboldt commemoratives.