More from the rabbit hole that is Pitt Rivers Museum.
“These shrunken heads, or tsantsas, are from the densely forested Upper Amazon region between Peru and Ecuador. The Shuar, Achuar, Huambisa, and Aguaruna peoples made them.
Traditionally, men were encouraged to take enemy heads to prove their manhood and to avenge the death of relatives. When raids took place on closely related groups the heads of sloths or monkeys would be substituted for human heads. Several of these examples are sloth heads.”
“English explorers collected shrunken heads because they saw them as exotic curiosities. These tsantsas were collected between 1871 and 1936. There was such demand for shrunken heads by museums and private collectors that some were made for sale from the heads of people who died naturally. Many monkey and sloth substitute heads were also sold.
The practice of taking or shrinking the heads of enemies ended by the 1960s. These peoples still live in their homelands by hunting, fishing, and horticulture as they always have. They fight against development and its affects upon them instead of enemy tribes.”