While the Shuar have long been resentful of encroachment and unwanted rule, as the 1599 uprising demonstrates, they're also amenable to visitors and what they consider fair trade. The 1921 National Geographic ethnography on the Shuar reported, "we found them a good natured people and very friendly to us" [source: Anthony].
This helped hasten trade between the Shuar who had tsantsas they considered useless following the ritual celebrations and outsiders who had guns they were willing to trade for the heads. The rate was usually an even exchange: one gun for one head [source: McGuiness]. The demand among Westerners for tsantsas led to an increase in intertribal warfare among the Shuar. Prior to Western interest in tsantsas, warfare among the Shuar was relatively infrequent; by the beginning of the 20th century, raids were carried out on a monthly basis [source: Jandial, et al]. The introduction of guns into Shuar culture only served to bolster this cycle.
The late 19th and early 20th centuries saw the peak in the production of tsantsas. While the increased demand is suspected to have led to an increase in head hunting, this increased trade also led to increased exposure to Europeans and contagious diseases. This, in turn, led to an increase in deaths among the Shuar, who suspected witchcraft, which in turn led to increased warfare. Between 1889 and 1911, the population of Shuar in one local area declined by 50 percent because of war [source: Rubenstein].
This demand for heads outside of the Amazon Basin also created a market for counterfeit tsantsas. In Shuar society, there is a remedy for a situation where a warrior successfully kills the person who bewitched and killed his relative but fails to take that person's head. In this case, a warrior may make a tsantsa from a sloth's head as a symbolic stand in. Sloth tsantsas were likely the first counterfeits to enter the global market, since they were authentic insofar as they had been made by Shuar tribespeople. In short order, however, these counterfeits were followed by others made of monkey heads, horse and goat skin and in some cases human heads taken from Ecuadorian morgues.
While private collectors and dealers made up most of the demand, museums commonly obtained tsantsas, by purchasing them, but more frequently as the recipients of donations of shrunken heads from collectors' estates. Museums too were subject to counterfeits; an audit conducted in the 1990s of the Smithsonian's collection found that only five of the 21 examined were authentic Shuar tsantsas [source: Aufderheide].
In recent years, holding counterfeit shrunken heads hasn't been the problem for museums; it's the authentic ones that are proving troublesome.