The narrator in this case was our old friend, Fritz W. Up de Graff, the author of Head-Hunters of the Amazon (1921). Astute readers may remember him as the witness of some unusually large anacondas. The incidents played major roles in the book, and so are the ones most likely to be exaggerated. It is only fair to mention, however, that the last incident was inserted in the middle of a separate account of a river trip, and was quoted directly from his journal.
The point to be made is that the incident of the rainmaker did not play a similar prominent part in the story. There was no chapter on "the remarkable powers of a rainmaker". Rather, it was described piecemeal as the action developed in the account of a head-hunting raid. It was not the sort of thing you would expect to have been invented.
To set the scene, I shall quote the author's own comments.
Among all the Jívaro tribes the medicine-man is omnipotent but short-lived. He lasts as long as his prophecies are not too disastrously wrong. Sooner or later, he leads his people (of whom he is virtually chief) into disaster, having made a bad guess, and is lynched by those who before followed his every word.The medicine man in question, Tuhuimpui, plus a huge party of his Antipa tribesmen, along with many Aguarunas, all in canoes, had joined Up de Graff and his small band of comrades when the latter had turned off the Marañon River (the headwaters of the Amazon) into the Santiago River. In fact, they couldn't get rid of them. Coveting the white men's trade goods and presents, they accompanied them for several weeks, always friendly, but with treachery always on the cards. After a while, however, they apparently decided that the heavily armed white men were not going to relax their vigilance and so, since they were moving into the territory of their hereditary enemies, the Huambisas, they might as well go in for a bit of head-hunting.
It was on 26th October, 1899 - in fact, just three days after their encounter with a huge anaconda - that the Indians happened to discover a piece of charred wood, evidence that the Huambisas were somewhere in the vicinity. Having halted on a sandbar for the midday rest, the Indians collected branches from a small tree, stripped off some of the berries from the twigs, and planted the branches in the sand parallel to the river.
Tuhuimpui, it should be explained, had managed to acquire a basic familiarity of the Quechua language, as had Up de Graff himself. Indeed, the Jívaros referred to it as the "white man's language" although, strictly speaking, it was the language of the Inca empire.
Tuhuimpui strolled up to me unconcernedly. "We are going to make it rain," he said simply. "I hope you will not bring down enough to drench us and our cargo," I said with mock solemnity. "Never fear," came his grave answer; "only a light shower. To-night it shall rain and thunder and blow, but before we summon the storm, we shall build you a house."They planted some more branches, then put the berries into snail shells and cast them into the water with a lot of chanting and solemn gesture. Then they all departed in their canoes. Within half an hour, a small cloud mysteriously appeared, to provide the gentlest of sun showers. Considering that the rainy season was not expected till the middle of January, and that the sky had been perfectly clear for the past three weeks, the author thought this might have been stretching the long arm of coincidence a bit.
It turned out that the aim of the procedure had been to check for the approval of Yacu-mamam, the god of rain and rivers. If he had withheld the rain and left the sticks to wither and die, they would have known that the raid would have proved unsuccessful. Now Tuhuimpui began to boast. They would collect many heads. But that evening there would be thunder, lightning, and a great wind.
By six in the evening they found the mouth of a stream, invisible from the main river, where the Huambisas would have been camped. A scouting party was sent out. Meanwhile, the rest of the party camped on the opposite bank of the Santiago. Up de Graff gives a long description of the preparation, the concealment of all traces, the application of war paint, and how shelters were constructed in preparation for the coming storm, the small party of whites sandwiched between the two tribes.
And while the savages were performing a war dance around the fires, the storm struck with incredible fury. It lasted a mere half an hour, but during that time there was thunder, lighting, torrents of rain, and a wind so fierce that they had to post a sentry outside their shelter to warn them of falling branches.
The following day the head-hunting raid took place. It is far from obvious why it was necessary to invoke a storm beforehand. Perhaps it was needed to keep the branches on the sandbar alive.