XINGU NATIONAL PARK, Brazil  As the naked, painted young men of the Kamayurá tribe prepare for the ritualized war games of a festival, they end their haunting fireside chant with a blowing sound  “whoosh, whoosh”  a symbolic attempt to eliminate the scent of fish so they will not be detected by enemies. For centuries, fish from jungle lakes and rivers have been a staple of the Kamayurá diet, the tribe’s primary source of protein.

But fish smells are not a problem for the warriors anymore. Deforestation and, some scientists contend, global climate change are making the Amazon region drier and hotter, decimating fish stocks in this area and imperiling the Kamayurá’s very existence. Like other small indigenous cultures around the world with little money or capacity to move, they are struggling to adapt to the changes.

“Us old monkeys can take the hunger, but the little ones suffer  they’re always asking for fish,” said Kotok, the tribe’s chief, who stood in front of a hut containing the tribe’s sacred flutes on a recent evening. He wore a white T-shirt over the tribe’s traditional dress, which is basically nothing.

Chief Kotok, who like all of the Kamayurá people goes by only one name, said that men can now fish all night without a bite in streams where fish used to be abundant; they safely swim in lakes previously teeming with piranhas.