"Dolphin woos with wood and grass"

The BBC reports that "A South American river dolphin uses branches, weeds and lumps of clay to woo the opposite sex and frighten off rivals, scientists have discovered.
Researchers observed adult male botos carrying these objects while surrounded by females, and thrashing them on the water surface aggressively.
Writing in the journal Biology Letters, they say such behaviour has never before been seen in any marine mammal.
The boto lives in only two rivers, and numbers are thought to be declining.
A group of British and Brazilian researchers studied the dolphin's unique courtship behaviour over three years in the Mamiraua Reserve, a flooded rainforest area on the Amazon.
"You see them coming up with bits of wood or lumps of rock in a very ritualised manner," recalled Tony Martin from the Sea Mammal Research Unit at St Andrews University.

"Quite often they'd slowly come up above the surface in a vertical posture holding this stuff in their mouths, then sink down rotating on their own axis.
"They would also throw it or smash it against the surface, and it does appear that the waving around and bashing is to impress the ladies; but at the same time there's a lot of aggression between adult males, and we have to infer that's part of it."
Professor Martin's group established that rock carrying and branch thrashing were almost exclusively the preserve of adult males, and that they did it more when lots of adult females were present.
Although the males were more aggressive towards each other at these times, they were never seen to hit each other with the rocks or plants...

This research stemmed from a larger project, Projeto Boto, aimed at conserving the Amazon dolphin and its habitat.
River dolphins are among the most threatened of all cetaceans; the baiji, a native of the Yangtze in China, may already have gone extinct in the last two years, while numbers of the Indus or blind river dolphin of South Asia are believed to be down to around the 3,000 mark.

Compared to these species, the South American dolphin is in good health in its traditional haunts along the Amazon and Orinico rivers. The IUCN Red List of Threatened Species suggests "there are probably tens of thousands of botos in total".
But the future does not appear secure. The Red List concludes that the boto is threatened by dams (causing fragmentation of their habitat) and pollution, such as from mercury used in gold mining..."

Here is the rest of the story.