Backpack and Fingers are normal mates in so many ways.
They like hanging out together, getting a meal together and, as mates often do, going out together and looking for members of the opposite sex when the mood strikes them.
The pair just happen to be dolphins.
These are the observations of a group of scientists and volunteers who have been faithfully watching Perth's resident population of bottlenose dolphins.
A book released last night, put together by Murdoch and Curtin universities and aided by government and community groups, has given a rare insight into the behaviour of the animals.
It is the second such endeavour after the release of the first FinBook in May last year.
Tracking the movements and habits of 25 dolphins in and around the Swan and Canning rivers between last July and June this year, researchers found they tended to splinter into groups of "associates".
Backpack and Fingers were one such pair of associates, although they spent most of their time in Cockburn Sound and made only "occasional forays into the estuary looking for females".
Other allegiances included the one between two females, Daniele and Highnitch, along with the latter's calf, Highhope, and four males Hii, Arrow, Bottomslice and Blackwall.
"Like humans, dolphins are very social animals and tend to have long-term associates - so if you see one of these dolphins it is likely their associates will be nearby," Murdoch University dolphin expert Hugh Finn said.
The release of the book coincides with the decision to name the latest Swan River dolphin calf after Zari Ryan, who died from leukaemia in 2009 before she could fulfil her Make-A-Wish request to swim with dolphins.