Very interesting...

[observe]

During the mating season, the female sits on a nesting ring while the males searches the entire beach for the pebbles looking for the smoothest one to present to their chosen female.
Once a pebble has been selected, the male penguins presents the pebble as a token of love to the chosen female and if she takes the pebble and places it on her nest then she has accepted that penguin as her mate.

 

[Ole Bally]

Little known fact is over 80% of bird species are monogamous!

 

[Wheels]

The same thing worked for me. The stone was called a diamond. Just doing my part in keeping the RSA economy going.

 

[observe]

jerome, i hope the picture link is showing now
it's showing this side

During the mating season, the female sits on a nesting ring while the males searches the entire beach for the pebbles looking for the smoothest one to present to their chosen female.
Once a pebble has been selected, the male penguins presents the pebble as a token of love to the chosen female and if she takes the pebble and places it on her nest then she has accepted that penguin as her mate.