The London Aquarium is hoping to welcome its first brood of baby penguins, as a new colony of birds begins its first mating season.
But keepers have reported tiffs betwen rival males.
Penguins give their mates pebbles as a sign of affection - but other birds have been swiping them from the nests.
Aquarist Haley Clark says that collecting the pebbles is "like giving your girlfriend chocolate."
She said: "The male works out where he wants his nest and that is when he starts collecting pebbles. The female will join in as well after he has given her a few pebbles to place in the nest how she wants it."
But sneaky males sometimes steal stones from other birds' nests.
When that happens, they will run over "pretty sharpish and tell them where to go," Ms Clark adds.
"It can get a little bit aggressive but they generally back away very quickly."