"Criminal" penguins are rife at the London Aquarium, with mating season causing a spate of pebble pinching amongst the bird community.
Subterfuge and skulduggery is the Gentoo penguins' prerogative, as those with the best nests are most likely to secure a partner.
With a stealthy glance over their shoulders, the black and white burglars quickly waddle to their neighbours' nests, steal a stone and scurry back to their own breeding ground.
But as the number of burglaries increase, the gentoos have sensed something's fishy about the behaviour of their fellow colony members.
The penguin's attitude has turned icy, as if they notice a rival moving in to plunder their pebbles they quickly run back to defend their nests.
Smooth pebbles are "like gold dust" because they are easy to pick up and comfortable to lie on, according to those who tend to the birds.
Hayley Clark, aquarist at the Sea Life London Aquarium, said extra pebbles had to be put into the enclosure after burglar Vladimir has conducted daily robberies on surrounding nests.
She said: "Some of them are a little bit more tricky than the others, they keep an eye out for the owner of the nest before stealing. A couple of them will just run straight to a nest and will be chased off straight away.
There are ten penguins in the colony at the London Aquarium. Males declare their interest in a female by selecting and presenting a "love token" in the form of a pebble to their chosen female.
If it is accepted, the couple then begin collecting more pebbles to line their doughnut-shaped nest.
The birds build their stone nests to elevate and protect their eggs.
"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.
"It is like giving your girlfriend chocolate."
Ms Clark added that there has been "a few tiffs" over pebble thefts. "They will run over pretty sharpish and tell them where to go," she said. "It can get a little bit aggressive but they generally back away very quickly."
No eggs have been seen yet but breeders are hoping that a few will turn up in the next few weeks.