Love on the rocks: Penguins celebrating Valentine's Day

An African penguin carries a heart shaped valentine handed out by aquarium biologist Piper Dwight to its nest at the California Academy of Sciences in

An African penguin carries a heart shaped valentine handed out by aquarium biologist Piper Dwight to its nest at the California Academy of Sciences in

Aquarium biologist Piper Dwight hands out heart shaped valentines to African penguins at the California Academy of Sciences in San Francisco, Tuesday,

Aquarium biologist Piper Dwight hands out heart shaped valentines to African penguins at the California Academy of Sciences in San Francisco, Tuesday,

An African penguin walks away with a heart shaped valentine handed out by aquarium biologist Piper Dwight at the California Academy of Sciences in San

An African penguin walks away with a heart shaped valentine handed out by aquarium biologist Piper Dwight at the California Academy of Sciences in San

African penguins compete for a heart shaped valentine handed out by aquarium biologist Piper Dwight at the California Academy of Sciences in San Franc

African penguins compete for a heart shaped valentine handed out by aquarium biologist Piper Dwight at the California Academy of Sciences in San Franc

SAN FRANCISCO (AP) — Penguins made a love connection at a San Francisco aquarium.

In what has become an annual Valentine's Day tradition, biologists handed out red felt hearts Tuesday to African penguins at the California Academy of Sciences.

The birds grabbed the hearts in their beaks and waddled around their rocky enclosure toward their nests.

Spokeswoman Kelly Mendez says it's often the male penguin who retrieves the heart and carries it back to his mate. The penguins use the felt for material in their nests, which helps reinforce the couples' bonds.

The activity is part of the academy's captive breeding program to help increase the African penguin population, which is endangered in the wild.