Penguin found dead in latest animal death in German Zoo

Last month a 21-year-old sea lion named Holly was discovered after her skull was crushed

Two other penguins have gone missing from the zoo (Getty)

A German zoo is on high alert after a penguin was found dead and two others are missing, just a month after a sea lion is believed to have been killed in her pen.

Dortmund Zoo, in the east of Germany, has seen a string of mysterious animal deaths in recent months.

In the latest incident keepers found the one-year-old Humboldt penguin – born and raised at the zoo – lying dead in the flamingo pen on Monday. Two other birds from the same enclosure were then found to be missing.

"The loss breaks our hearts," Frank Brandstaetter, zoo director, told Associated Press.

A post-mortem is due to be carried out on the penguin, city administrators confirmed.

Last month Holly the 21-year-old sea lion was discovered with her skull smashed in and missing three teeth. Investigators later found a mysterious hole in one of the fences enclosing the zoo.

Authorities have not determined whether the incidents are linked, but police confirmed a possible connection was “part of our investigation.”

In the wake of the incidents , the zoo confirmed it had stepped up security.