Researchers at a New York aquarium have documented beluga whales exhibiting behaviors consistent with self-recognition in mirrors. Two whales, Natasha and her daughter Maris, were observed performing various movements while examining their reflections in a two-way mirror over several hours. A study published in PLOS One reports that both whales displayed the key behaviors scientists associate with mirror self-recognition, a cognitive ability previously documented in humans, certain great apes, elephants, and dolphins. The test involves placing an invisible mark on a part of the animal's body only visible through reflection. If the animal investigates the mark while viewing its reflection, it demonstrates understanding that the reflection depicts itself.