This Month in Photo of the Day: Animal Pictures

A reef manta ray dwarfs a researcher in the waters off of Nusa Penida, near Bali.

"On one special day we encountered dozens of reef manta rays feeding at the surface in Nusa Penida," Marine Megafauna Foundation cofounder and National Geographic explorer Andrea Marshall says. "When these giant animals feed they are distracted, and snorkelers can approach them quite closely without disturbing them. It is almost like they go into a trance.

"This individual spent about a half an hour with us, in quite shallow water, weaving in and out between us while feeding on densely concentrated plankton in the surface waters," she says. "As it approached me it reared up a bit and flashed its ventral surface (belly) at me, giving me a glimpse of its natural spot patterning on its underside, which we use to identify between different rays."

Marshall and her team recently created Manta Matcher, an automated online manta ray database. It "stores the patterning of each manta ray sighted across the world and automatically checks for a match every time a new entry is uploaded," Marshall says. "This system will allow researchers to follow the lives of these elusive animals and learn more about their movements and behavior over time."