Hippos enjoy spring sun at Philadelphia Zoo

PHILADELPHIA (WPVI) -- It's a sure sign of spring when the hippos come out to play.

PHOTOS: Hippos come out to play at Philadelphia Zoo

The Philadelphia Zoo's female hippos, Cindy and Unna, basked in the spring sunshine Thursday morning.

The Philadelphia Zoo's female hippos, Cindy and Unna, basked in the spring sunshine Thursday morning.

Visitors gathered to watch the two take a dip in their outdoor pool for the first time this season.