An undercover investigation by the Humane Society of the United States found unsanitary and “inhumane” conditions at a Gettysburg, Pa., farm that supplies eggs to Costco, the animal welfare group said on Tuesday. Video collected at the farm, operated by Hillandale Farms, in April and May by someone “associated with” the Humane Society showed hens laying eggs in cramped cages with deceased birds. Broken eggs and dead chickens were on the floor. Hillandale provides eggs to some Costco stores under the brand name Nearby Eggs. The Humane Society called on Costco to provide a timeline for its promised transition to cage-free eggs. Costco, the third-largest retailer in the United States, did not have an immediate comment. Hillandale Farms said it was aware of the investigation, but did not comment further.