BARRINGTON — When the Caster family came home from vacation earlier this month, they found more than 15 dead birds littering the ground near their large birdhouse, along with evidence of a clear, tacky substance coating the shelter’s ceiling and the foliage below.

Yesterday, the animal rights organization Defenders of Animals said it would pay $1,000 to anyone with information leading to the arrest and conviction of the people responsible for the bizarre bird deaths at 19 Humphreys Rd.

Some type of spray adhesive was apparently used, said Dennis Tabella, the organization’s director.

“After traces of residue were found around the birdhouse, there is no doubt that this was a deliberate and sick act by an individual [or individuals] that need to be identified,” he said.

The state Department of Environmental Management is investigating. Spokeswoman Gail Mastrati said yesterday the residue is being tested for pesticides. Results are not expected for three weeks.

Homeowner Reed Caster said he’s puzzled by the material, which has remained tacky for two weeks and hasn’t been washed away by the rains.

“It’s almost like a gummy substance. It doesn’t have a scent to it. At first we though it was sap coming from the oak tree” from which the eight-chamber cedar birdhouse hangs, but then it became apparent that the substance had been sprayed upward by someone.

The shelter, shaped like an oversized Christmas ornament, hangs about 10 feet in the air.

“First thing in the morning, it was like a little bird city. Now it stands empty,” he said. “We tried getting [the sticky material] off, but it’s still pretty gummy and tacky. At some point I will power wash it.”

Tabella said the substance apparently doomed the birds by making their wings sticky. “I know there are sprays to glue things down at photo and copying places, but this sounds like something really strange.”

“It’s terrific someone would put up a reward,” Caster said. “It was such a stupid act.”

gemery@projo.com