One of the nation's largest manufacturers of electric-fence insulators has changed their color from red to black because hummingbirds were electrocuted while trying to extract nectar from the insulators, which they mistook for flowers, the company said.

''The birds confuse the red plastic insulator as a food source,'' said Albert T. Berg Jr., chairman and chief executive officer of North Central Plastics Inc. in Ellendale, Minn. The company makes several million Red Snap'r insulators a year, he said, and although the color is being changed, the brand name won't be.

The red color initially attracted the birds, and the design of the insulators contributed to the problem, said Lee Pfannmuller, a zoologist with the Minnesota Department of Natural Resources in St. Paul.

''There had been reports of hummingbirds lighting on the wire, probing inside the insulator and being electrocuted,'' she said. ''To them, it looks like a nice red flower. Basically, it was the style and color combined that really caused the problem.''