LIVERMORE (CBS SF) — Alameda County Supervisors approved an extension for permits for older model wind turbines on the Altamont Pass that environmentalists say could cause more bird deaths.

Altamont Winds was seeking a three-year extension on more than 800 turbines that are 20 years old or more. The county is in the process of decommissioning the old turbines for newer models that are not as lethal toward birds such as eagles, owls and hawks.

Audubon California maintains the three-year extension would result in more than 1,500 bird deaths from getting caught in the windmill blades.

Altamont Winds says it needs more time to replace the turbines and needs them to operate at capacity in order to help pay for their replacement.