Federal wildlife investigators who visited the BrightSource Energy plant last year and watched as birds burned and fell, reporting an average of one "streamer" every two minutes, are urging California officials to halt the operator's application to build a still-bigger version.

"We take this issue very seriously," said Jeff Holland, a spokesman for NRG Solar of Carlsbad, California, the second of the three companies behind the plant. The third, Google, deferred comment to its partners.