Wildlife rehabilitation facilities in California counties such as Monterey have admitted hundreds of sick brown pelicans since mid-May, according to the California Department of Fish and Wildlife.

The California brown pelican, which is a protected species, began arriving in care centers from Monterey down to San Diego on May 13, the CDFW said. The birds arrived emaciated and some had fractures or secondary injuries. Preliminary post-mortem examinations show starvation as the cause. No diseases or toxins were detected in the birds, nor was avian influenza.

CDFW estimates that 700 pelicans came into rehab centers for care, with 130 of them gaining weight, demonstrating normal behaviors and then being released. More pelicans are set to be released in the coming weeks as well.

The factors that contributed to the pelican’s starvation are still being investigated. According to CDFW, pelicans primarily feed on anchovies, but anchovies are currently abundant. One theory is that prolonged periods of unusually strong winds in late April and early May could have interfered with their ability to forage. Also, CDFW notes that pelican populations have been increasing, so competition for food resources might be a factor. The department will continue to investigate until they find the answer, scientists said.

The department is asking people who encounter dead pelicans to notify the CDFW’s Wildlife Health Laboratory and fill out a mortality reporting form.