The once-endangered California brown pelican is in trouble again.
The number of breeding pelicans has plunged drastically.
An annual survey completed last month looked at breeding colonies in Mexico's Gulf of California, where 90 percent of the population nests. It found that this year, areas that typically host hundreds or thousands of nesting pairs sometimes held none at all, according to a statement Monday from the University of California, Davis.
The reason could range from food problems to changes in ocean temperature.
The California brown pelican was declared an endangered species in 1970 after being pushed to the brink of extinction by the pesticide DDT. It rebounded by 2009 but last year scientists said many birds were starving because their food supply -- sardines -- had crashed.