Naturally seeping oil off the Southern California coast is taking a toll on seabirds, with dozens ending up coated in crude oil and tar, wildlife officials say. The naturally occurring oil bubbles up every winter but wildlife rescuers in recent weeks have seen an unusual influx of oiled seabirds stranded on the shore, with the region\'s main rehabilitation center in San Pedro having treated 140 birds since Jan. 1, the Los Angeles Times reported Wednesday. Hardest hit are common murres, penguin-like aquatic birds from Central and Northern California that spend most of their lives on the water, diving hundreds of feet below the surface to catch small fish and squid. \"The murres have been a new thing for us,\" Julie Skoglund, of the International Bird Rescue wildlife center in San Pedro. \"Over the last three years, we\'ve really seen a lot of them.\" The murre population is growing and expanding south, scientists say, putting the football-sized birds at greater risk of diving into waters fouled by natural seepage. Last year, researchers found a new colony of murres on remote Prince Island in the Channel Islands, the first time murre chicks had hatched there since 1912. \"That is a risky little zone there off the Santa Barbara coastline,\" said Josh Adams, a seabird biologist with the US Geological Survey\'s Western Ecological Research Center in Santa Cruz. \"There\'s substantial amounts of oil that surface that could pose a threat because of the proximity to the new breeding ground.\"