The population of a threatened seabird that nests in old growth forests in the Pacific Northwest has fallen almost 30 percent in last decade, researchers said. Federal conservation efforts have been unsuccessful in reversing or even halting the decline of the Marbled Murrelet, a release from the American Bird Conservancy said Friday. The birds nest in tall trees in old-growth forests in Washington, Oregon and California, and authors of a study on the birds said the loss of nesting habitat has been a major cause of the murrelets\' decline over the past century. The study, published in the journal The Condor, said Marbled Murrelet numbers in five different study areas fell sharply from 2001-10, from a total count of roughly 22,200 to about 16,700. \"This study confirms the fears that many conservationists have held for years,\" Steve Holmer, a policy analyst for the American Bird Conservancy, said. \"By showing that the Marbled Murrelet is still in sharp decline, the study emphasizes the need for stronger, more aggressive conservation measures.\" The Marbled Murrelet was listed in 1992 as threatened under the Endangered Species Act.