If climate change increases El Nino activity, as some scientists believe, the number of migratory songbirds that spend their summers in North American forests could decline significantly, suggests a study published today in the journal Science. Researchers from Dartmouth College and Tulane University found that El Nino climate cycles reduce the insect and caterpillar food supply available for black-throated blue warblers, leading to the birds producing fewer offspring during El Nino years. A separate study published this month in the journal Nature indicates that global warming is reducing the growth of white spruce in some Alaskan forests, contradicting some scientists’ predictions that warmer temperatures will spur tree growth. Meanwhile, U.S. environmental groups accused the Clinton administration yesterday of trying to weaken the Kyoto climate change treaty at international talks in Bonn, Germany.