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Blue whales singing with deeper voices
Posted by wideant in Plants & Animals on March 5, 2010
Blue whales, the largest animals on earth, are singing with deeper voices every year, but scientists are unsure of the reason.
Whale Acoustics is a company that specializes in recording the songs of blue whales off the coast of California. According to their President, Mark McDonald, they have many recordings of blue whales, but each year they have had to recalibrate their song detectors to lower frequencies. Possible reasons include noise pollution at sea, new mating strategies, and changing population dynamics, but none of these theories is convincing.
McDonald, along with John Hildebrand and Sarah Melnick of the Scripps Institution of Oceanography, have collected and analyzed thousands of recordings of blue whales from the 1960s onwards, from populations around the globe, and have found the tonal frequency of the songs has reduced by fractions of a Hertz every year. Read the rest of this entry »
Tropical birds waited for land crossing between North and South America: study
Posted by wideant in Plants & Animals on March 4, 2010
Despite their ability to fly, tropical birds waited until the formation of the land bridge between North and South America to move northward, according to a University of British Columbia study published this week in the Proceedings of the National Academy of Sciences Early Edition.
“While many North American birds simply flew across the marine barriers that once separated the continents, tropical birds, especially those in Amazon forest regions, began colonization of North America almost entirely after the completion of the land bridge,” says lead author Jason Weir, who conducted the study as part of his PhD at UBC.
“This study is the most extensive evidence to date that shows the land bridge playing a key role in the interchange of bird species between North and South America and the abundant biodiversity in the tropical regions,” says Weir, now a post-doctoral fellow at the University of Chicago. Read the rest of this entry »