My picks from ScienceDaily

Teens Who Do Use Condoms Often Don't Use Them Properly:

A worrying number of young people who do use condoms don't use them correctly, so risking unwanted pregnancy or infections, reveals research published ahead of print in the journal Sexually Transmitted Infections. But a good relationship with their mothers seemed to be associated with correct condom use, the research showed.

Paleontologist Discovers South American Mammal Fossils:

Fossils of a new hoofed mammal that resembles a cross between a dog and a hare which once roamed the Andes Mountains in southern Bolivia around 13 million years ago was discovered by Darin A. Croft, assistant professor of anatomy at the Case Western Reserve University School of Medicine and a research associate at the Cleveland Museum of Natural History.

Pressure To Be More Muscular May Lead Men To Unhealthy Behaviors:

New research suggests that men feel pressure to have muscular bodies, and that influence can lead some to symptoms of eating disorders, pressure to use steroids, and an unhealthy preoccupation with weightlifting.

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"Instead of seeing a decrease in objectification of women in society, there has just been an increase in the objectification of men. And you can see that in the media today," she said.

Light Guides Flight Of Migratory Birds:

Songbirds use multiple sources of directional cues to guide their seasonal migrations, including the Sun, star patterns, the earth's magnetic field, and sky polarized light patterns. To avoid navigational errors as cue availability changes with time of day and weather conditions, these "compass" systems must be calibrated to a common reference. Experiments over the last 30 years have failed to resolve the fundamental question of how migratory birds integrate multiple sources of directional information into a coherent navigational system.

Last autumn, Rachel Muheim, a postdoctoral associate in biology professor John Phillips' lab at Virginia Tech, captured Savannah sparrows in the Yukon before they headed south. She was able to demonstrate that the birds calibrate their magnetic compass based on polarized light patterns at sunset and sunrise.

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Polarized light is light that oscillates in one plane relative to the direction of propagation. At sunrise and sunset, there is a band of intense polarized light 90 degrees from the sun that passes directly overhead through the zenith and intersects the horizon 90 degrees to the right and left of the sun. Just as the sun location changes with latitude and the time of year, so does the alignment of the band of polarized light.

Muheim and Phillips argue that migratory songbirds average the sunrise and sunset intersections of the polarization band with the horizon to find the north-south meridian (geographic north-south axis), providing a reference that is independent of time of year and latitude. The birds then use this geographic reference to calibrate their other compass systems.

In other words, polarized light, the Sun and stars, and the geomagnetic field are all directional cues for migration, but polarized light appears to provide the primary reference system used to calibrate the other compass systems, said Phillips.

However, previous research had suggested a much more confusing picture.

Migratory birds are born with an innate magnetic compass preference that coincides with their species' migratory direction. Previous research suggested that before the migration period, songbirds are able to recalibrate the magnetic compass when exposed to a "conflict" between magnetic and celestial (including polarized light) cues, but during migration it appeared that the reverse was true, -- the magnetic field was used as the primary reference for calibrating the birds' other compass systems. But in a few experiments with birds during migration, the birds did recalibrate the magnetic compass.

When Muheim and Phillips did a literature review, they noticed a difference between the experiments of the few scientists who saw migratory birds recalibrate their compass and of those whose birds failed to recalibrate.

"It is important how you do the experiments. It turns out that the part of the sky that matters is just above the horizon," said Phillips. "In cue conflict experiments carried out before migration, birds were usually housed in outdoor aviaries in a rotated magnetic field, where they had a view of the whole sky, including the horizon. Once migration starts, however, scientists usually exposed birds in "funnel cages". This is so, after exposure to the cue conflict, the birds' directional preferences could be recorded; songbirds in migratory condition leave tracks or scratches on the sides of the funnel as they attempt to take flight in the migratory direction. A problem arises, however, because funnels block the lower 20 degrees of the sky. In the only two experiments (out of 30 or so) carried out during migration where birds were exposed to the cue conflict with a view of the horizon, they did recalibrate their magnetic compass -- just as was previously observed only in experiments carried out prior to migration."

Muheim's experiments proved that seeing polarized light cues near the horizon was the critical factor. "Once the right hypothesis came along, it all fit," said Phillips.