On this week's show: Do comets have seasons? And a roundup of daily news stories.

On this week's show: The energetics of high-altitude bird migration and a roundup of daily news stories.

On this week's show: Fighting worms to battle microbes and a roundup of daily news stories.

On this week's show: Measuring the success of massive open online courses.

The breakthrough of the year, readers' choice, and the top news from 2014.

Untangling the bird family tree and a daily news roundup.

On this week's show: When eels attack and a news roundup.

Meteorite hunters and a daily news roundup.

Sex in the brain and a daily news roundup.

Tracing the contributions of hippos to ecosystems and a daily news roundup.