Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What's happening?
Shares of Pandora Media (NYSE:P) have fallen 18% this morning after the streaming music provider reported weak fourth-quarter results and offered underwhelming guidance for its first quarter.

Why it's happening
Pandora's $268 million in fourth-quarter revenue represented a 34% improvement over the year-ago quarter's result, but Wall Street analysts had expected $276.5 million. The company's adjusted earnings of $0.18 per share also fell below expectation of $0.19. Pandora's active-listener base grew to 81.5 million people, which was ahead of expectation for just 79 million active listeners. However, those listeners only streamed 5.2 billion hours of audio, well below the 5.38 billion hours Wall Street had forecast.

Looking ahead, Pandora for the first quarter expects to lose anywhere from $30 million to $35 million in adjusted earnings before interest, taxes, depreciation, and amortization, or EBITDA, on $220 million to $225 million in revenue. Full-year EBITDA is expected to range from $70 million to $80 million on annual revenue of $1.15 billion to $1.17 billion. Neither Pandora's first-quarter guidance nor its full-year outlook came near Wall Street's forecast for $243.6 million in revenue for the first quarter and $1.21 billion for the full year.