Translation:Los pájaros cantan.
When to use articles is a mystery indeed! In general, if the subject is a broad, unspecified thing, like birds, life, love, etc. you use the article. It makes life easier if you can get the idea that it means "the" out of your mind, IMO. The article is often untranslated. I have asked my teachers (in Mexico, Argentina, and USA) about whether to use article or not in many situations, and the response is sometimes shrug o the shoulders and the Spanish equivalent of "Whatever!" :)