What causes babies the need to burp?

Swallowing air. All humans burp. Its a fact of life. We swallow air along with our food and when we swallow a lot, some of it may come back out in the form of a burp. You only notice in a baby because they arent good at it and so it stands out more dramatically than in older kids.
Swallowed air. Babies often swallow air during feeding. Depending on your baby you should burp between sides (if breastfeeding) or about halfway through if bottle feeding. This removes the air from the baby's stomach and allows them to finish eating comfortably. You want to make sure that at the end of a feeding the stomach is filled with milk not air!