Albert Barnes Commentary Exodus 16:13

"And it came to pass at even, that the quails came up, and covered the camp: and in the morning the dew lay round about the camp." — Exodus 16:13 (ASV)

Quails - This bird migrates in immense numbers in spring from the south: it is nowhere more common than in the neighborhood of the Red Sea. In this passage we read of a single flight so dense that it covered the encampment. The miracle consisted in the precise time of the arrival and its coincidence with the announcement.