In temperate regions of the world, seeds are only available seasonally, so are not a dependable food for birds. In the spring and summer there are none and then in the autumn there is a glut. A single oak tree can produce 90,000 acorns a year, but lots of animals eat them besides birds so a jay will have to collect acorns quickly before others grab them all. A jay can carry nine in its crop and one in its beak. It stores the ones it cannot eat by burying them - as many as 3,000 in a month. When winter comes, it will remember exactly where most of them are.