Seeds soaked in water for germination disappear

Growing plants from seeds is often difficult because pests and others may eat the seeds.
Since birds are eating the seeds kept outside the house in the balcony , the seeds were put in a plastic container and soaked in water.
For the first few days,the seeds remained in the plastic container.
After a few days, the seeds have completely disappeared, there is no trace at all. In future,the container with the seeds should be covered to prevent loss of seeds.