The following is taken from the following website:
Some dogs eat birdseed, a practice that can lead to fungal infections if the seed has fermented. Owners who feed the birds should clean up spilled seed before it gets wet and rots.
If your dog seems really ill and cannot hold down anything, I would take him to the emergency vet, or at least call them and ask about what your dog has eaten and see what they advise. It depends on how small or large your dog is, and what or where the birdseed was or has in it, that could have made your dog so ill. If your dog keeps vomiting too much, he will become dehydrated, so you may want to get him looked at, so you don't have to wait until Monday.
God bless and good luck!