Which animal did not attend Major's meeting in the barn in Animal Farm?

In Chapter One, the only animal who did not attend old Major's meeting in the barn was Moses, the raven, who "slept on a perch behind the back door."

Accordingly, old Major had a dream that he wished to communicate to the other animals. So, as soon as Mr. Jones (the farmer) was out of the way, all the animals made their way into the barn. The first of the animals to show up were the three dogs: Bluebell, Jessie, and Pincher. Next came the pigs, who settled down in front of the platform, where old Major was already seated.

The pigeons flew up to the rafters and the hens settled on the window sills, while the sheep and cows lay down behind the pigs. Then, Boxer and Clover, the two cart-horses, came in together. Next came Muriel, the white goat, and Benjamin, the donkey (the oldest animal on the farm). The last animals to enter the barn were the ducklings, the pretty white mare (Mollie), and the cat. It was only then that old Major began his speech.

Old Major essentially exhorted the animals to rise up in rebellion against their oppressor, Man. He did not tell them the details of his dream, only that he dreamed of what earth would look like once there were no more men around. Before the meeting adjourned, all the animals sang their new revolutionary theme song, "Beasts of England."