Bread for the birds on Shabbat

Is it permissable to give left over challa to animals such as birds? My family and I are never able to finish it before it starts to go stale so instead of throwing it out I was wondering if it was allowable to feed it to animals on Shabbat?

The rule regarding the feeding of animals on Shabbat is as follows: Animals that man is obliged to feed - anyone can feed. Animals that can feed themselves - one may not feed them at all. The Shmirat Shabbat Kehilchata though allows one to shake the tablecloth outside even though the birds will eat the crumbs. (of course only if there is an Eruv.) Rabbi Chaim Shreiber