oncidium and dendrobium leaves yellowing

[electric.chowder]

Since it's been nice outside here recently (upper 80's in the day and mid 60's at night) I've been leaving my orchids outside. My two phals are loving it, and one is growing a new leaf, but my dendrobium and oncidium arn't liking it so much, on my dendrobium it has three stalks, the biggest one is doing fine, it had a flower stalk on it, which I cut off recently but the two smaller ones are shrivling and the leaves are turning yellow, and just today I noticed that on my oncidium the newest shoot is turned yellow now (it's about eight or so inches long) I've got all of them sitting under a tree so they don't get to much direct sunlight, but they do get plenty of indirect, anyone got any ideas?

thanks!