Peanuts by Charles Schulz for March 04, 1966
Transcript:
Snoopy lies on the doghouse with a birds nest resting on his stomach. He thinks, "How do things like this happen to me?"<BR><BR> Snoopy thinks, "I'm too easy going, that's why! I should have said something as soon as that stupid bird started to build this nest . . ."<BR><BR> Snoopy thinks, "The next thing you know there'll be . . ."<BR><BR> Two baby birds poke their heads up from the nest and Snoopy thinks, "I knew it!!"<BR><BR>
In at least one interview (I couldn’t give the exact source), Schulz said that this is the story arc where Woodstock first appeared, with him being one of the baby birds, continuing with one of them returning and continuing to hang around, until Snoopy came to regard him as his “friend of friends”, along the way working as Snoopy’s caretaker or secretary and finally being given a name around 1970.