Surprising that the Forum has so little on this familiar tune, which dates from at least 1757.

Here's a bit of folklore of the folk-etymology sort.

Macon [Mo.] Chronicle-Herald (Sept. 25, 1935):

"'The Camels is Comin' is one of the very old and very popular airs that have come down to us. It is supposed to have been inspired by the Arab camel drivers, and gives this call--'Heigh-ho!'"

Some may recall an ancient Bug Bunny cartoon in which a camel sings the (repeated) first line.