hunchback, load
駝 centers on a curved, burdened back: a hunchback or a camel-like animal used for carrying loads. The two meanings connect through the image of a bent spine under weight.
駝 combines 馬 (horse) with 它, which likely contributes the sound and may suggest a bent or burdened shape. The character originally referred to a camel or pack animal, later extended to hunchback.
A horse (馬) with a curved back (它) carries a heavy load, like a camel or a person with a hunchback.
For ダ, imagine a hunchbacked camel carrying a load of dark (ダーク) goods: dark -> ダ, and the bent back supports the weight.
ostrich (Struthio camelus)
camel
rhea (bird of family Rheidae)
Arabian camel; dromedary; one-hump camel
two-humped camel; Bactrian camel
charcoal burned in an earthen kiln
inocelliid snakefly (any insect of family Inocelliidae)
tinamou (any bird of family Tinamidae)