As far as I can read, the oldest lore on Kenku states that they are avian humanoids who lost their wings and speech when they defied their god. However, I can't help draw striking, yet vague links between their description and that of the Aarakocra leaving me to assume they were once the same race.
While I have neither found sources to confirm or deny this, I did find that the issue might be stemmed in that the Kenkus predate 5e, so I thought I'd ask here, as it has helped me in a similar situation before:
Are Aarakocra and Kenku related? Were Kenku once Aarakocra who had fallen from grace, or were they another race of avians all together? And if so, what kind of race were they before they lost their wings?
Best Answer
No
It's nigh impossible to prove a negative for "designer intent", but at least as far back as AD&D 1E, there's no published indication that they're related.
The biggest giveaway that any relationship would be distant/non-existent is their morphology in their early appearances. While both of them have six "limbs" in 5E (at least according to the aarakocra illustration on D&D Beyond), two legs, two arms, and two wings, in both 1E & 2E only kenku had that design, while aarakocra had hands on their wings, without a separate set of arms (only four "limbs"). Other differences include:
It's possible later writers thought of them similarly and their descriptions drifted closer, but originally, they were very different, aside from the surface similarity of both being "bird-men".