I remember I have stumbled upon 3 super similar suggested themes for LD53 and it was Birds.

I compiled bird games that I have found so far to this list so you can try them out:

https://ldjam.com/events/ludum-dare/53/special-delivery-3

https://ldjam.com/events/ludum-dare/53/feed-the-owlets

https://ldjam.com/events/ludum-dare/53/express-stork-delivery

https://ldjam.com/events/ludum-dare/53/animaternity

https://ldjam.com/events/ludum-dare/53/stork-inc-1

https://ldjam.com/events/ludum-dare/53/out-of-pigeons

https://ldjam.com/events/ludum-dare/53/cigognes-baby-delivery-services

https://ldjam.com/events/ludum-dare/53/the-pigeon-post-principle

And lastly, our teams implementation of themes was a 3D "baby delivery" on a fertility island: https://ldjam.com/events/ludum-dare/53/fertility-island

Feel free to add more in the comments. Lets play those bird games! :)