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! :)