Link to the paper, and excerpt from the conclusion:

In our study, we showed that baby domestic chickens (Gallus gallus) respond to sound-symbolic associations similar to humans, preferentially matching the sounds ‘Bouba’ and ‘Kiki’ to a round and a spiky shape, respectively.

This could be convergent development between mammals and aves, but honestly I think it’s inherited. (I wonder if lizards show evidence of the effect? Some can be quite smart, like green iguanas.)

If inherited then we’ve been subjected to the bouba-kiki effect for more than 300M years — kind of funny how something so old would have an impact on Language later on, for some weird clade of hairless apes.