Why are birds eating this plant?

Hi all.

I’ve noticed that a Dunnock was recently pecking repeatedly at the leaves on my mom’s little potted Sea Campion plant, and then a Wren was having a good go at it the following day. Not sure why they are doing this. Never seen them peck at little potted plants before. Is there something about Sea Campion that they like?

Here’s a picture of the state of the little plant after all the pecking. The brown shrivelled bits must be what they have created!

 https://imgur.com/a/NQwnIp4

Really intrigued!