Something (bird?) puked on my planter, why do the seeds germinate early around it?

I don't have any pets and I live on the fifth floor of an apartment so I guess birds are messing with my planters.

Two days ago I noticed there's a vomit (I think?) or something like that on my coriander planter but I forgot to clean it up. Today I found that some of the seeds have germinated but it's localized around the puke (lol). I cleaned it up but I wonder why it does that.

Should I be worried about birds ruining my seedlings? I mostly only plant herbs and vegetables. I'm not too sure about putting netting because I don't get a lot of sunlight on my balcony (facing NE).