The link to Shadrach’s article doesn’t work.None of my three do. I figure this is the reason.
https://www.backyardchickens.com/articles/the-egg-song-it's-not-about-the-egg-it's-an-escort-call
Very interesting article by Shadrach .
One night my husband heard a racket in the run. I ran down to investigate, and they were all "singing the song." And acting terrified, and looking at a spot in the nearby brush. I think it was a raccoon. The cockerel was very attentive too.
(@Shadrach).
And as @rosemarythyme says I also presume the chickens didn’t do the the egg-song but sounded the alarm-call.
Chickens make a lot of different sounds / sound combinations to communicate with each other.
I was once really flabbergasted when I took my Inimini home after she fled (flew over three hedges) from a dog and accidentally trapped in a neighbor's yard.
When I got her home after 24 hours, she started "talking" to her "sisters". All the chickens gathered around her and listened. The chickens all answer her in exactly the same way. A reassuring sound-combination. I assumed they told her it was okay now.