If you've ever watched a chicken hunt mice, you know what mammals went through the last 200 million years.
This was a local wild chicken that had presumably escaped from a coop, and it appeared to sustain itself on mice all summer.
And you can't help but feel a pang of regret for the vermin. You lost many of your ancestors in just this way. You're a survivor. Tomorrow you're going to eat that egg. In revenge.