As darkness arrived, I was unable to determine with any kind of certainty whether the Northern Mockingbird was pecking at Firefly. There were large numbers of Firefly rising, and one of the Northern Mockingbirds was rushing around, excited by something in the cut grass. And it's possible he was merely just showing off his gathering skills to an invisible other.
I have assumed that Mockingbirds do not see well in poor light. An assumption
based upon their stubbornness at roost. He'll sit in his tree and chortle an
advisory if you get close, but he'll not fly away unless he really has to. Then
if he does decide to fly in poor light, his flying is accompanied by a commotion
that I'll describe as 'embarrassing and very uncoordinated.'