I bet there are probably lots of bugs on those trees. I've noticed that the cardinals like hanging out in the spruce trees as it has a nice dense canopy for them to hide in. Could be spiders there as that is part of their diet.

My hummers are always at the spruce and fir trees. They especially like the Dwarf Alberta Spruces. The small needles of this plant are home to many tiny spider webs. In the spring the hummingbirds seemed to favor these evergreens over the feeder and nectar plants. Most likely they were collecting small spiders and insects for their chicks.