Why are San Jose birds perching on power lines above Highway 85?

DEAR JOAN: We regularly notice a line of birds perched on the same wire no matter when we drive by. There is a set of two wires, and they’re always on the same one.

This is on Highway 85. We notice it going southbound, right before you get to the Winchester Boulevard exit and south of Saratoga Avenue.

You see this in other places, perhaps, but it’s puzzling over a busy freeway.

Any idea what this could be about?

Bonna Kauffman, Los Gatos

DEAR BONNA: I can’t speak for these birds in particular — maybe they’re all checking their Twitter accounts — but in general, birds have a thing for power lines.

Most of the birds you see perched on wires are passerines, which make up about half of all the birds in the world. They are built for perching, with one toe at the back of their foot and three in the front, allowing them to tightly grip a perch.

Originally, that was to hold onto tree branches, but as humans developed and created infrastructure, birds have take advantage of our unintentional generosity. Birds, of course, still perch in trees, but the overhead lines provide some advantages for them.

In the winter, the lines can be a toasty place to perch. We’re not talking steam heat here, but the lines are generally a few degrees warmer than other places, so that makes a nice place to sit.

The lines also provide a good place to gaze out on the openness in search of food. We often think this characteristic is more common in raptors, who spot prey from above, then swoop in, but other birds like having a high vantage point to scan the ground below for likely food spots — trees in bloom, plants going to seed, a swarm of insects and even a backyard feeder or two.

The lines also are a nice spot to rest, safe from dangers closer to the ground. Additionally, the lines can serve as a gathering spot to meet friends and family, and talk about events of the day. Migrating birds often will rendezvous on power lines, gathering numbers before heading off on their long journeys. Migrating in flocks makes flying easier as they draft off one another, and the group provides a measure of safety.

In particularly windy conditions, you’ll notice all the birds are facing the same direction: into the wind. That keeps their feathers from getting blown out of place. On windless days, the birds will sit any way they like.