Where do the Bay Area’s birds go to sleep at night?

DEAn JOAN >> We have a lot of trees in our backyard and lots of birds feeding on sunflower pieces, and hummingbirds and orioles feeding on sugar water.

The seed-eaters are mostly goldfinches, house finches, woodpeckers, chickadees and an occasional nuthatch. As I look out the window at 8 p.m., I see no birds. They’ve gone to bed, I assume.

I’m wondering where they go at dusk. What are their bedrooms like?

DEAn NILE >> With a few notable exceptions — owls, for instance — almost all birds call it a day when the sun sets. They stop feeding and doing other daytime bird activities and head home to roost. Where home is depends on the bird and sometimes the season. The primary concern is safety.

Water birds — ducks and geese — retreat to ponds, lakes and other waterways, standing in or floating on the water, safe from predators. If something tried to get to them, the birds would quickly be alerted by sounds or even ripples in the water.

Ground-nesting birds seek out hiding places on the ground, retiring to thick shrubs and piles of brush, but sometimes they prefer the safety of the trees. Birds that normally nest in trees return to the branches, and sometimes to their nests, but any high, protected limb can serve as a sleeping spot.

Cavity-nesting birds, such as woodpeckers or Western bluebirds, may retire to their hollowed out trees or nesting boxes, or sleep in the open on tree branches. Woodpeckers often create a separate hollow, away from their nesting holes, to sleep.

When it’s not mating season, many birds choose to roost together in trees, relying on the safety of numbers not only for protection, but for warmth.

DEAn JOAN >> I have had a single hummer feeder for over 10 years. These little guys and gals bring me joy every day.

When the feeder is near empty, I wash it with soap and water, then swish around some bleach, rinse thoroughly, and finally run through the dishwasher.

In the last few months, after a few days hanging, I have noticed a thin “something” floating around in the clear glass — kinda like cotton candy. Could this be some sugar dropping out of suspension — I use a 4-to-1 water-sugar ratio — or might I have a bacterial infection?

DEAn BOB >> Filmy substances floating in nectar are usually a sign that mold is beginning to grow. The hummingbird feeder should be emptied, cleaned and refilled the minute you see it.

If you’re worrying that you are doing something wrong, don’t. This happens when it’s very hot outside. The nature of the sugar water tends to produce mold in the heat. You can decrease the likelihood of nectar spoiling, however, by putting the feeder in a shady area.

Nectar can appear cloudy or have bubbles for other reasons, including the sugar falling out of suspension. Make sure the water is hot enough to dissolve it. Sometimes it can appear cloudy before you even hang the feeder. That’s likely caused by air in the mixture. Let it sit on the counter for about 15 minutes before putting it out.