The red knot is a sandpiper that nests in the Arctic but spends winters on the Atlantic Seaboard. It is one of 233 species on a watch list of threatened species. (Gerrit Vyn)

From my humble plastic chair at the community garden, I can look up to my neighbor’s fence, which is heavy with the violet flowers and red-purple pods of the hyacinth bean, and wait for a little visitor.

She arrives as a flash of electric green, a hummingbird whose long bill probes deep into the pealike blossom for its reward of sweet nectar. Sometimes, she dispenses with the aeronautics and simply perches on a stalk. She negotiates her beak a little awkwardly, and sups on her feet. I find this touching, in a strange way, and a privilege to witness.

Hummingbirds come and go with their endless quest for energy, but they vanish too with the seasons. Soon, they will be flying south for the winter, along with the warblers and the catbirds, and their departure is part of the sadness the gardener feels when the growing season comes to an end.

Avoid the temptation to keep the hummingbird feeder stocked with sugar water — this can cause them to linger longer than is good for them, says Pete Marra, director of the Smithsonian’s Migratory Bird Center. He has been thinking a lot lately about the welfare of all the bird species in North America. He and other experts from government and conservation agencies have issued a State of the Birds Report that examines bird population trends in seven habitat types. The survey has a special poignancy this month, which marks the centenary of the extinction of the passenger pigeon, a bird once so numerous that flocks would darken the sky for days on end. Habitat destruction and relentless hunting doomed the bird.

The results of the report are mixed; some habitats are seeing alarming drops in bird numbers, others are remaining level or improving. And within habitats, some species are faring better than others. Eastern meadowlarks are disappearing but other grassland species are holding their own. Most freshwater birds that live in wetlands have rebounded, due in large part to the North American Wetlands Conservation Act.

The cerulean warbler is an uncommon wood warbler that breeds in Eastern forests but spends the winters in the tropics. It has benefited from habitat conservation. (Gerrit Vyn)

The biggest single threat to birds remains the loss of the environments they need to flourish and reproduce, but habitats can be restored by protecting public land and adopting policies that encourage private conservation and ecologically sensitive farming.

The steepest drop was in Western aridlands — desert, sagebrush and chaparral — where bird populations have declined by almost half since 1968.

Birds that visit the Mid-Atlantic as migrants, including my little hummingbird, live their winter lives not only in different climates and regions, but also in different countries. This makes protecting their habitats more difficult, but not impossible.

The cerulean warbler is a rare wood warbler that breeds in Eastern forests but winters in the tropics. It has benefited from conservation efforts in the United States and also in the coffee-growing regions of Colombia.

The warbler is one of 233 species that the report’s authors — the U.S. Committee of the North American Bird Conservation Initiative — have placed on a watch list of birds that are endangered or will be without significant conservation efforts.

Separately, the National Audubon Society this month released a study of the future effects of climate change on birds and predicted that 314 species could lose most of their current habitats by 2080 because of global warming.

While that study looks forward, the State of the Birds Report looks back. More than half of our shorebird species are on this list, including a handsome sandpiper named the red knot, which winters on the Atlantic Seaboard. “Its populations have declined by 95 percent since 1968,” Marra said.

Most people have little direct control over some of the factors that have harmed birds — the effects of overfishing on ocean birds, for example — but many of us with a little patch of land have a chance to give birds a helping hand. Washington’s urban forest is a vital asset. Marra said the mature tree canopy of Takoma Park, where he lives, has done much to harbor such beloved bird species as the Baltimore oriole, great crested flycatcher and eastern wood-pewee.

Although the major habitat gains are made in the preservation of large areas of land, “there are lots of ways that individuals can help these birds,” said Ken Rosenberg, a conservation scientist at the Cornell Lab of Ornithology.

What can we do in the residential landscape? First, keep cats indoors. Cats kill an astonishing number of birds in this country, as many as 2.4 billion a year. The mere presence of a cat can affect the breeding success of a nesting bird. “A parent bird reduces the rate at which it feeds nestlings when it glimpses a cat,” writes John Marzluff in a new book, “Welcome to Subirdia,” in which he argues that suburban landscapes can offer vital habitat for beleaguered bird species.

We can choose to grow plants that foster abundant insect life (oak trees are much commended), or provide winter berries, or simply offer cover from predators and a place to roost. Bird feeders help (keep them away from windows to avoid collisions). Fresh water acts as a magnet for birds. If you have birdbaths, change the water regularly in summer to thwart mosquitoes, and in winter to replace ice. Water to drink and for bathing seems even more attractive than bird seed.

“I can’t believe how many birds come to my pond, said Marra. “During migration, birds are dehydrated.”

And the idea that the hummingbird or the oriole nests in our gardens for just a few weeks and then travels many hundreds of miles to its other existence is sort of magical. As Marra puts it: “Our back yards are connected to a whole other world.”

That idea alone should be enough to make us want to nurture our feathered friends. If they seem fragile, perhaps it’s because they are. As the loss of the passenger pigeon has taught us, surely the worst thing we could do for our birds would be to take them for granted.

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