|Sunflowers in decline|
Sunflowers are an ideal food source for birds through the decline of the season. Migratory birds feed on insects and seeds during the summer and head south before the weather turns severe, but a number of birds don't migrate and need energy to survive the winter. You've seen them on cold days, perched on power lines or a high branch. They're usually dark colored; shadows sitting against the gray sky. These are the birds that will benefit from the sunflowers you leave standing.
Sunflower seeds, particularly the black oil sunflower seed, are a prevalent component of many commercial seed mixes. They supply nutrition and energy to many different birds. Some commercial mixes may grind or break the seeds to allow access to smaller birds that wouldn't normally be able to break open the shell. Placing seeds in a feeder or dish is a great way to supplement your local bird population when the insects are gone and flowers are in short supply.
Leaving free-standing sunflower plants in your garden will do this naturally. Medium-size birds will land on big heads and pluck out some seeds. I saw a small flock of red-winged blackbirds attack my sunflowers a week ago. They are not precise feeders; as they peck and pull, a multitude of seeds will fall to the ground. Larger birds that are too big to perch on a precarious flower can forage the fallen seeds. Our blue jays and magpies are often seen at the base of the stalks. The big birds will crack the seeds and pieces of the kernel will fall out. Small birds will later feed on these bits. Chickadees will gather, pecking, in the shade of the dead plants.
With a large crop of sunflowers, this pattern will continue for months. At intervals, birds will arrive, feed, and fly away. The sunflower patch is nature's equivalent of a food court in the mall. If you plant a variety of sunflowers you'll see a variety of birds. Smaller flowers will be visited by smaller birds, but the feeding process will be the same.
By winter's end, most or all of the seeds will be gone. There will still be time to prepare the site for the next season's plantings. Don't be surprised if some of the discarded seeds sprout in the spring. It's possible for these annual flowers to become established year after year by the natural sowing by the birds. If you don't have sunflowers and the idea is intriguing, pick a location that can become their permanent home. If you have sunflowers and haven't cut them down, leave them be and let the birds feed. You'll be making a small contribution toward establishing a natural habitat.