If you post a picture on Name That Plant Forum you could get an id and know if it's edible.

Could it be your climate? I have the opposite problem in zone 9. My chard grows so big and fast I can't keep up with it and it becomes a hiding place for snails. Is your raised bed on top of soil or something else? Here is a link that might be useful: My raised bed garden

This doesn't shock me after something I witnessed last year. We seemed to catch the "great goldfinch migration" with literally 40 to 50 finches in our yard during a 1 day period (our normal summer finch activity is 4 to 5 mating pairs of goldfinches and a few house finches). The goldfinches certainly swarmed the finch feeder, but the really weird behavior was how they all lined up at the border between the street and our yard in order to eat dandelion greens. To this day, I hay no idea why they were eating dandelion greens, but there is no question that is what most of the "flock" was doing. But eating chard leaves wouldn't surpise me.

Oh, I have a GREAT recipe for you! I grew Swiss chard this year, so I had my own to use for this. I'm hoping that enough will grow back before the frost kills it to make it once more. I think you can use most greens pretty much interchangeably. I even discovered that the enormous greens from my horseradish plant are delicious, especially with white beans and sausages. Mmmm! I love this dish. I made it for Rosh HaShana this year. It's an Iraqi Jewish recipe, and it was in the New York Times food section before RH a few years ago. When our picky picky foodie friends came from Israel for my son's wedding, there was a tiny dab of leftover in the fridge, and they ate it for a snack and decided I was a great cook after all. :-) False Mahshi: Layered Swiss Chard, Beets, Rice and Beef NYT September 23, 2008 Adapted from Esperanza Basson Time: 1 hour, plus 1 hour for soaking rice 1 1/2 cups long-grain jasmine rice 2 pounds rib-eye steak, cut in 1-inch cubes (I used a cheaper cut -- maybe shoulder steak? -- and it was fine.) Salt and coarsely ground black pepper 6 tablespoons vegetable oil 2 large onions, peeled and diced 2 large beets (about 1 pound), peeled, 1 cut into 1/2-inch dice and 1 grated (I like more) 1 pound Swiss chard, leaves left whole and stems cut into 2-inch pieces 8 teaspoons sugar, or as needed 4 tablespoons fresh spearmint leaves 1 teaspoon dried mint 4 cloves garlic, peeled and finely diced Juice of 3 lemons (about 1/2 cup), or as needed. 1. Place rice in a mixing bowl and cover with water. Stir, drain off cloudy water, and repeat until water runs clear. Cover rice with fresh water and let soak for about 1 hour. 2. Season beef with salt and pepper to taste. Place Dutch oven over medium heat and add 1 tablespoon of oil. When oil is shimmering, add beef and saute until well-browned on all sides, about 5 minutes. Remove beef and set aside. Return pan to low heat and add 2 more tablespoons of oil. Add onions and saute until transparent, about 5 minutes. Add diced beets and saute for another 5 minutes. Add two-thirds of the Swiss chard stems and continue cooking until onions are golden, about 5 more minutes. Stir in beef, cover, and remove from heat. 3. Drain rice and return to a bowl. Sprinkle with salt to taste, 5 teaspoons of sugar, 1/2 teaspoon black pepper, 1 tablespoon fresh mint and dried mint. Stir to blend, and add garlic, grated beet, remaining oil and juice of 1 lemon. Spread one-third of Swiss chard leaves in Dutch oven, on top of beef mixture. Spoon half of rice mixture on top, and cover with another third of chard leaves. Spread with remaining rice, and top with remaining Swiss chard leaves and stems. 4. In a small bowl, mix 1 1/2 cups water with remaining 3 teaspoons sugar and juice of another lemon. Taste and, if necessary, add more sugar or lemon juice so mixture is both sweet and sour. Pour over Swiss chard and bring to a boil. Cook partially covered until chard begins to wilt, 3 to 5 minutes. Add 1/2 cup water if pan is very wide and there is little liquid on bottom. Poke handle of a wooden spoon into mixture in three places, making holes to let steam rise through chard. Cover, reduce heat to very low, and cook until rice is tender, about 30 minutes. Remove from heat and let rest for 15 minutes. Just before serving, sprinkle with remaining lemon juice and remaining fresh mint. Yield: 6 to 8 servings. (I think it makes a lot more.)