A great blue heron is a breathtakingly elegant bird with a goofy soul. This reporter once watched one stalk, quiet and purposeful, along the edge of a pond, spear a fish lightning-fast — and then flap around in a panic, trying to get the wriggling creature off its face. In a hidden back garden in Burlington's South End, artist Melanie Brotz has captured the bird's poise and prowess, as well as its occasional awkwardness, with a series of more than 20 driftwood herons, cranes and storks. Spanning roughly three to more than 10 feet high, they camouflage amid the garden's late-season foliage. On a recent weekend, Brotz hosted a garden party exhibition at which 50 to 60 friends and neighbors met the creatures. Brotz has been collecting driftwood for decades. On a garden tour, she said, "I've always wanted to build with it, and I always thought, I don't know enough about woodworking." Then, a couple of years ago, during a weeklong art residency at Rock Point in Burlington, she thought, "What's the worst that can happen — I break a piece of driftwood?" Since the initial sculpture she made on the beach, which incorporates a smashed fragment of a varnished wooden boat, Brotz has made many more, always searching for roots and branches that conjure feathers, legs and heads. Most of her materials come from Lake Champlain or the Winooski River — especially the corners where flood detritus has piled up in recent months. That's not all Brotz and her husband have found, she said: "We were on the Winooski River trying to look for driftwood, and, unfortunately, what we kept finding was foam: garbage, garbage, garbage foam." Chunks of that material — the foil-backed or blue rigid insulation used in many homes — comprise a few other sculptures Brotz has made. She skewered the foam as a way to carry it out of the river, and the resulting piles resemble rock cairns. They're deceptively peaceful and natural-looking. Brotz also makes stained glass and paintings — some are of the same birds she sculpts — and other projects. She cofounded Burlington's South End Art Hop, which just celebrated its 32nd year and now boasts days of programming, hundreds of artists and more than 35,000 visitors. Five years ago, Brotz spurred a local mystery with her "Signs of Love" project, placing tiny, affirming placards in unobtrusive locations…