For four years, a mallard has nested behind a bush near the front door of Caitlin Deal's home in a Minneapolis-St. Paul suburb, offering an up-close glimpse of nature for her young son and lessons for how people can coexist with wildlife. The duck, dubbed Martha by the family, sits on her nest for about a month every spring in the tree-lined neighborhood of Eagan, Minnesota. After her eggs hatch around Mother's Day, the birds toddle away. “It feels nice that she trusts that area, that she us...