The phenomenon of North American birds being killed by becoming entangled in Common Burdock (Arctium minus) has been documented since at least 1909, when one observer (in A.C. Bent’s compilation) described finding a multitude of Golden-crowned Kinglets in Common Burdock’s grasp:
They were visible in all directions, scores of them sticking to the tops of the clumps on the most exposed clusters of heads. The struggle had ended fatally for all that I saw, and its severity was evidenced by the attitudes of their bodies and the disheveled condition of their plumage. I examined a number of the burdock heads to determine that attraction had brought the kinglets within range of the hooks, and found insect larvae of two species present in considerable abundance.
Typically this phenomenon involves birds that are seeking either insects that are inhabiting the seed heads, or burdock seeds. The birds’ feathers get caught by the hooked bracts (modified leaves) that surround both the flower heads and seed heads of burdock. Small birds such as kinglets, gnatcatchers, goldfinches, nuthatches, hummingbirds, chickadees, warblers and siskins are the usual victims, but larger birds, including a Blue-headed Vireo and a Barn Swallow, have been caught as well. Most of these birds were found with their wings and tail spread, and caught by many parts of their bodies. The more they struggled, the more their feathers became entangled. Victims are not limited to birds — in 1925, a dead bat was discovered caught in a patch of burdock. (Photo by and thanks to Holly Brough)