Alien Plants

Common Burdock - a Kinglet Killer

Jean Iron

On October 9, 2001 while birding in Brookbanks Ravine near my house in Toronto, another walker told me about the little birds that were "trapped in thistles." Intrigued, I went to the spot and saw two dead kinglets hanging in the burs of Common Burdock (Arctium minus), one a Golden-crowned Kinglet and the other a Ruby-crowned Kinglet.

On October 17, I again checked the Common Burdock plants in Brookbanks Ravine for trapped birds. Along a 200 meter stretch I found 8 dead kinglets in the burdock burs, most were Golden-crowned. The birds were spread-winged, spread-tailed, and caught by many parts of their bodies, including the bill. The more they struggled, the more they became stuck. I estimated they had died over a period of a few days to several weeks earlier.

While doing the Hamilton Naturalists' Club Fall Bird Count in Centennial Park near Van Wagners Beach on November 2, I found a dead Golden-crowned Kinglet trapped in a patch of burdock.

Again in Brookbanks Ravine on November 19, I found a freshly dead Golden-crowned Kinglet trapped by the burs of burdock.

Common Burdock is a plant with large flat leaves that look like rhubarb. The flowers resemble thistles and when they die the seeds forma  round ball that attaches by its barbed velcro-like hooks to clothing, dogs, anything it touches. Common Burdock grows 1 - 1.5 meters tall or more. Each stalk is loaded with round balls of seeds surrounded by hooks. After a walk through a waste or brushy place, the odds are that you have had these burs clinging to your clothing. Burdock is not a native North American plant, but was introduced from Europe.

I wondered why there were so many dead kinglets in this stretch of Brookbanks Ravine. The burdock plants were close to the creek and the edge of the woods. They were growing close to goldenrod, asters, wild grape and other fruit and seed-bearing plants.

When the kinglets migrated through in September and October, they probably gleaned insects from the flowers and seed heads of goldenrod and other plants and inadvertently became trapped in the burdock. Because of their small size, many kinglets were unable to escape and became more stuck as they struggled. On October 19, I noticed House Sparrows going in and out of the burdock, but did not find any of this species entangled.

Mark Kubitz (1989) reported finding a Golden-crowned Kinglet trapped in burdock in May 1989. A spring occurrence is unusual as most birds are trapped in the fall. He located literature reports that involved the following birds killed by burdock: Blue-headed Vireo, American Goldfinch, Ruby-throated Hummingbird, Yellow-rumped Warbler, Common Yellowthroat, Pine Siskin and Black-capped Chickadee.

Brewer (1994) reported finding a dead Blue-gray Gnatcatcher caught in burdock. Martin McNicoll (1994) updated the literature review and reported the following being hooked: Magnolia Warbler, Red-breasted Nuthatch, and a warbler. Even small bats have been killed in this way.

In Bent (1949), James G. Needham in 1909 describes finding "scores" of Golden-crowned Kinglets entangled in the hooks of the ripening heads of burdocks one autumn in a partly wooded pasture near Lake Forest, Illinois (USA).

Needham wrote, "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. Most abundant were the seed-eating larvae of an obscure little moth (Metzgeria tapella), but the larvae of the well-known burdock weevil were also present in some numbers. Doubtless, it was in attempting to get these larvae that the kinglets (mostly young birds) were captured."

Small birds like kinglets stand no chance against burdock, whose seed heads are a mass of barbed hooks. I got a barbed seed stem in my eye and had to go to an eye specialist to have it removed.

This summer I will be cutting the large basal leaves of burdock plants before they flower and set burs. I urge others to remove this deadly [and invasive alien] plant in your area to save the lives of many small birds.

Acknowledgements: I thank Ron Pittaway for valuable comments and discussions on burdock and birds, and Ron Tozer for checking references.

References:

• Brewer, D. 1994. Ontario Birds 12(3):115-116.

• Kubitz, M. 1989. Ontario Birds 7(3):112-114.

• McNicoll, M. 1994. Ontario Birds 12(3):117-119.

Reprinted from OFO NEWS: Newsletter of the Ontario Field Ornithologists, Volume 20, No. 2, June 2002 (and subsequently the Wood Duck (Hamilton Naturalists Club newsletter, September 2002).