Dispersal of Leafy Spurge (Euphorbia esula L.) Seeds in the Feces of Wildlife

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Leafy spurge (Euphorbia esula) is an exotic, perennial, invasive weed in many areas of the northern United States and Canada. There are many instances in pastures and wildlands where individual or small clusters of leafy spurge plants are distant and upslope from larger patches, and wildlife have been suspected as seed dispersal agents. Wildlife can disperse seeds by ingestion then excretion of seeds in their feces. Fecal deposits of free-ranging deer (Odocoileus hemionus and O. virginianus; n = 176), sharp-tailed grouse (Tympanuchus phasianellus; n = 201) and wild turkeys (Meleagris gallopavo; n = 206) were collected during a summer in Theodore Roosevelt National Park (TRNP) in western North Dakota, and for deer only in Medicine Lake National Wildlife Refuge (MLNWR) in northeastern Montana. Feces were analyzed for the presence of leafy spurge seeds and any seeds found were tested for germinability and viability. Only one intact leafy spurge seed was found in one grouse fecal deposit and it was not viable. No leafy spurge seed was found in turkey feces. Two seeds that appeared to be immature leafy spurge seeds were found in one deer fecal deposit in TRNP, but neither seed was viable. One leafy spurge seed was found in each of four deer fecal deposits from MLNWR, but only one seed was viable and germinated. Seed-feeding trials with captive deer (n = 4), sharp-tailed grouse (n = 4) and wild turkeys (n = 4) were conducted to determine how leafy spurge seeds interact with the digestive systems of these animals. The only viable seeds defecated by grouse and turkeys were seeds excreted one day after ingestion. Two turkeys did not excrete any leafy spurge seeds and only a few viable seeds were defecated by the other two. One grouse defecated a larger number of viable seeds, but the other three grouse excreted only a few. Deer defecated viable seeds each of 4 d after ingesting them with most viable seed excreted on the first 2 d. These findings, along with those for the free-ranging animals, indicate that wild turkeys probably do not disperse leafy spurge seed while sharp-tailed grouse and deer may do so on a limited basis.