We identified helminth parasites infecting the San Miguel Island fox, assessed the prevalence of these infections, and compared the observed helminth diversity with reports on other California Channel Islands fox subspecies and the gray fox, Urocyon cinereoargenteus. Samples were collected between February 2019 and January 2021. We reported seven helminth species to various degrees of prevalence and egg density per gram fox scat processed: Pachysentis canicola, Angiocaulus gubernaculatus, Uncinaria stenocephala, Spirocerca lupi, Calodium hepaticum,Toxocara canis, and Mesocestoides corti.

We collected 405 fresh scat samples along trails on SMI. From February 2019 to January 2021, ten scats were collected monthly around the SMI ranger station (NPS staff added considerably to these collections) for the purpose of understanding seasonality. In addition to these 239 samples, 166 scat were collected from 24 September to 24 October 2020 for an island-wide spatial study. All scats were homogenized upon collection and stored at -20°C until processed.

We used the standing fecal sedimentation and fecal flotation methods to search for helminth diagnostic stages (eggs and larvae) from each homogenized scat. Sediments and floats were examined under light microscopy (100-400x total magnification). For each sample, we recorded the date collected, date processed, total sample mass, subsample mass, subsample volume, volume searched, and the number and identity of all helminth eggs and larvae.