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The Virginia opossum (Didelphis virginiana) is native to much of the North American continent, ranging from extreme southeastern Canada through the eastern United States and most of mainland Mexico to Costa Rica (Hall, 1981). Multiple introductions in western North America, primarily along the Pacific coast, began in California around 1900, as mapped and described in considerable detail by Grinnell et al. (1937). The species is now widespread from southwestern British Colombia to the Mexican border, with outlying populations in the interior (Banfield, 1974; Hall, 1981).

At the south end of the Pacific range, in San Diego County, Bryant first reported the opossum in 1926 (Bryant, 1927). Without acknowledging the international border dividing it, Huey (1964:91) reported that opossums were "common residents along the Tijuana River bottom." More specifically, he reported the existence of a caged opossum that had been captured by local residents 10 km east of Tijuana in May 1962, but no specimen was retained and no other Baja California specimens are known to exist (S. Tremor, pers. comm.). Despite these early findings, one individual captured and released in Ensenada in November 1997 (Mellink, 1998) has been the only subsequent published report from Baja California (Gardner and Cortes-Calva, 1999; Zarza and Medellin, 2005, 2014).

Erickson found road-killed opossums on Mexico Federal Highway ID at Real del Mar (32[degrees]26,38,,N, 117[degrees]06,08,,W; just south of Tijuana) on 23 March 2004 and at La Fonda (32o07,16"N, 116[degrees]53,03,,W; approximately half way between Tijuana and Ensenada) on 3 April 2018 (Fig. 1), but saved no specimens. Based upon conversations with long-time residents of the La Mision area (extending roughly from La Fonda through Playa La Mision and Colonia Santa Anita to Ejido La Mision), opossums have been present in the developed area between Colonia Santa Anita and Playa La Mision since approximately 2015. Residents often see them feeding on pet food left exposed. Local resident Erin Dunigan, aware of our interest in the species, salvaged three opossums killed by dogs in this area (32[degrees]05,48,,N, 116[degrees]52,30,,W) between 23 May 2018 and 24 April 2019. Ruiz-Campos prepared the specimens for skin and skull and deposited them in the Mammals collection of the Universidad Autonoma de Baja California (UABC) at Ensenada (Fig. 2):

Juvenile (UABC-1206, 277 mm and 97.3 g total length and weight, respectively) collected 23 May 2018;

Male (UABC-1172, 375 mm and 302.4 g) collected 23 April 2019;

Female (UABC-1171, 416 mm and 333.8 g) collected 24 April 2019.

Opossums within California have behaved largely as human commensals. Marcum (2017:18) considered the species "common in urban and agricultural areas at low elevations" on the west side of San Diego County. The arid and largely undeveloped landscape between Tijuana and Ensenada was historically inhospitable for the species, but things have changed with increasing development along this coveted stretch of shoreline. Other recent examples of species, native and nonnative, that have capitalized on this situation and extended their ranges from coastal southern California south toward the Ensenada area and beyond include the giant swallowtail (.Papilio cresphontes; Erickson and Iliff, 2004), scaly-breasted munia (Lonchura punctulata; Erickson et al., 2013), African clawed frog (Xenopus laevis; Peralta-Garcia et al., 2014), and sedentary Allen's hummingbird (Selasphorus sasin sedentarius; Erickson, 2016). We expect many more species to follow.

Residents of the La Mision area, essential in the preparation of this note, include N. de Jong, E. Dunigan, J. Garcia Arellano, J. and S. Stadelman, and J. Thomas. Others who assisted in rounding out our research include M. J. Billings, L. Erickson, E. Mellink, S. Tremor, J. Vargas, and E. D. Zamora-Hernandez.



BANFIELD, A. W. 1974. The mammals of Canada. University of Toronto Press, Toronto, Canada.

BRYANT, H. C. 1927. The opossum reaches San Diego County. California Fish and Game 13:146.

ERICKSON, R. A. 2016. Allen's hummingbird nests in Mexico: expansion of Selasphorus sasin sedentarius into Baja California. Western Birds 47:161-166. doi:10.21199/WB47.2.5

ERICKSON, R. A., AND M. J. ILIFF. 2004. Occurrence of the giant swallowtail (Papilo cresphontes) in northern Baja California. Southwestern Naturalist 49:506-508.

ERICKSON, R. A., R. CARMONA, G. RUIZ-CAMPOS, M. J. ILIFF, AND M. J. BILLINGS. 2013. Annotated checklist of the birds of Baja California and Baja California Sur, Second edition. North American Birds 66:582-613.

GARDNER, A. L., AND P. CORTES-CALVA. 1999. Family Didelphidae. Pages 29-37 in Mamiferos del noroeste de Mexico (S. T. Alvarez-Castaneda and J. L. Patton, editors). Centro de Investigaciones Biologicas del Noroeste, S. C., La Paz, Baja California Sur.

GRINNELL, J., J. S. DIXON, AND J. M. LINSDALE. 1937. Fur-bearing mammals of California. University of California Press, Berkeley.

HALL, E. R. 1981. The mammals of North America. John Wiley and Sons, New York.

HUEY, L. M. 1964. The mammals of Baja California, Mexico. Transactions of the San Diego Society of Natural History 13:85-168.

MARCUM, S. 2017. Virginia opossum, Didelphis virginiana. Pages 17-20 in San Diego County mammal atlas (S. Tremor, D. Stokes, W. Spencer, J. Diffendorfer, H. Thomas, S. Chivers, and P. Unitt, editors). Proceedings of the San Diego Society of Natural History 46.

MELLINK, E. 1998. Ampliacion de la distribucion del tlacuache (.Didelphis virginiana) en Baja California. Revista Mexicana de Mastozoologia 3:148.

PERALTA-GARCIA, A., J. H. Valdez-Villavicencio, and P. GalinaTessaro. 2014. African clawed frog (Xenopus laevis) in Baja California: a confirmed population and possible ongoing invasion in Mexican watersheds. Southwestern Naturalist 59:431-434.

ZARZA, H., AND R. A. MEDELLIN. 2005. Didelphis virginiana. Pages 108-110 in Los Mamiferos Silvestres de Mexico (G. Ceballos and G. Oliva, editors). Comision Nacional para el Conocimiento y Uso de la Biodiversidad: Fondo de Cultura Economica, Mexico City, Mexico.

ZARZA, H., AND R. A. MEDELLIN. 2014. Didelphis virginiana. Pages 76-78 in Mammals of Mexico (G. Ceballos, editor). Johns Hopkins University Press, Baltimore, Maryland.

Submitted 10 July 2018. Accepted 13 January 2020.

Associate Editor was Ray Ellis.


San Diego Natural History Museum,, P.O. Box 121390, San Diego, CA 92112 (RAE) Facultad de Ciencias, Universidad Autonoma de Baja California, Km. 103 Carretera Tijuana-Ensenada, Ensenada, Baja California 22800, Mexico (GRC) U.S. mailing address for GRC: PMB 064, P.O. Box 189003, Coronado, CA 92178

* Correspondent: richard.erickson@lsa. net

Caption: FIG. 1--Adult Virginia opossum (Didelphis virginiana) found dead on the highway at La Fonda, Brya California, 3 April 2018. Photo by Richard A. Erickson. (Color version is available online.)

Caption: FIG, 2--Three Virginia opossums (Didelphis virginiana) salvaged near Colonia Santa Anita, Brya California between May 2018 and April 2019. Photo by Gorgonio Ruiz-Campos. (Color version is available online.)
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Author:Erickson, Richard A.; Ruiz-Campos, Gorgonio
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1MEX
Date:Jun 1, 2019

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