The San Quintín Kangaroo Rat is Not Extinct

Abstract

The range of the San Quintín kangaroo rat (Dipodomys gravipes) is restricted, so far as known historically, to a stretch of coastal habitat less than 150 km in length and a few kilometers in width (Best and Lackey 1985) at the southern end of the California Floristic Province—a global biodiversity hotspot and one of the most critically endangered ecosystems on earth (Myers et al. 2000). This rodent was described in 1925 by Laurence M. Huey, who reported it from the coastal plains from San Telmo south to El Socorro and on the floodplain of the Arroyo El Rosario along the Pacific coast of northern Baja California, Mexico. The area between El Socorro and El Rosario is largely unsuitable. Huey asserted that the “mother lode of this species is found near Mesa Agua Chiquita, with 1,000 individuals in 10 acres” (field notes archived at the San Diego Natural History Museum). He described the habitat in this area as hard [clay] soils covered with grasses. Little is known about the broader habitat requirements for D. gravipes, but it appears similar in its niche requirements to Stephen’s Kangaroo rat D. stephensi which occupies areas with high disturbance, open conditions and weedy forbs (Tremor et al. 2017). Burrow entrances were closed but connected by visible runways up to 75 m long (Fig. 1). Previously, Nelson (1922) had written that in this area “the vegetation is so low and insignificant that the plain has the appearance of an open prairie”. Both descriptions could refer to areas recovering from wheat cultivation years earlier, and the grasses could be non-native annual species (e.g., Bromus spp.). Agriculture in the San Quintín area began in 1891 when British farmers converted parts of the landscape to wheat cultivation, built a dam for irrigation, and installed a flour mill (Taylor 1996). The settlement was abandoned in 1917 (Phelts-Ramos 2004). Subsequently, only four ranches persisted in the San Quintin Valley, until 1947, when Title 3050 (which granted agricultural lands to families from other regions of Mexico as a cession by the government) led to a massive expansion of agriculture in the valley (Ramírez-Velarde 2004). However, full expansion of agriculture in the area was restricted by the lack of roads allowing for export of produce from the area, until 1973 when the road connecting it with Ensenada was paved. In 1972, before the building of the transpeninsular highway, “the broad open areas 8.5 miles N of San Quintín were dotted with D. gravipes burrows” (Best 1983). Eight years later this area was converted to cropland. In 1980, the population had shrunk, and Best trapped only two individuals in >1000 trap nights. Likewise, the area 9.6 km east of El Rosario, where he had collected 35 specimens in 1972, was in 1980 covered by the paved transpeninsular highway (Best 1983). The Arroyo del Rosario area still produced 7 specimens in 1989 (Troy L. Best in litt. to EM, 20 July 1989).