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Rosy Boa (Lichanura trivirgata)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2093″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Photo by Larry Jones[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2261″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Rosy Boa (Lichanura trivirgata), Sonora, MX. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][gap size=”30px” id=”” class=”” style=””][vc_column_text]

Description

The Rosy Boa (Lichanura trivirgata) is of moderate size (probably < 760 mm total length in our area) and characterized by numerous small scales on top of and on the sides of the head, the ventral scales are distinctly narrower than the width of the body, anal spurs – remnants of hind limbs – are located on either side of the vent and are especially prominent in males, the anal plate and subcaudals are undivided, three loreal scales are usually present on each side, and there are no chinshields. The eyes are relatively small and the pupils are vertically elliptical. The body is cream or tan with one broad, dark brown mid-dorsal stripe, and a broad dark brown stripe on each side. The ventral surface is pale with dark speckling.

This is one of four species in the tropical family Boidae to occur naturally north of Mexico, the others being the Northern Rubber Boa (Charina bottae) of extreme southwestern Canada and the western U.S., the Southern Rubber Boa (Charina umbratica) of southern California, and the Northern Three-lined Boa (Lichanura orcutti) of southern California, northwestern Baja California, and western Arizona. The latter species was only recently recognized. Wood et al. (2008) analyzed the molecular genetics of what was considered at the time to be one, broad-ranging species (L. trivirgata) and found that snakes with pinkish-orange stripes (now L. orcutti) were distinct from those with dark brown stripes (L. trivirgata – south of the Gila River in central Arizona and south to southwestern Sonora, and from the Tijuana and Otay watersheds of extreme southern California south through the Baja California Peninsula).  Specifically, in Arizona, the Rosy Boa occurs from the North Maricopa and Sand Tank Mountains southward to the Agua Dulce Mountains and Organ Pipe Cactus National Monument.  In the June 2013 edition of Herpetological Review, the species was reported from the West Silver Bell Mountains in Ironwood Forest National Monument, which represents a considerable range extension to the east.  In Sonora, its distribution is less well-defined, but it has been found from the Pinacate Region south and east through the deserts, mostly west of Highway 15, to “13 mi SE of Empalme” south of Guaymas. It also occurs on Tiburón and other islands in the Gulf of California.

This is a snake of the Sonoran Desert, where it has traditionally been thought to occur almost exclusively on rocky slopes in desert mountains. However, telemetry work at Organ Pipe Cactus National Monument showed that the Rosy Boa uses adjacent, relatively rock free bajadas and flats (slopes less than 5%) extensively, and often shelters in rodent burrows instead of rocks and boulders. However, habitat use varies seasonally.  Rocky slopes are used for winter retreats and in the early spring, then it moves to adjacent bajadas in late spring and summer. With the summer rains, it uses a variety of micro-sites within its home range, and then moves back to rocky slopes in the fall. Mean home range was 1.6 hectare (calculated for five boas), which is relatively small for a moderate-sized snake. The Rosy Boa occurs from about 350 to 900 m elevation in the 100-Mile Circle.

On warm days in winter, early spring, and fall Rosy Boas may be found out basking during the day, but become more nocturnal as the heat of summer progresses. Morning activity is not unusual in summer.  In our area, most are found from March through November. The species is ovoviparous. Courtship probably occurs in the spring to mid-summer, and litters of one to 12 snakes are born probably during mid-summer to late November. A Rosy Boa collected 29 June near Hermosillo, Sonora contained four embryos that were about two-thirds developed.  The diet of wild Rosy Boas has not been rigorously studied, but captives readily take rodents. Small birds and a Sidewinder have also been consumed by captives. One was observed inside a mine in southern Arizona, possibly hunting bats.

This mostly docile snake is highly sought after by snake enthusiasts.  Destruction of rock shelters, likely as a result of hunting for these snakes, has been documented at Organ Pipe Cactus National Monument.  Road riding records through the Monument suggest that the population along Highway 85 has declined substantially, probably as a result of road mortality. In the last three decades almost no Rosy Boas have been found on Highway 85, but they were reportedly not uncommon in the 1950s.  It is illegal to collect Rosy Boas in Organ Pipe Cactus National Monument or Cabeza Prieta National Wildlife Refuge. Outside of those protected areas, two Rosy Boas may be collected each year and four can be possessed with a valid hunting license. The Rosy Boa is listed as a species of least concern on the IUCN’s Red List.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Ernst, C.H., and E.M. Ernst. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington, D.C.

Grismer, L. 2002. Amphibians and Reptiles of Baja California Including its Pacific Islands and the Islands in the Sea of Cortes. University of California Press, Berkeley.

Parizek, D.A., P.C. Rosen, and C.R. Schwalbe. 1995. Ecology of the Mexican Rosy Boa and Ajo Mountain Whipsnake in a desert rockpile snake assemblage. Final Report to Arizona Heritage Program, Arizona Game and Fish Department, Phoenix.

Parizek, D.A., P.C. Rosen, C.R. Schwalbe, and C.H. Lowe. 1998. Ecology of the Mexican Rosy Boa at Organ Pipe Cactus National Monument, Arizona. Pages 74-75 in T.J. Tibbitts and G.J. Maender (editors), First Conference on Research and Resource Management in Southern Arizona National Park Areas: Extended Abstracts. Organ Pipe Cactus National Monument and Cooperative Park Studies Unit, University of Arizona, Tucson.

Wood, D.A., R.N. Fisher, and T.W. Reeder. 2008. Novel patterns of historical isolation, dispersal, and secondary contact across Baja California in the Rosy Boa (Lichanura trivirgata). Molecular Phylogenetics and Evolution 46 (2): 484-502.

Author: Jim Rorabaugh

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 1988-91 Collected Papers 237-238; 1996 Nov:118.[/vc_column_text][/vc_column][vc_column width=”1/6″][/vc_column][/vc_row][vc_row][vc_column][gap size=”30px” id=”” class=”” style=””][/vc_column][/vc_row]