Arizona Black Rattlesnake – Tucson Herpetological Society

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Arizona Black Rattlesnake (Crotalus cerberus)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2147″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Arizona Black Rattlesnake. Photo by Jim Rorabaugh[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2660″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Arizona Black Rattlesnake, Pinal Mtns, Pinal County, AZ. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2661″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Bradshaw Mtns. Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2662″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Female, Bradshaw Mtns. Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2663″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Bradshaw Mtns. Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2664″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Juvenile. Bradshaw Mtns. Photo by Roger Repp[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Arizona Black Rattlesnake (Crotalus cerberus) is a moderately-large (1219 mm TL) snake that is dark gray, dark olive, or dark brown with 25-46 dark blotches and light interspaces between the blotches. The blotches on the body morph into dark bands on the tail, which fade with age. Some populations are darker than others, juveniles (two years of age or less) are considerably lighter-colored than adults, and adults can rapidly (in as little as an hour or less) lighten or darken their dorsal pattern. Juveniles have prominent spots atop the head and a dark bar that runs from behind the eye down and back beyond the corner of the mouth. There are two loreals per side, 161-184 ventral scales, and 16-26 subcaudals. Four or more small internasal scales separate the rostral from the prenasal scales (Lowe et al. 1986, Brennan and Holycross 2006, Amarello and Smith 2009, Rubio 2010, Ernst and Ernst 2012, Davis et al. 2016).

The taxonomy of this species has been and continues to be in flux. Klauber (1956, 1972) and Brattstrom (1964) considered cerberus to be one of nine subspecies of the broad-ranging Western Rattlesnake (Crotalus viridis). Quinn (1987) and Pook et al. (2000), using molecular genetics, identified eastern and western clades of viridis, the latter of which included the Arizona Black Rattlesnake. Ashton and de Queiroz (2001), found the same east-west division and recommended two species be recognized, including C. oreganus(western clade, including C.o. cerberus) and C. viridis (eastern clade). Building on the work of these previous authors, Douglas et al. (2002), using mitochondrial DNA sequences, recommended recognition of seven species within what was formerly C. viridis, including the following snakes that occur in Arizona: Arizona Black Rattlesnake, Prairie Rattlesnake (C. viridis), Midget Faded Rattlesnake (C. concolor), Great Basin Rattlesnake (C. lutosus), and Grand Canyon Rattlesnake (C. abyssus). Schuett et al. (2016) adopted this arrangement for Arizona’s viridis complex. However, Campbell and Lamar (2004) took a conservative approach and, consistent with Ashton and de Queiroz (2001), recognized only C. viridis and C. oreganus (which included the Arizona Black Rattlesnake). When taken together with previous studies, Crother (2008) recognized three of Douglas et al.’s seven (Prairie, Arizona Black, and Western [C. oreganus] rattlesnakes). Brennan and Holycross (2008), Rubio (2010), and Crother (2012) followed Crother’s (2008) arrangement. However, Ernst and Ernst (2012) took an even different approach, and recognized three species within the viridis complex: the eastern clade (C. viridis), a Pacific Coast and Great Basin group (C. oreganus), including five former viridis subspecies (includes the Arizona Black Rattlesnake), and a southern California, Baja California, and adjacent islands group (C. helleri). Herein we follow Crother (2012).

The Arizona Black Rattlesnake, particularly lighter-colored individuals, can be mistaken for other moderate to large rattlesnakes that occur into the foothills and mountains of Arizona. Mojave and Western Diamond-backed Rattlesnakes have conspicuous light and dark banding on the tail. These species and the Black-tailed Rattlesnake usually have three or fewer internasals contacting the rostral. Dorsal scales of Black-tailed Rattlesnakes are usually arranged in 21-23 rows near the tail, whereas the Arizona Black Rattlesnake usually has 19-20 scale rows in that region. The Black-tailed Rattlesnake in our area also has dorsal blotches that usually merge with lateral blotches to form distinctive dark lateral extensions that reach or nearly reach the ventrals. In northern Arizona outside of the 100-Mile Circle, the various forms of the Western Rattlesnake (Crotalus oreganus) can be quite similar to the Arizona Black Rattlesnake and are best distinguished by subtleties of dorsal pattern and distribution (see Brennan and Holycross 2006 and Ernst and Ernst 2012).

In the 100-Mile Circle, the Arizona Black Rattlesnake is known from the Santa Catalina, Rincon, Galiuro, Pinal, Santa Teresa, Gila, Superstition, Mazatzal, and Pinaleño Mountains (Lowe et al. 1986, Brennan and Holycross 2006, Flesch et al. 2010, Bezy and Cole 2014, Davis et al. 2016). It likely occurs in the Winchester Mountains. Reports of the species from the Little Dragoon Mountains and the northern end of the Dragoon Mountains need verification. Elsewhere within its range, the species occurs from south of the Colorado River in Mohave County, Arizona across the Mogollon Rim region and ranges bordering the Rim on the south eastward into Grant County in west-central New Mexico (Lowe et al. 1986, Degenhardt et al. 1996). In the Circle, this is primarily a snake of inland chaparral and montane woodlands – oak, pine-oak, and mixed conifer – at elevations of about 853 m to 2789 m near the top of the Santa Catalinas. But at the lowest elevations, in canyons at the base of mountains, it enters semi-desert grassland and Sonoran desertscrub. Lazaroff et al. (2006) reported reliable sightings of this species on and near the road in the upper reaches of Sabino Canyon in the Sabino Canyon Recreation Area. Arizona Black Rattlesnakes are often found near springs and in riparian areas, as well as places with abundant woody debris, leaf litter, rock outcrops, talus, and boulders (Schofer 2007, Nowak and Arundel undated).

Seasonal activity begins in March or April when snakes emerge from often communal hibernation dens. They will often bask at communal sites and then return to the hibernaculum at night to avoid cold temperatures. No breeding activities occur during these spring aggregations; however, snakes are often selective about snakes with which they associate. Some snakes tend to be loners, while others prefer to be in smaller or larger groups (Amarello 2012, Amarello and Smith 2014). Arizona Black Rattlesnakes can be active by day or at night. Greater nocturnal activity occurs at lower and warmer sites in summer.

Nowak (2005) and Nowak and Arundel (undated) studied Arizona Black Rattlesnake behavior and habitat use at Tonto National Monument. Mean core use area was 4.58 ha for three males. The core use area for a pregnant female was 0.20 ha, and 0.22 ha for a non-pregnant female. Compared to other venomous reptiles, Arizona Black Rattlesnakes were unlikely to be found around human habitations, trails, or other human development. The earliest date a snake entered hibernation was 10 October, the latest was 23 December. Hibernation sites were typically in upland locations in jojoba-mixed scrub or mixed grass-mixed scrub vegetation types. They usually faced north or west; none faced east. The amount of time spent in hibernacula was about two months shorter than Arizona Black Rattlesnakes from the Flagstaff area (Schofer 2007).

Mating occurs in late summer and fall, and generally four to 11 young are born the following summer. A female at Tonto National Monument gave birth to four young in August. Rubio (2010) reported a litter of 21. Female Arizona Black Rattlesnakes and their young remain together for one or two weeks, usually until the young shed their skin for the first time. Neonate snakes are 230-260 mm TL (Klauber 1972, Lowe et al. 1986, Nowak 2005, Nowak and Arundel undated).

The diet of the Arizona Black Rattlesnake is varied, and includes lizards, birds, and mammals (Schuett et al. 2002, Schofer 2007, Loughran et al. 2012, Nowak and Arundel undated, Davis et al. 2016). At Tonto National Monument, items in the diet included a Desert Spiny Lizard, House Finch, Ash-throated Flycatcher, Cactus Mouse, Harris’ Antelope Ground Squirrel, and a White-throated Woodrat (Nowak and Arundel undated). The authors found Arizona Black Rattlesnakes often in association with Velvet Mesquite, and suggested that the seed pods from these trees attracted small mammals that the snakes prey upon.

Most individuals of this species are relatively docile compared to other rattlesnakes in Arizona. However, the venom is 2 to 2.5 times the toxicity of the Western Diamond-backed Rattlesnake (Lowe et al. 1986, Rubio 2010). Any bite from one of these snakes should be considered life-threatening and immediate medical attention should be sought.

The status of this species has not yet been assessed by the IUCN. With a valid Arizona hunting license, four Arizona Black Rattlesnakes can be captured per year or held in possession, alive or dead. This snake is a denizen of mesic montane woodlands and shrublands that are likely to contract as the climate warms and dries out in Arizona (Douglas et al. 2014). Nowak et al. (2014) project a 40% loss of range compared to current conditions, with the most extreme losses of habitat and populations in lower elevation sites.

Arizona Black Rattlesnake (Crotalus cerberus)

Description

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