The arroyo toad (Anaxyrus californicus), known for its euphonious call during breeding season, can be mistaken for a cicada to the untrained ear. It was listed as endangered on December 16, 1994. It can be found along the central and southern coast of California to northwest of Baja California, Mexico. Because the arroyo toad inhabits such highly populated and urbanized coastal regions, the species faces a variety of threats to its survival, reproduction and persistence. These threats include non-native predators and plants, disease, water withdrawals, agricultural and urban development, pollution, and natural disturbances (e.g., drought and). In order to protect the Arroyo toad and the areas it inhabits, parks such as Los Padres National Forest, Angeles National Forest, San Bernardino National Forest, and Cleveland National Forest contribute to Arroyo toad recovery by removing non-native predators such as the American bullfrog (Litholbates catesbeianus).
The arroyo toad is a small, warty Anuran that varies in both size and shape during its life cycle. Adult toads can grow to about 2 to 3.5 inches, exhibiting a stocky figure with a blunt snout. Juvenile toads range from 0.4 to 1.6 inches, exhibiting a stocky and oval shaped body, whereas tadpoles range from 0.35 to 1.6 inches, exhibiting a flat body with a tail for swimming.
As adults, arroyo toad coloring is a dark olive, grey or dull brown including warts on top of dark blotches located on the posterior and dorsal side of the body. The anterior side is a whitish color with little to no pattern. Juvenile toads are grey or light brown in color, including little to no blotches and have warty skin with yellow tips. Tadpoles are dark black and begin to lighten to a brown soil-like color with white coloration on the tip of their tails over time. Arroyo toad eyes are a dark brown color with gold on the top and bottom of their irises. Other distinguishable traits include white colored blotches that can be found on their sacral humps and on the front of their parotoid glands as well as a V-shaped white stripe that runs along their head and eyelids.
Arroyo toads have a beautiful call compared to other Anurans. Their call is known for being a long, fast, musical trill that typically lasts about 10 seconds. Although their sound is unique compared to other Anurans, some insect and other toads make similar sounds such as the cicada (Cicada spp.) and the redspotted toad (Bufo punctatus). To the untrained ear, such calls may sound identical, but the essential difference lies in the pitches of the calls, helping experts distinguish singing arroyo toads from other species.
The life cycle of the arroyo toad begins as an embryo that hatches from an egg after four to six days in water temperatures between 54 and 59 degrees Fahrenheit. Then, as a larvae or tadpole, it takes young toads about eight to 14 days (depending on water temperatures) to be able to swim on their own. Once capable, tadpoles swim in short bursts and spread out within their pools, becoming more solitary or dispersed in their distribution. After about nine to 12 weeks, tadpoles metamorphose into toadlets or juvenile toads. At this stage, juvenile toads will stay close to their larval pools for about one to three weeks, but they may remain nearby for up to six months if conditions are favorable. After the first four to five weeks, or whenever juveniles have matured more and grown much larger in size, arroyo toads switch their internal clocks to become nocturnal, allowing them to increase survival by evading common predators. After about one to two years, a male toad officially becomes an adult and sexually mature whereas a female toad does not reach sexual maturity until year 2 or 3. As observed throughout its life cycle, development of the arroyo toad is dependent on water temperatures and food consumption that supports growth and maturation. Without sufficient water temperatures and food sources, underdevelopment or mortality is likely.
The life span of the arroyo toad varies with sex. For males, the average life expectancy is about four years while females live an average of five years.
In central California, breeding usually begins during late March while the southern California breeding season does not begin until January. In addition, breeding events begin after sunset and can last all night long since adults are most active during these periods. The breeding process will begin by males calling in water that is usually around 57 degrees Fahrenheit and about 2 to 4 inches deep. Females will then choose males based on size and call and either copulate right onsite or carry the male higher up a riverbank to do so. The reason for this is because not all riverbanks are suitable for egg clutches to be laid. If conditions are unfavorable, such as lacking proper water and habitat resources, females will forgo laying their eggs. However, whenever a clutch is laid, it is laid on the spot where copulation occurred, consisting of 2,000 to 10,000 eggs that are darkly pigmented, forming two long strings.
One species that the Arroyo toad may get confused with is the California toad (Anaxyrus boreas halophilus). Although their breeding calls are different, physically they look quite similar. However, the California toad does not exhibit facial white lines that form a “V” shape as is found on the arroyo toad. Additionally, arroyo toads do not have white blotches on their parotid glands and sacral humps and instead exhibit distinguishable dark blotches on their anterior side and a pale colored line running down their back.
The arroyo toad’s diet varies with age. As tadpoles, they eat microscopic algae, bacteria, protozoans, detritus and diatoms that live between the pebbles and gravel of their pools. As tadpoles develop into juveniles (e.g., 0.4 to 0.6 inches in length), their diet consists of mostly ants, with the occasional small beetle. This switch toward larger prey allows arroyo toads to consume more protein and macro-nutrients which advances their development. When juveniles become adults (e.g., 2.0 to 3.5 inches in length), they eat fewer ants and, instead, prey on small beetles such as ladybugs.
Adult arroyo toads are mostly nocturnal and remain in their 2-to-4-inch-deep burrows during daytime. However, adults have occasionally been observed at the edges of streams and pools during the day, but only during breeding season. During nighttime, adults leave their burrows to catch prey and to wet their skin. Adult toads travel quickly by hopping with full extension of their legs, a locomotory technique that allows them to travel broad distances. Juvenile toads and tadpoles are mostly diurnal, meaning they are active during the day. They spend their days either in small pools or within proximity of light vegetation. At night, juveniles will use 1-to-2-inch burrows to hide from predators. Typically, adult and juvenile toads congregate in large numbers and are more active during rainfall and humid events. In contrast, tadpoles stay in their pools, but spread out to be less clustered in distribution. During the dry season, adult arroyo toads enter a hibernation-like state called aestivation. This helps prevent their skin from drying up, which keeps the toad alive. During aestivation, they bury themselves in clay or soil-like sand where there is more moisture, allowing their skin to stay damp until the following spring where they emerge to breed.
The arroyo toad requires several unique habitat features in order to flourish. In general, its habitat consists of narrow and shallow aquatic andareas with slow moving water as well as nearby upland areas that are not too widely dispersed. Typical aquatic habitats are bordered by low-elevation hills, scattered vegetation, and sandy, fine gravel, and pliable soils accompanied by rocks of varied size. Younger toads, also known as larvae or tadpoles, tend to inhabit shallow aquatic areas that consist of clay or cobble and sand or gravel. Juveniles, that have already metamorphosized, inhabit sand and gravel bars near the larval pool, especially areas that do not host more than 10% vegetation cover. This is because juveniles can forage in their larval pool for food until it dries while simultaneously prospecting for their next home.
Since the arroyo toad can be found from central California to Baja California, Mexico, several populations experience different climatic and weather conditions at various elevations. During the summer months, temperatures usually range from warm to hot conditions with little or no rainfall. During the winter months, temperatures range from cold to below freezing and include light to moderate rainfall in non-drought periods.
A natural body of running water.
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