The common name “Marine Toad” and the scientific name Bufo marinus suggest a link to marine life, but the adult cane toad is entirely terrestrial, only venturing to freshwater to breed.
Tadpoles have been found to tolerate salt concentrations equivalent to at most 15% that of seawater.
The cane toad inhabits open grassland and woodland, and has displayed a “distinct preference” for areas that have been modified by humans, such as gardens and drainage ditches.
In their native habitats, the toads can be found in subtropical forests, although dense foliage tends to limit their dispersal.
The cane toad begins life as an egg, which is laid as part of long strings of jelly in water. A female lays 8,000–25,000 eggs at once and the strings can stretch up to 20 metres (66 ft) in length.
The black eggs are covered by a membrane and their diameter is approximately 1.7–2.0 mm (0.067–0.079 in).
The rate at which an egg evolves into a tadpole is dependent on the temperature: the pace of development increases with temperature. Tadpoles typically hatch within 48 hours, but the period can vary from 14 hours up to almost a week.
This process usually involves thousands of tadpoles—which are small, black and have short tails—forming into groups. It takes between 12 and 60 days for the tadpoles to develop into toadlets, with four weeks being typical.
Similarly to their adult counterparts, eggs and tadpoles are toxic to many animals.
When they emerge, toadlets typically are about 10–11 mm (0.39–0.43 in) in length, and grow rapidly. While the rate of growth varies by region, time of year and gender, Zug and Zug found an average initial growth rate of 0.647 mm (0.0255 in) per day, followed by an average rate of 0.373 mm (0.0147 in) per day. Growth typically slows once the toads reach sexual maturity.
This rapid growth is important for their survival—in the period between metamorphosis and sub–adulthood, the young toads lose the toxicity that protected them as eggs and tadpoles, but have yet to fully develop the parotoid glands that produce bufotoxin. Because they lack this key defence, it is estimated that only 0.5% of cane toads reach adulthood.
As with rates of growth, the point at which the toads become sexually mature varies across different regions. In New Guinea, sexual maturity is reached by female toads with a snout–vent length of between 70 and 80 mm (2.8 and 3.1 in), while toads in Panama achieve maturity when they are between 90 and 100 mm (3.5 and 3.9 in) in length.
In tropical regions, such as their native habitats, breeding occurs throughout the year, but in subtropical areas, breeding occurs only during warmer periods that coincide with the onset of the wet season.
The cane toad is estimated to have a critical thermal maximum of 40–42 °C (104–108 °F) and a minimum of around 10–15 °C (50–59 °F). The ranges can change due to adaptation to the local environment.
The cane toad has a high tolerance to water loss—one study showed that some can withstand a 52.6% loss of body water, allowing them to survive outside tropical environments.
Diet:
Most frogs identify prey by movement, and vision appears to be the primary method by which the cane toad detects prey; however, the cane toad can also locate food using its sense of smell.
They eat a wide range of material; in addition to the normal prey of small rodents, reptiles, other amphibians, birds and a range of invertebrates, they also eat plants, dog food and household refuse. Cane toads have a habit of swallowing their prey.
Defences:
The adult cane toad has enlarged parotoid glands behind the eyes, and other glands across their back. When the toads are threatened, their glands secrete a milky-white fluid known as bufotoxin. Components of bufotoxin are toxic to many animals; there have even been human deaths due to the consumption of cane toads.
Bufotenin, one of the chemicals excreted by the cane toad, is classified as a Class 1 drug under Australian law, alongside heroin and cannabis. It is thought that the effects of bufotenin are similar to that of mild poisoning; the stimulation, which includes mild hallucinations, lasts for less than an hour.
As the cane toad excretes bufotenin in small amounts, and other toxins in relatively large quantities, toad licking could result in serious illness or death.
In addition to releasing toxin, the cane toad is capable of inflating its lungs, puffing up and lifting its body off the ground to appear taller and larger to a potential predator.
Predators:
Many species prey on the cane toad in its native habitat. These include the Broad-snouted Caiman (Caiman latirostris), the Banded Cat-eyed Snake (Leptodeira annulata), the eel (family: Anguillidae), various species of killifish,
the Rock flagtail (Kuhlia rupestris), some species of catfish (order: Siluriformes) and some species of ibis (subfamily: Threskiornithinae). Predators outside the cane toad’s native range include the Whistling Kite (Haliastur sphenurus), the Rakali (Hydromys chrysogaster), the Black Rat (Rattus rattus) and the Water Monitor (Varanus salvator).
There have been occasional reports of the Tawny Frogmouth (Podargus strigoides) and the Papuan Frogmouth (Podargus papuensis) feeding on cane toads. It is likely that an opossum of the Didelphis genus can eat cane toads with impunity.
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