- Family: Bufonidae
- English: Natterjack Toad
- Scientific: Epidalia (Bufo) calamita
- Spanish: Sapo corredor
- Basque: Apo lasterkaria
- Catalan: Gripau corredor, gripau
- Galician: Sapo corriqueiro
- Portuguese: Sapo-corredor
- Distribution Iberia: Found throughout all Portugal and much of Spain, including the Pyrenees but excluding the northern Atlantic region and the dry central interior, though present in the south.
- Further distribution: UK mainland and Ireland, France through Germany, Switzerland, Denmark and southern Swedish coastal regions to Poland, Belarus, Ukraine and the Baltic states, and also in Northwest Africa and west Asia. In the UK and Eire the species is restricted in its distribution and considered endangered. In Ireland, found only on the Dingle Peninsula, and distribution in the UK is almost restricted to coastal areas.
The Natterjack toad – Epidalia (Bufo) calamita – Sapo corredor is a species of Bufo, a large genus of so-called “true toads” traditionally found worldwide, although some authorities have now separated the Old World species from the New.
Epidalia (Bufo) calamita is a medium-sized toad with a total maximum length of about 9-10cm in Iberia. (Elsewhere in Europe the species is smaller, males measuring 8cm and females 10cm). The head is wider than long, with a short rounded snout, and the area between the eyes is flat. The tympanum, measuring about half the diameter of the eye, is usually not visible, and if it is, only the front part can be seen.
Colouration and pattern are rather variable, the overall colour being shades of brown, grey, yellow or green and a pattern of greenish flecks often being present and usually a yellow dorsal stripe running from between the eyes to the posterior. The warts on the back may be chestnut brown or red in colour. In Iberia the flecks may be larger and more clearly defined, and individuals more often lack the characteristic yellow stripe than elsewhere. The underside is off white to light grey, with dark spots. The iris is lemon yellow to green.
The fingers are short, the third being the longest, followed by the first and the second which are equal in length, and the fourth being the shortest. There are two tubercles on the palms. The dorsal skin has a fair number of largish warts, while the skin on the rear of the belly is granular in texture. The toes are relatively short and flattened.
Epidalia (Bufo) calamita can be easily distinguished from Bufo spinosus (the Iberian spiny toad also present in Iberia) normally by the color of the eyes (normally red in B. spinosus and yellow in Epidalia (Bufo) calamita) but also by the shape of the paratoid glands. In Bufo spinosus these are kidney-shaped, bending inwards somewhat in the middle, while in Epidalia (Bufo) calamita they are straight, being further apart at the front than at the back. Epidalia (Bufo) calamita normally also has a thin yellow stripe down the back which is lacking in Bufo spinosus.
Left: Eye detail of a Natterjack toad. Right: Lifting a stone revealed the daytime hiding place of these two Natterjack toads. (Andalucia)
Across its range the Natterjack toad normally prefers sandy soils and in northern Europe is mainly a lowland animal. However, it can be adaptable: in Spain it can be found in a variety of habitats including arid areas, coastal sands, cultivated fields and mountainous regions.
Feeding and habits
Like most European amphibians the natterjack toad feeds on a variety of invertebrates, but concentrates mainly on arthropods (including various insects and spiders) and less on other invertebrates than the Iberian spiny toad. In Spain, beetles, ants, millipedes, earwigs, grasshoppers and related insects and scorpions have been cited as part of its diet.
The toad is normally a nocturnal animal, coming out at dusk and retiring shortly before dawn, but occasionally may be out in the day, even calling. They may share burrows with other animals or dig their own to a depth of 15-20cm with their forelimbs (and sometimes hind limbs also), or otherwise shelter under stones or logs.
Natterjacks secrete bufotoxin less readily than the Iberian spiny toad, but like the latter resort to the defensive pose in which they stand erect on their limbs and swell their bodies up to make themselves appear much bigger. They also secrete a characteristic smell.
The Natterjack’s gait is also distinctive, being more of a scurrying (likened to that of a mouse) than the hopping or walking normally associated with toads.
Epidalia (Bufo) calamita hibernates on land, as a rule not more than 20m from the original spawning ground (unless it has migrated to a new area) and preferably in a southward-exposed position. The period of hibernation varies with the geographical location and altitude.
In the wild it may be comparatively long-lived, up to 17 years, and in captivity is known to have exceeded this.
The Natterjack’s mating season is longer than that of the other European toads, typically lasting 5-6 months. In Iberia it may begin in December, depending on altitude, and last until June. For example Natterjacks in Southern Portugal may start courting in December, those in the centre in February to March, and those in the mountains in May and June; in Leon, from the end of February until May; and Andalucia from mid-January until the end of March.
Natterjacks have a very loud and distinctive mating call amplified by the single vocal sac found under the chin of the male; their name literally means the “chattering toad” – the jack (toad) that natters (talks a lot).
Unlike the Iberian spiny toads (Bufo spinosus), natterjack toads are not tied strongly to their breeding grounds and do not travel far to them but instead prefer to use shallow, often temporary bodies of water, which have the advantage of having few competitors or predators in them. Males usually call from the banks, singly or in chorus, and the calling cry can be heard at up to 2km distance.
Amplexus is axillary, i.e. the male grasping the female under the armpits. The visiting females do not stay long in the water but lay two long strands of 1,500-7,500 eggs which are usually laid directly on the bottom rather than being attached to vegetation (the latter being the case with Bufo spinosus). The eggs develop within 3-10 days (usually less than a week) and as with the Common Toad the resultant tadpoles may form large swarms. From birth to metamorphosis takes 1-2 months: upon metamorphosis the toadlets are less than 3cm long and more diurnal than the adults.
The breeding season varies according to range. In Portugal it lasts between November and April but lasts until June in the high mountains of the Gredos. The long mating season also allows for more than one clutch of eggs to be laid, up to three a year in some cases: heavy rainfall often triggers mating. Sexual maturity also varies with latitude, taking 3-7 years in northern Europe but in Iberia 3 years for males and 4 for females.
Occasionally hybrids of Bufo spinosus and Epidalia (Bufo) calamita are encountered but they are thought to be sterile as no breeding of the hybrids has been observed.
Threats to the Natterjack toad – Epidalia (Bufo) calamita – Sapo corredor
The most common enemies of the Natterjack are various birds, including not only birds of prey such as some owl species and gulls but also apparently innocuous birds as the sparrow. Colubrid snakes such as the Grass Snake (Natrix natrix) and Viperine Snake (Natrix maura) also prey on Natterjacks and their tadpoles. Tadpoles are also preyed upon by various water invertebrates including the semi aquatic raft spider Dolomedes fimbriatus, which also takes freshly metamorphosed young.
The Natterjack’s longer mating seasons, relatively large eggs and tadpoles, tolerance to warm weather and even brackish water, and ability to emigrate to new areas stand it in better stead to cope with changing conditions than some other amphibians. However, it is adversely affected by the loss of invertebrate diversity in its habitat which reduces the amount of prey available.
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