Agile Frog - Ecology

Agile Frog - Ecology

Species: The Agile frog (Rana dalmatina) is unique in Jersey and is found nowhere else in the British Isles. It is no surprise that these frogs get their name as they are slim, with unique long stripey hind legs. Adults can grow up to 9cm, snout to vent length (SVL) and can jump up to a staggering 2 meters. This is particularly important when escaping from predation such as domestic cats which is a huge problem for almost every island native species. Whereas frogspawn is at risk by waterfowl (ducks) and non-native fish. They can be characterised by dark eye masks, with silver/gold markings around the oval and a horizontal pupil. Body colour varies with pinkish brown to yellow and a pale underside (ventral) with black blotches on the back (dorsal). Females are slightly bigger than males, this can help people distinguish sex as both look remarkably similar in appearance, this is called sexual dimorphism (JARG, 2020). 

Habitat and diet: In Jersey, the surviving Agile frog population is found by the Coastal Heath and Gorse habitats of the Southwest. They can be found migrating to ponds from February and then seen on land again between April/May-October. Hibernation usually takes place between November–January/February. An adults diet includes invertebrates such as small flies and their larvae, beetles, and earthworms. Whereas tadpoles will primarily feed on detritus and aquatic plants as well as animal matter.  

Reproduction: Like most amphibians they have complex life cycles that rely both on aquatic and terrestrial environments. The Agile frog will spawn between mid-February to early April. With a type of mating behaviour called amplexus (Latin for “embrace”) this is when males grasp on the back of females and externally fertilize the eggs. However, due to milder winters breeding may occur earlier in January. These eggs are deposited under water in round clumps, usually on underwater vegetation, plant stems and twigs. Spawn clumps are laid around plant stems in shallow waters. In Jersey this species is historically found in woodland but is now restricted to coastal heathland breeding in shallow ponds in scrub. Temperature will decide the development of the tadpoles before hatching. A process called metamorphosis occurs taking 2 to 4 months in which froglets appear and can be seen from late May/June (figure, lifecycle). Air temperature and day length are main attributes for spawning as frogs can breed in colder temperatures (5oC) than toads (7oC) (Ben Hoare, 2015; BBC Wildlife Magazine, 2020; National Trust for Jersey, 2020). 

Photo credit: Piers Sangan

Agile Frog