Kōrero: Frogs

Whārangi 4. Ecology and reproduction

Ngā whakaahua me ngā rauemi katoa o tēnei kōrero

Native frog habitats

The native frogs are terrestrial (living on land) or semi-terrestrial, and none lay their eggs in water. They are all well camouflaged and stay in retreats under logs, stones or in vegetation during the day. This helps retain moisture and reduce the risk from predators.

Some live on misty ridge-tops far from surface water.

Only Hochstetter’s frog is semi-aquatic, tending to stay close to streams. It is also the only one with partial webbing between the hind toes. The other three species are forest dwellers, although Hamilton’s frog is mainly restricted to a 600-square-metre boulder bank on Stephens Island – surely the smallest known habitat for any frog. The Maud Island frog reaches densities of five frogs per square metre in suitable places.

Archey’s frog is terrestrial but may climb several metres into trees and bushes during the night, before returning to its retreats at dawn. The Whareorino Forest population in the King Country, discovered in 1991, may spend more time in trees than the Coromandel groups.

Humidity

All frogs need a moist environment to keep their skin damp, as they breathe through their skin as well as their weak lungs. The native frogs are more likely to be seen at night when the humidity is high, or after rain. Archey’s frog is able to withstand substantial drying. One study showed that frogs that were dehydrated to 92% of their body weight increased hydration to 99% over four hours when placed on wet leaves. Climate change could have a profound effect on the native frog populations if it leads to dryer conditions in some areas.

Habitats of the introduced frogs

The introduced Australian bell frogs usually live near water, but the whistling frog is not as restricted. Whistling frogs are nocturnal, but both the bell frogs may be active during the day or night, and sometimes sunbathe in the afternoon.

Feeding

All the frogs feed on any invertebrate prey that they can take hold of and ingest. The native frogs take prey directly into their mouths, sometimes using their arms. Introduced frogs tend to use their highly extensible fast-flicking tongues to capture prey.

Finding a mate

The native Leiopelma frogs do not make loud mating calls like other frogs, but may find each other by using visual cues or through pheromones (chemical signals between animals). Research has shown that the Maud Island frog can respond to the scent cues in frog faeces. Males of the introduced species call or croak to attract females.

Mating

Frog mating is called amplexus. In the native Leiopelma species, amplexus is inguinal: males clasp the females around the ‘waist’. In the three introduced species amplexus is axillary: males grasp the females around their armpits.

Egg laying and care

Native frogs

All four native species produce very large yolky eggs (between 1 and 22, depending on species). Female Hochstetter’s frogs lay their eggs under stones or fallen vegetation. Researcher Joan Robb has also found clutches laid in tunnels bored by the larvae of the large Uropetala carovei dragonfly.

Hochstetter’s frogs give no parental care – the tailed froglets hatch out, absorb the yolk, and resorb (assimilate) their tail.

The other three Leiopelma have very similar reproductive behaviour. Females lay small clutches of large eggs, which the males sit over until they hatch. Young froglets, complete with yolk sac and tails, climb onto the male’s back and stay there for a month or longer until they become independent. Such care may keep the youngsters moist, reduce predation and possibly reduce fungal or microbial infections.

Introduced frogs

The introduced frogs lay large numbers of eggs in water and leave them to fend for themselves. Tadpoles stay in the water until metamorphosis approaches: the tiny, tailed froglets leave the water for long periods, and eventually become frogs.

Me pēnei te tohu i te whārangi:

Paddy Ryan, 'Frogs - Ecology and reproduction', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/frogs/page-4 (accessed 8 December 2019)

He kōrero nā Paddy Ryan, i tāngia i te 24 Sep 2007