Brown Brood Frog

This species is variable and may represent more than one species. It grows to about 30mm in length and is brown, grey, or black above, often with scattered red spots. It is normally strongly marbled black and white on the ventral surface, however in some areas this marbling can be faint. There is always an orange, red or yellow patch in the armpits. This patch varies from yellow to orange between sites. At the Jervis Bay region this patch is always yellow, this may be a result of hybridization with the Dendy's toadlet (Pseudophryne dendyi) which has a strong yellow patch in the armpits. There is also a yellow/orange patch or raised bump on the back of the thigh. Its fingers and toes do not show any webbing nor do they contain any discs. The species has horizontal pupils and the iris displays a gold coloring. The species shows high sexual dimorphism in terms of size. Females are 14% longer than male toadlets and 15% heavier than male toadlets. This is due to the hypothesized longer growing period of female members of the species compared to male members of the species. The cause of female longevity is unknown but it is speculated that it is due to decreased predation risk and increased lifetime expectancy.

The diet of this species is very similar to the diet of another Australian toadlet, Pseudophryne coriacea. They primarily feed on small invertebrates present in leaf litter, such as small ants and greenflys. However, there seems to be no selection in the type of prey that this species will consume. They will consume any arthropod that becomes available to them in the leaf litter present in their habitat. Small black ants are the most common source of food for this species. This species also produces pumiliotoxins (PTXs) that deter predators through their diet. While the mechanism of this acquisition is unknown, consumption of certain alkaloids in their diet allows the toadlet to produce PTXs that deter predators like snakes. These toxins are similar to the compounds secreted by the Poison Dart frogs from South America.

Because of the toxic nature of PTXs, snake species avoid feeding on these frogs. The only real known predator of the P. Bibronii is Limnodynastes peronii, also known as the two striped grass frog. Bones of the Bibron's toadlet have been found in the gut content of two striped grass frogs in the Wallingat State Forest in New South Wales, Australia.