Grey Barred Frog

Population and DistributionMixophyes balbus is restricted to the e. slopes of the Great Divide, from the Cann R. catchment in far East Gippsland, Vic., to tributaries of the Timbarra R. near Drake, NSW (Gillespie & Hines 1999). The area of occurrence of the species is about 110 000 km2 (map in Gillespie & Hines 1999). The species occurs from 20 to over 1400 m altitude, from low to high altitudes from s. to n. (Gillespie & Hines 1999). Mixophyes balbus was formerly more frequently encountered in the n. part of its range than s. of Sydney, although this may reflect limited historic searches in the region (Gillespie & Hines 1999). The species has only been found in Vic. on three occasions (Tennyson Ck, Cann R. and Jones Ck) and is now thought to be extinct in that state (Gillespie & Hines 1999). The species has declined and disappeared from a number of locations in NSW where it was common (Mahony 1993; Anstis & Littlejohn 1996; Anstis 1997). Surveys in s.e. NSW since 1990 have located individuals at only a few sites (Lemckert et al. 1997; Daly 1998). While actual estimates of population size are not available, where populations have been recorded recently, the species appears to be in low numbers (Mahony et al. 1997). Mixophyes balbus is known from Blue Mt, Coopracambra, Dorrigo, Gibraltar, Morton, New England, Washpool and Werrikimbee NP, Bulahdelah, Carrai, Chaelundi, Dampier, Ellis, Forestlands, Hyland, Malara, Marengo, Mt Boss, Mumbulla, Myall R., Olney, Strickland, Watagan and Wild Cattle Ck. SF (Tyler 1997), Barrington Tops, Junuy Junuum, Myall L. NP, Awaba, Barrington Tops, Chichester, Doyles R., Giro, Heaton, Kerewong, Lorne, Middle Brother, Ourimbah, Styx R., Wang Wauk, Wyong SF (F. Lemckert pers. comm.), Butterleaf, Ewingar, Girard, Malara, Moogem SF (K. McCray pers. comm.).HabitatMixophyes balbus is typically found in association with permanent streams through temperate and sub-tropical rainforest and wet sclerophyll forest, rarely in dry open tableland riparian vegetation (Mahony et al.1997), and also in moist gullies in dry forest (Gillespie & Hines 1999). The ecological requirements of adults and larvae are poorly known. In n.e. NSW, statistical modelling was used to investigate the relationship of M.balbus with 24 environmental predictors (NSW NPWS 1994 in Gillespie & Hines 1999). The species showed a preference for the interiors of large forest tracts in areas with relatively cool mean annual temperatures. These sites are typically free from any disturbance with a thick canopy and relatively simple understorey (Gillespie & Hines 1999). Mixophyes balbus occurs along first order streams and occasionally associated with springs (Mahony et al. 1997). The species is not associated with ponds or ephemeral pools (Mahony et al. 1997). Tadpoles do occur with several species of native fish (Mahony et al. 1997).

ReproductionCalling has been recorded from Sep. to Apr. (F. Lemckert pers. comm.). Males call from beside small streams, often from under leaf litter or within holes (Lemckert & Morse 1999). Reproductive biology is very similar to that of Mixophyes fleayi (Gillespie and Hines 1999). Both species construct a nest in the shallow running water that occurs between pools in relatively wide, flat sections of mountain streams (Knowles et al. 1998). 500-550 pigmented eggs (2.8mm diameter) are deposited in a shallow excavation in the stream bed or pasted directly onto bed rock (Watson & Martin 1973; Knowles et al. 1998; Knowles pers. comm in Daly 1998). The stream microhabitats used by this species for oviposition are limited (Knowles et al. 1998). The free-swimming tadpole of the species has been described by Watson and Martin (1973) and Daly (1998). Tadpoles develop in pools and shallow water with the aquatic phase of the life cycle lasting approximately one year (Daly 1998). Invasive speciesTrampling by domestic stock is likely to have deleterious impacts on oviposition sites of the species (Knowles et al. 1998). Mixophyes balbus tadpoles have been found in sympatry with native fish, and probably have survival strategies to avoid predation from them (Gillespie & Hines 1999). However, the impact of introduced fish, such as Eastern Gambusia (Gambusia holbrooki), carp (Cyprinus spp.) and salmonids is unknown (Gillespie & Hines 1999). Mahony et al. (1997) did not observe introduced fish at any sites where they found M. balbus. In other reports though, introduced fish (salmonids) have been recorded at sites where M. balbus has declined (Anstis 1997). However, M. balbus has also disappeared from many streams which do not contain introduced fish species (Gillespie & Hines 1999). MovementsOn several occasions during rainfall events individuals have been found on roads (Mahony 1993; Lemckert & Morse 1999) at least 100 m away from the nearest waterbody suggesting that individuals move widely through the forest when moist conditions prevail (Lemckert & Morse 1999).

Several potentially threatening processes have operated at sites where M. balbus has been found, or up-stream in catchments. Logging and associated forest management practices have been carried out in some catchments where M. balbus historically occurred, or currently occurs (Mahony et al. 1997). The health and stability of extant populations in these disturbed catchments is unknown. Forest grazing and land clearance for pasture upstream have also occurred in some catchments (Mahony et al. 1997). Mahony et al. (1997) report that the species is not known from any localities with disturbed riparian vegetation or significant human impacts upstream. This may indicate that the species is highly sensitive to perturbations in the environment. However, populations of this species have also disappeared in catchments with seemingly minimal human disturbance (Mahony et al. 1997). [Gillespie and Hines 1999]

Breeding occurs from September to April (4). Males call from the edges of small streams, from under leaf litter or within holes, making a soft, short, pulsed call, 'kook kook kook kra-a-ak kruk kruk' that last for just a couple of seconds (2). A nest is constructed in shallow running water and between 500 and 550 coloured eggs are deposited in a shallow excavation in the stream bed. The tadpoles develop in pools and shallow water where they remain for up to one year, depending upon when the eggs are laid (1) (4).

The stuttering frog is found in more than 20 national parks (4), and is the subject of a recovery plan which aims to determine the factors causing the decline in numbers, at the same time as researching and maintaining the current populations (5). A three year research programme has just been completed which assessed the distribution and abundance of this species, as well as its ideal habitat vegetation and water quality (5). There is also ongoing monitoring of the stuttering frog at a number of sites by researchers at the Australian University of Newcastle (4).

So named due to the stuttering sound of its call, the stuttering frog is a large, well-built frog with strong hind limbs. It has mid to dark brown bars on the hind limbs and a dark line running from the eye towards the shoulder against the yellow-grey skin (2) (3). The eye has a blue crescent under the upper lid (2). The tadpoles are large with dark grey bodies, and dark grey fins with black speckling (2).

Occupying permanent streams through temperate and sub-tropical rainforest, the stuttering frog is also found in the moist gullies of dry forest (1).

The stuttering frog is found from northeast Victoria to New South Wales, Australia (3), in a range of 110,400 km² (1). It occupies low altitudes in the south and high altitudes in the north (1).

The stuttering frog is classified as Vulnerable (VU C1 + 2a(i)) on the IUCN Red List 2004 (1). It is listed under Schedule 1 of the Threatened Species Conservation Act of Australia (3).

Habitat fragmentation and degradation as a result of forest grazing and land clearance for agriculture has isolated populations of the stuttering frog (1) (3). These small, isolated populations risk local extinctions as they become more vulnerable to catastrophic events, such as wildfires, droughts or disease, as well as to reduced fitness through inbreeding (4).

Mixophyes balbus Straughan

MATERIAL.—UMMZ 154850 (two specimens dissected, stage 25, SVLs 16.9, 17.1 mm). No locality data.

REFERENCE.—Watson and Martin (1973) described the external morphology.

GENERAL

The stuttering frog (Mixophyes balbus) is a large species of frog that inhabits temperate and sub-tropical rainforest and wet sclerophyll forest in Australia.