This species is endemic to the Wet Tropics Bioregion (Williams and Hero 1998, 2001) from Paluma to Cooktown, north Queensland, at altitudes between sea level and 1,200m asl (McDonald 1992). The species includes two divergent genetic lineages separated by Barron Creek-the diversity within each lineage is very low (M. Cunningham pers. comm.).
Habitat and Ecology
This species is a rainforest specialist (Czechura, Ingram and Liem 1987). In montane areas the species prefers fast-flowing rocky streams although they also frequent slower watercourses where ample vegetation exists along the margins (Czechura, Ingram and Liem 1987). At low elevations, it favours rock soaks, narrow ephemeral streams and rock outcrops in larger watercourses (Czechura, Ingram and Liem 1987). It may also be found on rocks, boulders and vegetation in or adjacent to streams (Czechura, Ingram and Liem 1987). N. dayi is a spring and summer breeder (Davies and Richards 1990) with peak breeding activity from October to April (Hero and Fickling 1997; Hodgkinson and Hero 2002). Davies and Richards (1990) provide a detailed description of the developmental biology of the species. Males call at night from rocks and low foliage along rapidly flowing stretches of creek. The competition for females may necessitate territorial behaviour in males, as they have never been found calling in a group or within 1m of another male (Hodgkinson and Hero 2002). Amplexus is axillary and eggs are laid in a cohesive clump under rocks in rapidly flowing water (Czechura, Ingram and Liem 1987). One clutch collected contained 107 unpigmented eggs (egg diameter 2.3-2.6mm, capsule diameter 3.3-3.5mm, n=5) (Davies and Richards 1990). Larvae can be found on or under rocks in fast-flowing sections of stream and show adaptations to living in torrents, such as large suctorial mouthparts and muscular tails (Davies and Richards 1990; Fickling and Hero 1994). After hatching they aggregate under a rock until their digestive tracts are fully formed (Davies and Richards 1990). After several days they begin to graze on benthic algae and may drift downstream. Larvae from eggs laid in early summer complete development in 3-4 months, while those eggs laid in late summer may overwinter and metamorphose the following summer (Davies and Richards 1990).
Nyctimystes dayi has disappeared from upland sites throughout the Wet Tropics and was last recorded from Mount Spec State Forest in 1990 and the Kirrama Range in 1989 (Richards, McDonald and Alford 1993; M. Cunningham pers. comm.). Richards, McDonald and Alford (1993) noted that the species was still common at most foothill and lowland sites and recorded adults and larvae from upland sites north of the Daintree River. These populations subsequently disappeared in 1992 and 1993 (M. Cunningham pers. comm.). At one monitoring site at O’Keefe Creek, Big Tableland, this species has occasionally reappeared near a site at an altitude of 400m asl, but it has not established resident populations and is absent from a monitoring site at 680m asl (McDonald and Alford 1999). Interestingly, the lowland and foothill populations still exist (McDonald and Alford 1999).
The reason(s) for the decline of the species are largely unknown. Although in the past habitat destruction may have been a factor, clearing or logging has not taken place in the Wet Tropics World Heritage Area, where the species occurs, since 1988 (McDonald and Alford 1999). Richards, McDonald and Alford (1993) first noted a decline of the species in pristine rainforest habitats in 1989. Richards, McDonald and Alford (1993) reject drought, floods, habitat destruction or changes in water quality (pH, conductivity, temperature, dissolved oxygen and metal ions) as the primary causes of the decline. However, in a study by Hodgkinson and Hero (2002) cold temperatures were found to reduce the activity of N. dayi and it was suggested that prolonged exposure to cold, dry conditions (particularly at high altitudes) may inhibit the breeding and survival of the frogs and influence recruitment in local populations. Current research is examining the possibility that disease, possibly a virus or chytrid fungus, may have contributed to the decline of this species (Berger, Speare and Hyatt 1999; McDonald and Alford 1999). Chytrid fungus was detected in this species in Tully, Queensland. Feral pigs are a potential cause of riparian habitat damage and adult frog mortality (Richards, McDonald and Alford 1993). The activity of feral pigs has been recorded to have increased over the period 1989-1992 in an area previously inhabited by N. dayi (Richards, McDonald and Alford 1993). However, there has been very little research into the impact of feral pigs on native frog populations (Richards, McDonald and Alford 1993).
The range of the species includes several protected areas. Although a recovery plan is in place for this species, further research into the cause of the decline of this species is necessary.
Jean-Marc Hero, Ross Alford, Michael Cunningham, Keith McDonald, Richard Retallick 2004. Litoria dayi. In: IUCN 2014