The roar of the tiger stream treefrog Hyloscirtus tigrinus: advertisement call, distribution update, novel colouration patterns and comments on natural history

Hyloscirtus tigrinus is a rare, Endangered and colourful stream treefrog inhabiting the paramos and high Andean forest of south-western Colombia and northern Ecuador. During 2021–2023, we undertook fieldwork in Colombia at the Puracé National Park and surrounding areas, which yielded observations on the distribution, behaviour, advertisement call, colour pattern variations and phylogeny of this species. We report two new localities for H. tigrinus, which extends the north-eastern margin of its range by 18 km and gives a total of 10 known localities; these are restricted to between 2,638–3,470 m a.s.l.. Recordings of the male advertisement call indicate a single low-pitched pulsed note without frequency modulation, composed of two to six pulses. The call is emitted at a rate of 37.8–48.3 calls/min, with a dominant frequency between 1,636.52–1,894.92 Hz, and resembles that of Hyloscirtus larinopygion and Hyloscirtus antioquia, but H. tigrinus shows a lower number of pulses per call. Like other Hyloscirtus spp., the passive defensive behaviour of the species may include immobility, crouching and contraction. The populations from the new localities exhibit a light brown to reddish-brown dorsal colouration with black reticulate pattern or scattered blotches, which represents the most divergent colouration observed in the species. Phylogenetic and morphological analyses provide evidence that the most northerly populations, which exhibit divergent colouration, belong to H. tigrinus. Genetic distances for gene 16S (0.293–0.298%), indicate they are closely related to populations from Ecuador but remain distinguishable from them.