Use of dead tree-fern trunks as oviposition sites by the terrestrial breeding frog Leiopelma archeyi

While most anurans lay their eggs in or near water, there is a wide diversity of species that lay their eggs on the ground, under rocks, or in burrows. For these terrestrial-breeding species, identifying the habitat requirements of oviposition sites is particularly useful for conservation and management planning, given that oviposition in anurans is strongly related to the environmental characteristics in which they live. Leiopelma archeyi is an endemic New Zealand frog that reproduces on moist substrates. Males brood eggs and carry larvae within retreats until metamorphosis is complete. Two previous observations (in November 2014) reported frogs attending eggs inside dead, hollow trunks of tree-ferns (ponga, Cyathea spp. or Dicksonia spp.). We examined whether these observations were random or whether ponga was a breeding resource consistently used by L. archeyi. We used a non-disturbance protocol and focussed on searching inside ponga systematically during three consecutive breeding seasons. This monitoring allowed us to corroborate the reproductive mode previously known for this species and confirm ponga as a recurring oviposition site for L. archeyi. Around 10% of the oviposition sites monitored during the parental-care period were observed with more than one adult inside. Furthermore, we selected three individual ponga known to be used as oviposition sites to mark the centre of a plot from which we measured all ponga trunks. We fitted a mixed-model logistic regression to examine whether the use of ponga as an oviposition site by L. archeyi was predicted by length and/or diameter at the opening of the trunk. However, neither of these trunk characteristics were useful predictors for the use of ponga as an oviposition site. Our observations raise questions about the reproductive mode of this species such as oviposition site fidelity, and interactions within a community level between two ancestral lineages (Leiopelmatidae and tree ferns).