Artificial shelters
We designed the artificial shelters based on the preferred
nesting/sheltering microhabitat of microhylid frogs, as described by
Felton et al. (2006) for Cophixalus ornatus (now C.
australis ; Hoskin, 2012). Sheltering and nesting microhabitats are
essentially small crevices or holes in soil or wood, or under leaf
litter, logs or rocks. The objective was to make artificial shelters
that contain small spaces and can have a camera inserted to film any of
these spaces (i.e., a ‘chamber’) that is in use.
Two artificial shelter types were constructed, one using wood and one
using concrete. The wooden shelters were made by splitting logs found at
the site (e.g., from a tree fall near a road or path) (Fig. 2A). By
splitting the log in half, we produce a flat surface to place against
the ground (Fig. 2B). The resulting log size (i.e., surface in contact
with the ground) was an average of 60.4 cm in length x 18.5 cm in width.
When a frog occupied the shelter and we decided to film, a 42 mm wide
hole was drilled through the log to fit the camera. The diameter of the
drill hole reflected the size of the end of the camera so that it can be
neatly inserted. We also sourced sink plugs of approximately 40 mm
diameter and filled these with concrete, so that these could be used to
block the hole when the camera was ultimately removed. The concrete was
used to add weight to the plug and to add thermal buffering to the
chamber.
The concrete artificial shelters are rectangular concrete blocks of
(29.5 x 22.5 x 4.5 cm), with six rounded (42 mm diameter) nesting
chambers, each with two entrances/exits (Fig. 3B). A plug hole is
present above each nesting chamber so that the plug can be lifted to
inspect the nesting chamber. The plug sits atop a 40 mm wide and 35 mm
long piece of PVC pipe. The plug has concrete packed into it to better
buffer the nest chamber. We constructed concrete artificial shelters
using a four-two-one concrete mixture (four parts crushed rock; two
parts sand; and one part cement). One-third of the concrete was poured
in a 4 L Tupperware container, and then six 42 mm-wide plastic-wrapped
PVC pipes were equally distributed in the concrete, placed vertically to
make chambers and a galvanized 1 x 1 cm mesh hardware cloth was placed
around them. The other two-third of the concrete was then poured into
the Tupperware container around the PVC pipes. Pieces of garden hoses
(each 3 cm) were placed in the concrete where the entrances/exits going
to be (Fig. 3A). The whole Tupperware container was then placed on a
vibrating plate to remove air bubbles. After drying for at least 48
hours, the PVC pipes and garden hose pieces were taken out of the
concrete. The shelters were then soaked in water for 3 days and then
dried completely in the sun before being deployed in the field. The cost
of making the shelters was AU $20, per mould (4L Tupperware, 42 mm x
100 mm PVC pipe, and 10 pieces of 3 cm garden hose), AU$3 for the
concrete shelter (concrete, sand, crushed rock, and galvanized mesh
hardware cloth) and about AU$18 for the six lids per shelter (sink
plugs, PVC pipe, screws, concrete mixture) (Table 1). So, once you have
the moulds, which are reused, the total cost per shelter is around
AU$21 (US$14), with potential labour costs not included (Table 1).