Mohamed bin Zayed Species project number 240536241

Annual acoustic monitoring of threatened and endemic frog species on the Agulhas Plain - a critical biodiversity hotspot

The Micro Frog (Microbatrachella capensis) is a Critically Endangered species endemic to the south-western Cape region of South Africa. The species is restricted to seven known wetlands across its entire distribution, totaling an occupied area of approximately 10 square kilometres. Four of these wetlands are on the Agulhas Plain. The Micro Frog has been locally extirpated along with much of their wetland habitat due to urban sprawl and alien plant invasion. Cape Lowland Freshwater Wetlands are a nationally recognised vegetation complex and are also considered Critically Endangered. Due to their diminutive size and secretive nature, the species is best studied acoustically by monitoring male advertisement calls.

Past work on the Micro Frog has involved ad hoc aural encounter surveys at 11 sites in four wetlands on the Agulhas Plain, but data on population density and fire-driven dynamics are lacking. In 2023, we determined that the species is no longer present at one of these wetlands, although a previously unknown population was discovered at another wetland in 2021. The species lacks a formal monitoring protocol or species management plan, and the grant will facilitate the development and publication of this crucial document. In 2024, we validated the use of acoustic spatially explicit capture-recapture (aSCR) to monitor this species at seven sites across two wetlands on the Agulhas Plain. A large portion of this area burned in a wildfire in early 2024, creating a fantastic opportunity for post-fire monitoring to assess species recovery following the removal of alien vegetation by fire. 

The specific objectives of this project are as follows: 

1) To confirm the current distribution of the target species - Obtain presence/absence data from replicated surveys at historically known sites where the species has been declared locally extinct;

2) To obtain annual population estimates of the target species - Using acoustic spatially explicit capture-recapture (aSCR), measure densities of calling males;

3) To identify habitat variables driving the relative abundance of the target species - Using N-mixture and occupancy models, quantify the influence of habitat variables on relative abundance (incl. occupancy/distribution);

4) To identify threats to the target species and determine appropriate conservation interventions - Following Objectives 1 and 2, identify negative correlations between habitat covariates and the relative abundance of the target species, then develop management plans to address these threats per species.

The successful execution of this project will contribute significantly towards informing monitoring protocols for threatened, vocalising anurans across southern Africa.