Filling in the gaps: Distribution of the puff adder Bitis arietans (Merrem, 1820) in central South Africa and Lesotho – an investigation using mainly social media records and species distribution modelling

Abstract

The puff adder (Bitis arietans) is widely distributed in Africa and south-western Arabia. Most published records for central South Africa and Lesotho are from surveys undertaken nearly 50 years ago, and although a large part of this area is considered well surveyed, existing occurrence records are sparse with several seemingly inexplicable gaps. Here we investigated the value of photographic and videographic records submitted to social media platforms, especially Facebook, as a source of contemporary geographical distribution data for the region. In addition, we used species distribution modelling to investigate areas of apparent absence. Careful screening and follow-up of Facebook records resulted in many high-quality records (85% of 432 records) with an adequate level of locality accuracy for detailed map plotting. Mapped records indicate that B. arietans is currently widespread in Free State Province, with the exception of a large area in the north. New records confirm that this species still occurs in most areas where it was previously recorded, but its known distribution in the far northern (Deneysville to Bothaville) and south-western (Petrusberg to Fauresmith and Smithfield) parts of the province has greatly increased. The filling-up of apparent gaps in distribution is probably primarily a reflection of better sampling coverage (increased availability of photo-recorded snakes) rather than an indication of recent range expansion. Species distribution modelling based on climatic (precipitation and temperature), elevation and land cover data suggested a high likelihood of suitable habitat for B. arietans throughout most of the study area. A notable exception to this was a largely transformed (mostly crop farming) area in the north of the province that currently lacks both social media and literature records, and which yielded a greatly reduced likelihood of suitable habitat. We contend that this citizen science social media approach represents a valuable tool for investigations of contemporary reptile distributions.