This dataset describes environmental conditions at 135 Saiga antelope calving sites (from a total of 214) in Kazakhstan where the predictor variables required for the modelling were available at sufficient resolution. Data collected included climatic variables associated with haemorrhagic septicaemia in the literature, including humidity, temperature and precipitation. Indicators of vegetation biomass, phenology and length of the winter preceding calving were represented using the Normalised Difference Vegetation Index (NDVI), snow depth and snow presence data. Saiga antelope are susceptible to mass mortality events (MME), the most severe of which are caused by haemorrhagic septicaemia following infection by the bacteria Pasteurella multocida. These die-off events tend to occur in May during calving, when saigas gather in dense aggregations. As the bacteria is a commensal organism, which may live harmlessly in the respiratory tract of the saiga, it is believed that an environmental trigger is involved in a shift to virulence in the pathogen or reduction in immune-competence in the host. The attached data show environmental conditions at a set of calving sites of the Betpak-dala population of saigas. This population, one of three in Kazakhstan, is located in the central provinces of the country and is the only one in which massive haemorrhagic septicaemia outbreaks have been recorded. At most of the recorded sites, calving progressed normally, whilst at others mass mortality events occurred during calving or just afterwards, namely in 1981, 1988 and 2015. A set of environmental predictor variables was used to model the probability of an MME at calving aggregations. The dataset, modelling process and results are described in Kock et al. (2018): http://advances.sciencemag.org/content/4/1/eaao2314 A related shapefile of the full set of 214 sites, and metadata concerning site characteristics and the provenance of the location data is available at: https://catalogue.ceh.ac.uk/id/8ad12782-e939-4834-830a-c89e503a298b The attached dataset and site metadata in the above-mentioned Shapefile attribute table can be combined using the variable ID in order to merge the environmental data with information on the calving and MME sites. Full details about this dataset can be found at https://doi.org/10.5285/912ea336-ac90-418f-be6a-7ae226e167e9