Brown frog breeding phenology in south Sweden 1990 – 2017: are data subsets robust?

Abstract

- Field data on breeding phenology of Ranaarvalis and R.temporaria for the period 1990- 2017 in Scania, Sweden are presented and analysed. There was no temporal trend for R.temporaria. ForR.arvalisthe results were mixed, one out of two approaches found a trend to earlier breeding. The lack of a consistent trend in breeding phenology is unsurprising considering that local mean air temperatures in February, March and April showed no significant trends over the study period. To test the robustness of the conclusion, different subsets of the data (years or ponds) were also analysed for trends. For most subsets the conclusions remained the same. Possible bias arising from the choice of which years to include in an analysis of trends is discussed.