Predicting spring migration of two European amphibian species with plant phenology using citizen science data

Abstract

Habitat fragmentation is one of the drivers for amphibian population declines globally. Especially in industrialized countries roads disrupt the seasonal migration of amphibians between hibernation and reproduction sites, often ending in roadkills. Thus, a timely installing of temporary mitigation measures is important for amphibian conservation. We wanted to find out if plant phenology can be a proxy in advance to determine the start of amphibian migration, since both phenomena are triggered by temperature. We analysed data of 3751 amphibian and 7818 plant phenology observations from citizen science projects in Austria between 2000 and 2018. Using robust regression modelling we compared the migration of common toads (Bufo bufo) and common frogs (Rana temporaria) with the phenology of five tree, one shrub, and one herb species. Results showed close associations between the migration of common frogs and phenological phases of European larch, goat willow and apricot. Models based on goat willow predict migration of common frog to occur 21 days after flowering, when flowering was observed on 60th day of year; apricot based models predict migration to occur 1 day after flowering, observed on the 75th day of year. Common toads showed weaker associations with plant phenology than common frogs. Our findings suggest that plant phenology can be used to determine the onset of temporary mitigation measures for certain amphibian species to prevent roadkills.

Figure 1

Earliest migration observation of common toads and common frogs and plant phenological phases of common hazel, goat willow and apricot in cool and moderate climate regions in Austria between 2000 and 2018, data missing for some years. Time series of European larch, horse-chestnut, silver birch and snowdrop in Supplementary Fig. S3.

Figure 2

Onset of phenological phases flowering (snowdrop, common hazel, goat willow and apricot) and leaf unfolding (European larch, horse-chestnut, silver birch) and migration start of common toads and common frogs between the years 2000–2018 in Austria.

Figure 3

Correlations between the start of the migration of common toads and common frogs and onset of leaf unfolding of European larch (a), horse-chestnut (b), silver birch (c) and start of flowering of snowdrop (d), common hazel (e), goat willow (f) and apricot (g).

Figure 4

Regression models to predict migration of common frog (model 1 and 2) and common toad (model 3) with flowering of plants labelled. More specific predictions for moderate and cold regions can be derived from models in Supplementary Table S3.