Applying advanced circular statistics: magnetic orientation of green toad larvae

Abstract

Many animals use the Earth's magnetic field as a directional reference. Among those are amphibians, which can be trained towards magnetic directions. We used mixed-effects models, to analyse a dataset exploring magnetic orientation in green toad larvae. We used control simulations with uniform circular distributions to assess whether the modelling approach produced inflated false-positive rates. Traditional approaches applied to average individual bearings, namely the Rayleigh test and Hotelling's test, did not detect significant deviations from uniformity. However, the linear mixed-effects models (LMMs) applied to sine and cosine components suggested orientation components consistent with a trained magnetic response, an untrained magnetic, and a geographic component. Model predictions suggested changing directional responses during the two-minute trial and with the larvae's activity. Larvae oriented geographically northward at the beginning of trials and when activity was high, whereas the trained magnetic response became more pronounced towards the end of trials; the untrained magnetic response was split between NE and SW. Our study represents a first attempt to use recently developed circular adaptations of LMMs with complex random-effects structures to better capture animal orientation strategies, potentially increasing statistical power and providing more nuanced insight into orientation behaviour.