Biologging is suspect to cause corneal opacity in two populations of wild living Northern Bald Ibises (Geronticus eremita)

Johannes Fritz,Bernhard Goenner,Helena Wehner,Corinna Esterer,Barbara Eberhard,Daniela Trobe,Alexandra Scope,Markus Unsoeld,Bernhard Voelkl

doi:10.1186/s40657-020-00223-8

Abstract

BackgroundIn this paper, we present evidence that biologging is strongly correlated with eye irritation, with sometimes severely impairing effects. A migratory population of the Northern Bald Ibis (Geronticus eremita, NBI) is reintroduced in Europe, in course of a LIFE + project. Since 2014, all individuals have been equipped with GPS-devices. Remote monitoring allows the implementation of focussed measures against major mortality causes.MethodsInitially all birds carried battery-powered devices, fixed on the lower back of the birds. Since 2016 an increasing amount of birds has been equipped with solar-powered devices, fixed on the upper back, the more sun-exposed position. In 2016, we observed opacity in the cornea of one eye (unilateral corneal opacity; UCO) during a regular health monitoring for the first time.ResultsBy 2018, a total of 25 birds were affected by UCO, with varying intensity up to blindness. Clinical examination of the birds revealed no clear cause for the symptoms. However, only birds carrying a device on the upper back were affected (2017 up to 70% of this group). In contrast, none of the birds carrying devices on the lower back ever showed UCO symptoms. This unexpected relationship between tagging and UCO was discovered in 2017. After we took countermeasures by removing the device or repositioning it on the lower back, we observed an immediate reduction of the incidence rate without any new cases reported since January 2019. NBI roost with their head on the back, one eye closely placed to the device if it was positioned on the upper back. Thus, we conclude that the most parsimonious explanation for the symptomatology is either a repetitive slight temperature rise in the corneal tissue due to electromagnetic radiation by the GSM module of the device or a repetitive slight mechanical irritation of the corneal surface. Concrete evidence is missing so far. Meanwhile, cases of UCO were found in another NBI population.ConclusionOur observations indicate that further research in the fast-growing field of biologging is urgently needed. The findings question the positioning of devices on the upper back in birds roosting with the head on the back.

Highlights

In this paper, we present evidence that biologging is strongly correlated with eye irritation, with sometimes severely impairing effects
We describe a hitherto unknown physiological effect, the so-called unilateral corneal opacity (UCO), which occurred in a reintroduced population of the Northern Bald Ibis (Geronticus eremita; Fritz et al 2019) with strong evidence for a causal relationship to biologging
In spring 2017, we recognized a clear relationship between UCO and biologging

Summary

Introduction

We present evidence that biologging is strongly correlated with eye irritation, with sometimes severely impairing effects. The scope of applications steadily increases, conventional radio tracking and remote GPS-monitoring is completed by the measurement and transmission or logging of biological and environmental parameters and even video footage (Bluff and Rutz 2008). As a proprietary animal group for biologging, a common position for external attachment is the lower back, where the device is fixed by various types of leg-loop harnesses. This position was found to be drag-reduced compared to other body positions (Bowlin et al 2010; Pennycuick et al 2012). Solar-powered devices are mainly placed at a more sun-exposed upper back position, fixed by various types of wing-loop harnesses

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