A heuristic method to evaluate consequences for flight control and stability induced by attachment of biologging devices to birds and bats

Abstract Biologging is central to the study of wildlife, but questions remain about the minimization of effects of biologging devices. Rarely considered are changes biologging devices induce on an animal's centre of mass (COM) and resulting losses of flight control and stability. We applied established aeronautical principles to estimate how the COM of a flying bird or bat may be affected by the typical positioning of a biologging device on the neck, back, hips or tail. We then adopted modified thresholds from aerospace engineering to estimate limits beyond which changes to COM result in fitness‐relevant alterations to flight control and stability. Generic models illustrate a trade‐off between the placement and mass of a biologging device that influences flight control and stability. Seven species‐specific examples show the substantial differences in consequences of changes to COM for animals of different sizes and body types. Placement of a device on the tail always resulted in the greatest shift in COM and placement in the centre of the back resulted in the smallest shift. The 5% weight threshold some use for a biologging device provides little room for error in terms of stability and can easily cause dangerous changes to COM. The 3% weight threshold others use causes considerably smaller changes in the COM, but when placed away from the natural COM, still can affect flight control and stability. Researchers interested in minimizing the effects to fitness of wildlife should consider weight, balance and COM when affixing biologging devices. The farther a device is from the natural COM, the smaller it should be relative to the mass of the animal.