Visual-acoustic wildlife deterrents as a supporting measure to prevent mowing-related mortality in roe deer fawns

Mowing-related mortality is one of the main causes of death among roe deer
fawns in agricultural regions, prompting farmers in Germany to implement
preventative measures. Understanding the effectiveness of different
deterrent methods is crucial to reducing such mortality. This study
examined the effectiveness of visual-acoustic wildlife deterrent devices
in preventing roe deer fawns from entering agriculturally used areas
before mowing, encouraging those already present to leave, or facilitating
their removal by their mothers. A total of 76 fawns were fitted with
GPS-collars between 2022 and 2023, and their movements were analysed using
a multi-state Markov model.  Our results demonstrate that
visual-acoustic wildlife deterrents significantly influenced fawn
behaviour, with 36% of the fawns leaving the trial area and not returning
at all during the trial period. However, this indicates a substantial risk
of injury or death for the fawns remaining in the fields during mowing.
Among the tested devices, electronic acoustic deterrents, particularly
smoke detectors, were the most effective deterrents, scaring away over 50%
of the fawns without any significant habituation effect.  The
probability of fawns leaving the meadows was further influenced by several
factors such as age, proximity to forest edges, vegetation height, and
field size. Younger fawns, following a "hider" strategy, were
less likely to leave the agriculturally used areas, whereas older fawns
exhibited higher mobility. Fawns more frequently remained in areas with
tall vegetation and large field sizes, while deterrents proved more
effective in smaller fields and near forest edges.  Despite some
success, the limited efficacy of the tested deterrent devices highlights
the necessity for additional measures, such as using drones equipped with
thermal imaging cameras, to further reduce fawn mortality during mowing.
Our findings provide critical insights for improving wildlife management
practices in agricultural landscapes and reducing roe deer fawn losses
during the mowing season.