Routine low-altitude overflight crosses the gardens, hedgerows and trees where birds nest and bats hunt. Here’s what the peer-reviewed evidence actually says — including where it stops. This brief takes no position on drones in general; only on routine commercial overflight of homes at scale, before the impact has been assessed and published.
Commercial drone routes are planned to stay clear of roads, motorways and railways — the ground-risk rules under EU drone regulation push flight paths toward lower-traffic ground. In a city, that means residential back gardens, hedgerows and green space. The garden under the corridor plays no part in either end of the delivery; it’s simply the quietest ground to fly over. The corridor is over it by design, not by accident.
When a drone passes low over a nest, birds can flush, stay vigilant instead of feeding, and show spikes in heart rate; in sensitive species that can mean exposed eggs and, at worst, abandoned nests. But the effect is strongly tied to height — and that’s the honest part of the picture.
Manna’s drones operate around 50–80 m — and that figure is measured above sea level, so over raised ground the real height above a nest is lower still, pulling even the higher passes toward the sensitive band. Schematic, from a 2023 meta-analysis of drone disturbance to nesting birds.
Sources · Borrelle & Fletcher 2017; Cantú de Leija et al. 2023; meta-analysis, J. Field Ornithology 2023 (disturbance vs altitude). On drone/noise disturbance generally — none yet study daily commercial delivery overflight.
Bats hunt by sound, and they avoid noisy air. In controlled studies, bat activity dropped by roughly a third and feeding attempts by nearly 40% when noise was introduced overhead — whether the noise masks their echolocation or simply unsettles them. Cork’s gardens — hedges, mature trees, ponds — are exactly where bats feed at dusk through the warmer months. Whether repeated drone passes have the same effect over those gardens hasn’t been studied; the established finding is narrower but clear: bats forage less where there’s noise and movement above them.
Sources · Schaub, Ostwald & Siemers 2008 (“foraging bats avoid noise”); Gilmour et al. 2021 (activity −30%, feeding attempts −38% under added ultrasound).
This isn’t only an ethical point — it’s a legal one. All Irish bat species are strictly protected under the EU Habitats Directive (Annex IV), and wild birds under the Birds Directive and the Wildlife Acts 1976–2018. For protected species the threshold the law sets is disturbance, not proven harm. And under the precautionary principle written into EU law, where there’s credible concern of environmental harm but the science isn’t yet conclusive, the burden sits with the operator to show the activity is safe — not with residents to prove it isn’t.
The question isn’t whether harm has been proven. It’s whether anyone has looked.
We’re not asking anyone to take our word for this. We’re asking for the assessments that should exist before routine overflight of protected habitat — published, so they can be read and tested. As far as we can find, these aren’t on the public record for the Cork flight area:
If they exist, publishing them would settle the question. If they don’t, that’s precisely the gap the precautionary principle is meant to cover.
This brief concerns routine, low-altitude commercial overflight of homes and gardens at scale — not drones, or Manna, in general. It draws only on open, peer-reviewed sources and Irish reporting.
The disturbance research covers survey and deterrent flights, not daily delivery routes. We’ve flagged that gap rather than papered over it — it is the core of the argument, not a weakness in it.
Habitats Directive (Annex IV); Birds Directive; Wildlife Acts 1976–2018; precautionary principle, Art. 191(2) TFEU. Not legal advice.