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European Fallow Deer Shifted Activity Toward Dusk During Aerial Culling

European fallow deer standing in dune grass on Norderney, Germany
Research: Behaviour · Conservation: Management

A camera-trap study of invasive European fallow deer (Dama dama) in alpine south-eastern Australia found that helicopter culling was associated with a short-lived shift in when surviving deer were active. Daytime activity declined, while dusk and night accounted for a larger relative share of detections. Grouping and movement speed changed little.

The researchers compared deer behaviour during culling periods with periods without aerial control. In the main analysis, the culling period included the shooting day and the following seven days, so the study tested short-term responses rather than lasting behavioural change.

The clearest response was a shift in daily activity

Activity declined most strongly during daylight and shifted relatively toward dusk and night. The result is more specific than saying the deer simply became nocturnal: daytime activity did not disappear, and the study did not show that the altered pattern persisted beyond the short analysis window.

By contrast, the camera data showed no major change in how deer grouped or in their movement speed. The strongest detectable response to aerial culling was therefore a change in timing rather than a broad behavioural change across all measured traits.

The management value of the response remains to be tested

The authors note that animals surviving aerial control are exposed to helicopters, gunshots and the disturbance of nearby deer being shot. A temporary shift in activity could therefore affect how later control operations encounter surviving animals.

They suggest that future work should test whether the shift toward dusk can be used to improve sustained control. This study itself did not demonstrate that changing the timing or design of helicopter culling would increase the number of deer removed.

Sources and image credit

  1. McCarthy, E. D., Grueber, C. E., Cox, T. E., Lai, B., Tomkins, E., Janes, M., Cass, J., Kuner, C., Whittaker, C., & Newsome, T. M. (2026). Aerial culling alters activity patterns but not grouping or movement in invasive fallow deer. Journal of Applied Ecology, 63, e70249. https://doi.org/10.1111/1365-2664.70249Peer-reviewed primary article first published 14 January 2026. The accessible abstract reports two large camera arrays and a short-term shift from daytime activity toward dusk/night during aerial control, with no major change in grouping or movement speed. Publisher supporting information identifies the Interface and Big Boggy arrays, a 284-km² project area, behavioural monitoring in November 2021–May 2022 and November 2022–May 2023, and defines the main shooting period as the culling day plus the following seven days. Full article text was not accessible in this review.

Image: Stephan Sprinz — European fallow deer in the dunes of Norderney, Germany, 16 June 2024; representative species image, not a deer from the south-eastern Australian study. Source: Wikimedia Commons. · CC BY 4.0 · Source

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