Urban Wildlife Nocturnality Shift

City Block

00:00

deep night

Time speed 0.30 h/s

Disturbance

Species baseline

Human disturbance level D 0.00

24-Hour Activity

00:0006:0012:0018:0024:00

Human activity Animal activity

Nocturnality index

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Overlap coeff. Δ

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Animal activity now

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Human activity now

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How it works

Camera-trap studies across six continents (Gaynor et al., Science 2018) found that mammals living near people become measurably more nocturnal — not because night is intrinsically better, but because shifting into the hours when humans are absent lets them keep foraging without constant flight responses. This simulator reproduces that pattern with an avoidance model:

H(t)  = human activity density (bimodal: commute peaks ~08:00 & ~18:00)
A0(t) = species' baseline activity density (crepuscular/nocturnal/diurnal)
A(t)  = A0(t)·exp(−D·k·H(t))   then renormalized
        to the same total daily activity budget

D  = disturbance level (0–1 slider)
k  = species-specific sensitivity to human presence

Raising D exponentially suppresses activity during the hours humans dominate, and the freed-up activity budget is redistributed — mostly into the night — exactly as observed avoidance behaviour does. The nocturnality index is the share of the animal's daily activity falling between 19:00 and 06:00. The overlap coefficient Δ is the classic kernel-density overlap statistic ecologists compute from camera-trap timestamps (Ridout & Linkie, 2009): Δ = ∫ min(H_norm(t), A_norm(t)) dt over the two activity densities, so Δ = 1 means identical schedules and Δ = 0 means fully separated ones. Raccoons, already largely nocturnal, have low sensitivity k and shift little; deer, normally more flexible, show the largest swing.

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