Smoke signals: Measuring wildlife smoke exposure with animal‐borne and stationary sensors

Wildfires are becoming larger, more frequent and more severe, producing smoke plumes that degrade air quality hundreds of kilometres away and for days to weeks after an active fire. Despite public health and safety concerns regarding wildfire smoke, we know little about how free‐ranging wildlife experience or respond to these exposures. This disconnect reflects a serious data gap in the form of sparse air‐quality monitors in the remote landscapes that wildlife occupy. Animal‐borne sensors have revolutionized wildlife ecology by quantifying how individuals respond to environmental stressors in real time, but an equivalent tool for smoke exposure has been missing. Here, we present the ‘smoke logger’, a low‐cost air‐qualiy measurement system for monitoring particulate matter ≤2.5 μm (PM 2.5 ) that uses a laser‐scattering sensor and records sub‐hourly measurements throughout entire fire seasons. The unit can be mounted on a GPS collar, pairing air‐quality measurements with animal location, activity and other biologged data, or deployed as a stationary unit within an animal's home range to characterize ambient exposure to particulate matter associated with smoke and vehicle combustion. Within an urban‐to‐rural gradient, GPS‐collared mule deer ( Odocoileus hemionus ) with attached smoke sensors reported PM 2.5 values that varied with proximity to roads, demonstrating the sensor's ability to resolve fine‐scale pollution gradients. In a remote Utah deployment where the nearest regional monitor was 20 km away, collar readings differed from the nearest network sensor by an order of magnitude, demonstrating the limits of using existing networks to estimate exposure for wildlife research. The smoke logger opens a new pathway for wildlife research by resolving individual‐level smoke exposure at spatial and temporal scales that govern behaviour and physiology. Pairing collar‐measured PM 2.5 with location, activity and physiological measurements allows ecologists to test mechanisms previously only inferred, including behavioural responses to degraded sensory environments during smoke events and sublethal health effects that persist long after visible smoke clears. The open‐source design extends to additional pollutants and microclimate variables (e.g. temperature, humidity, volatile organic compounds), and disagreement between logger readings and regional smoke products may itself be ecologically informative, flagging candidate smoke refugia invisible to coarser monitoring approaches.