Frequency-dependent tolerance to aircraft disturbance drastically alters predicted impact on shorebirds

Anthropogenic disturbance of wildlife is increasing globally. Generalizing impacts of disturbance to novel situations is challenging, as the tolerance of animals to human activities varies with disturbance frequency (e.g. due to habituation). Few studies have quantified frequency-dependent tolerance, let alone determined how it affects predictions of disturbance impacts when these are extrapolated over large areas. In a comparative study across a gradient of air traffic intensities, we show that birds nearly always fled (80%) if aircraft were rare, while birds rarely responded (7%) if traffic was frequent. When extrapolating site-specific responses to an entire region, accounting for frequency-dependent tolerance dramatically alters the predicted costs of disturbance: the disturbance map homogenizes with fewer hotspots. Quantifying frequency-dependent tolerance has proven challenging, but we propose that (i) ignoring it causes extrapolations of disturbance impacts from single sites to be unreliable, and (ii) it can reconcile published idiosyncratic species- or source-specific disturbance responses.

The assemblage of birds struck by aircraft differs among nearby airports in the same bioregion

Abstract ContextBird–aircraft collisions impose an economic cost and safety risk, yet ecological studies that inform bird hazard management are few, and to date no study has formally compared species’ strike profiles across airports. In response to strike risks, airports have implemented customised management on an airport-by-airport basis, based on the assumption that strike risk stems from prevailing local circumstances. We tested this assumption by comparing a decade of wildlife–aircraft strikes at three airports situated in the same bioregion (likely to have similar fauna) of Victoria, Australia. AimTo compare the assemblage of wildlife struck by aircraft at three major airports in the same bioregion. MethodStandardised wildlife strike data were analysed from three airports (Avalon, Melbourne and Essendon Airports), in the Victorian Volcanic Plains bioregion, central Victoria, Australia. Ten discrete 1-year sampling periods from each airport were compared, spanning the period 2009–19. Bird data were comparable, and data on mammals were considered less reliable, so emphasis was placed on birds in the present study. ResultsIn total, 580 bird strikes were analysed, with the most commonly struck species being Australian magpie (Cracticus tibicen; 16.7%), Eurasian skylark (Alauda arvensis; 12.2%), Australian pipit (Anthus australis; 12.1%), masked lapwing (Vanellus miles; 5.9%), nankeen kestrel (Falco cenchroides; 5.0%), house sparrow (Passer domesticus; 4.8%), welcome swallow (Hirundo neoxena; 4.3%) and tree martin (Petrochelidon nigricans; 4.0%). The assemblage of birds struck by aircraft over the decade of study differed between airports. The most commonly struck species drove the assemblage differences between airports. Conclusions and implicationsIn the present study system, airports experienced discrete strike risk profiles, even though they are in the same bioregion. The airports examined differed in terms of air traffic movement rates, aircraft types, landscape context and bird hazard management effort. Given that strike risks profiles differ among airports, customised management at each airport, as is currently the case, is supported.

Urban noise restricts, fragments, and lightens sleep in Australian magpies

Urban areas are inherently noisy, and this noise can disrupt biological processes as diverse as communication, migration, and reproduction. We investigated how exposure to urban noise affects sleep, a process critical to optimal biological functioning, in Australian magpies (Cracticus tibicen). Eight magpies experimentally exposed to noise in captivity for 24-h spent more time awake, and less time in non-rapid eye movement (non-REM) and REM sleep at night than under quiet conditions. Sleep was also fragmented, with more frequent interruptions by wakefulness, shorter sleep episode durations, and less intense non-REM sleep. REM sleep was particularly sensitive to urban noise. Following exposure to noise, magpies recovered lost sleep by engaging in more, and more intense, non-REM sleep. In contrast, REM sleep showed no rebound. This might indicate a long-term cost to REM sleep loss mediated by noise, or contest hypotheses regarding the functional value of this state. Overall, urban noise has extensive, disruptive impacts on sleep composition, architecture, and intensity in magpies. Future work should consider whether noise-induced sleep restriction and fragmentation have long-term consequences.