Within the Sound of…Humans
It is deep winter where I live. In my little office, I sit tucked into a woollen blanket that once kept my aunt and uncles warm during their childhood in rural Victoria. As I write, I can hear the calls of various bird species, their vocalisations made difficult to distinguish over the gentle hum of my winter companion: a small electric heater. I have just finished an online class, during which I needed to turn off my heater in order to be heard properly by my fellow zoomers. The amplitude and frequency of my own voice does not layer well over the heater - it is either the heater or me; its hum is a quite dominant element of the otherwise-quiet environment of this little space.
My warm companion’s hum makes me ponder my regular walks in wilder places. Sherbrooke Forest springs first to mind - beautiful earth tracks meandering deep into this gorgeous pocket of damp forest. Humus: richly coloured and strongly fragrant from being recently turned by the scratchings of the Superb (and it is!) Lyrebird. Vivid greens erupt as a dynamic backdrop to my walks with Wurundjeri Country, with the seemingly limitless interdependencies with which I walk.
Yet, each time I walk into this verdant oasis and drop into the sensory wonder of being with the forest, I am struck by the sounds. As well as the abundant sounds of the forest which, to some extent, must be responding to my presence - and the smells, sounds, visions I bring - there is the ever-present sound of human settlements. The steady drone of cars on (apparently) nearby roads, chainsaws and chippers screaming to digest the hard wood of the Mountain Ash that towered (precipitously?) over new- and old-dwellings, the deep throb of a road bike thrilling through the bends of perfect camber, dogs barking, children crying, planes and helicopters rumbling across the sky, car doors slamming, air brakes sharing testimony of the steep terrain beyond this forest. The more deeply I listen, the more I hear: layers and layers of the human soundscape. It hits me: in order to interact and maintain its interdependencies, this forest must have to compete with the human hum which occupies so many frequencies, must adapt and expend energy to find space for communication within a crowded soundscape. Or…perish? What effect might this human hum have on the distribution of animals in the forest or on their ability to communicate, hear the footfalls or breathing of predator or prey, find a mate, find their small offspring…?
For decades, bioacoustic experts have recorded the natural ambient sounds of vocalising animals, including birds, amphibians (especially frogs), animals, insects and reptiles. Such sound recordings have yielded incredible spectrographs of natural soundscapes that reveal that each vocalising organism occupies its own niche, an ‘acoustic territory’ which provides that organism with the best opportunity to be heard. However, the research speaks volumes: the human soundscape is crowding the acoustic real estate and this is impacting on ecosystems (Tennesen 2008).
Bernie Krause, a world-leading bioacoustics expert who has studied soundscapes across the world for decades, once reported at least 40% of those natural soundscapes have been so radically impacted by the human soundscape (‘anthropophony’) that many species must be locally extinct. Indeed, sites with an ‘unpolluted’ soundscape are getting harder to find. Bernie’s work is incredible - a simple search on his name will yield fascinating insights into his work and findings. I encourage you to dive deeper…once you’ve watched Bernie’s TED Talk from 2013…
Staff from the US National Park Service have observed the anthropophony elicit changes in animals’ foraging behaviour, distribution and movement across the landscape, and reproductive effort and success. These changes could be cataclysmic for threatened species - I’m thinking of the Critically Endangered Helmeted Honeyeater Lichenostomus melanops cassidix (a swamp/riparian-dependent bird) as I write this. Their distribution and movement is tightly constrained by incredibly limited habitat, now mere vestiges in a floodplain landscape made otherwise uninhabitable by systematic draining of swamps, changed hydrology, and historic and current vegetation removal for agriculture and human housing. With nowhere else to move, when the human soundscape gets louder and the acoustic territories are occupied by the many frequencies of the anthropophony…how can their breeding calls be heard? And if they are heard, will the prospective mate be a neighbour - with the call not heard further afield - and what impact might this have on already bottle-knecked gene flow? Can their aerial predators, namely Goshawks, be heard over the human din? Conversely, can the Goshawk make out the almost indiscernible calls of a nestling - a valuable food source for a healthy top order - amongst the leaf blowers and two-stroke engines? What do we know of the impacts of the anthropophony on threatened species recovery efforts?
Is the acoustic territory of the Critically Endangered Helmeted Honeyeater also critically endangered? (Photo credit: Stephen Garth)
As an ecologist with a great interest in biodiversity planning, I wonder so many things, including: what do we know of the potential new soundscape that would accompany proposed land use and development applications? Diechmann et al. (2016) considered the impacts of the soundscape of natural gas exploration on biodiversity and found the sounds associated with construction and operation exerted some influence over the surrounding rainforest dynamics. Their findings prompted them to state:
“‘While acoustic monitoring has already been declared a Best Practice in monitoring biodiversity during and after oil and gas operations in marine habitats (ref. supplied), we recommend that it also be implemented as a best practice in the terrestrial realm...soundscape monitoring specifically should be implemented as part of government-required Environmental Impact Assessments and monitoring plans to improve their usefulness and efficacy.’”
A recent study in subtropical woodland in Australia considered how soundscapes may indicate effects of environmental and climatic factors (including climate change) on birds and insects (Scarpelli et al. 2023). Their findings also compelled the authors, with the paper stating: ‘it is highly recommended that monitoring schemes and impact assessments account for phenological changes and environmental variability [via soundscapes], as these are complex and important processes shaping animal communities’.
And what of freeway widening projects? Regulators installed in river systems? Acoustic repellent systems such as automated ‘gunshots’ to manage wildlife interactions with crops? Our soundscape is many, varied and occupies many frequencies. What species might also rely on space in these frequencies for their survival? What species are going extinct because they cannot find a free channel in the soundscape?
I’m back in the forest. The lyrebird that had been so active in turning the soil has found a mate; the male is producing such an incredible cacophony my ears are ringing. Layers and layers of overlapping and intermingled bird calls - a complex medley like an orchestra of different bird species simultaneously erupting from the male. The research into the complexity of the male lyrebird call is absolutely astonishing, with researchers discovering the males, during courtship and copulation, produce a ‘remarkably accurate acoustic illusion of a flock of mobbing birds’ (e.g. Dalziell et al. 2021). I marvel and wonder at the amplitude and frequency of sounds this one male is producing in a vertical soundscape - sounds all being produced at once - and consider this in the context of the anthropophony. I wonder if this acoustic feat has anything to do with adaptation to an ever-filling soundscape occupied by so many human sounds just beyond the forest’s edge, or whether the ability to occupy so many acoustic territories simultaneously might be a useful way to survive…within the sound of…humans.
The courting male Lyrebird produces an incredible and remarkably accurate acoustic illusion of a flock of mobbing birds - a soundscape all its own! (Photo credit: Alex Maisey)
References:
Dalziell, A.H., Maisey, A.C., Magrath, R.D. and Welbergen, J.A. (2021). Male lyrebirds create a complex acoustic illusion of a mobbing flock during courtship and copulation. Current Biology 31, 1970-1976.
Deichmann, J.L., Hernandez-Serna, A., Delgado C., J.A., Campos-Cerqueira, M. and Aide, T.M. (2016). Soundscape analysis and acoustic monitoring document impacts of natural gas exploration on biodiversity in a tropical forest. Ecological Indicators. 74, 39-48.
Scarpelli, M.D.A., Roe, P., Tucker, D. and Fuller, S. (2023). Soundscape phenology: the effect of environmental and climatic factors on birds and insects in a subtropical woodland. Science of the Total Environment. 878 (163080).
Tennesen, M. (2008). Gauging biodiversity by listening to forest sounds - noise from human activity threatens an animal’s reproductive success. Scientific American. October 1st, 2008.