The influence of human disturbance on wildlife nocturnality

Gaynor and collaborators (1) conducted recently a meta-analysis of 76 published studies, including 62 species from 6 continents, on the activity of medium and large-bodied mammals across gradients of human disturbance worldwide. Specifically they used as effect size (n=117) the ratio of the percentage of activity that occurs in the night in areas of high human disturbance over the percentage of nocturnality in areas of low human disturbance (Risk Ratio), measured on a logarithmic scale. They found an overall positive effect size of 36%. This means for example that if nocturnality has a value of 30% in low disturbance conditions, the value of nocturnality in high disturbance conditions increases to 41% as an average across study cases. The authors also conclude that temporal avoidance of humans may facilitate human-wildlife coexistence.
Although we acknowledge that the meta-analysis is sound we think there is an alternative interpretation of their results that passed unnoticed to the authors. Centuries-old historical persecution of mammals all over the world pushed them to spatial refuges and to a nocturnal life. Hence, the by-default state now for many mammal species worldwide is nocturnality. The fact that the authors found a number of cases (those included in the lower left corner of Figure 1b) reflecting that under low human disturbance conditions nocturnality is low (e.g. lower than 50%) is by itself quite an achievement. It means that all over the world (i.e. no statistical differences among continents were detected) when human disturbance is reduced wildlife becomes more diurnal (less nocturnal). We think this is one of the main messages to highlight from this paper.
Importantly, the authors did not try to assess whether mammals are showing a trend in time towards increased nocturnality. They simply had insufficient data to test a trend in time. However the way of discussing results was confusing at times, leading to possible misunderstandings. In fact press releases around the world have echoed that mammals are becoming (over time) increasingly nocturnal, although this is not the message the authors wanted to convey. At least in economically developed continents such as Europe we have found that wildlife is increasingly fearless of humans, live closer to villages and cities, recolonize habitats where they have been absent for centuries and are more diurnal due to lack of direct persecution (2). This trend has been going on during the last 60-70 years in Europe, in a non-linear way, and its effects are now becoming now evident. As countries develop economically rural life is abandoned and wildlife is not a competitor or an enemy anymore, and changed human attitudes allow the recovery of bold behaviours. Developing countries, where rural life is still dominant, will likely take longer to reach this stage. In Spain Eurasian otters (Lutra lutra) can be observed now at short distance, in all kinds of habitats, including highly urbanized ones, and also are now a common sight during the day, something that was unthinkable a few decades ago when otters were temporal refuges at night in the upper stretches of rivers because they were hunted for their fur. We recently studied otter foraging ecology in a reservoir located in NW Spain and were able to observe 655 hunting attempts by otters in two years’ time, all of them diurnal. Also from our own camera-trap data for a whole annual cycle in a mid-mountain site in NW Spain, where hunting is banned, we observed that roe deer (Capreolus capreolus) was mainly diurnal (63% diurnal pictures, 37% nocturnal; n=104). Even Iberian wolves (Canis lupus), still persecuted nowadays, can be observed during the day resting or hunting at short distance, just after 15 years of absence of direct persecution in protected sites.
We suggest that future human-wildlife coexistence worldwide will not be based on increased nocturnality but rather in the loss of fear of wildlife to harmless humans and on increased tolerance of humans to the close presence of wildlife. This will bring (is bringing) a new paradigm of human-wildlife coexistence that includes a greater ease to spot wildlife during the day, but also new challenges in our relationship with wildlife, such as increased attacks to humans, to human pets or to livestock or a higher frequency of road accidents. Temporal (or spatial) exclusion of wildlife cannot be called coexistence but rather avoidance. Data from the last few decades (a good part of them compiled in the meta-analysis) suggests that the trend towards the future may be one of increased temporal match with wildlife as the world becomes increasingly urbanized and people is more tolerant towards wildlife, rather than the opposite (3, 4, 5, 6, 7, 8, 9).

References cited
(1) K. M. Gaynor, C. E. Hojnowski, N. H. Carter, J. S. Brashares, The influence of human disturbance on wildlife nocturnality. Science 360, 1232-1235 (2018).
(2) A. Martínez-Abraín, J. Jiménez, D. Oro, Pax Romana: “refuge abandonment” and expansion of fearless behaviours in a reconciling world. Anim. Conserv. https://doi.org/10.1111/acv.12429 (2018).
(3) A. Martínez-Abraín, D. Oro, V. Ferrís, R. Belenguer, Is growing tourist activity affecting the distribution or number of breeding pairs of Eleonora’s Falcon? Anim. Biodiv. Conserv. 25, 47-51 (2002).
(4) A. Martínez-Abraín, J. Crespo, J. Jiménez, A. Pullin, G. Stewart, D Oro, Friend or foe: societal shifts from intense persecution to active conservation of top predators. Ardeola 55, 111-119 (2008a).
(5) A. Martínez-Abraín, D. Oro, D. Conesa, J. Jiménez, Compromise between seabird enjoyment and disturbance: the role of observed and observers. Environ. Conserv. 35: 104-108 (2008b).
(6) A. Martínez-Abraín, J. Crespo, J. Jiménez, J. A. Gómez, D. Oro, Is the historical war against wildlife over in Southern Europe? Anim. Conserv. 12: 204-208 (2009).
(7) A. Martínez-Abraín, D. Oro, J. Jiménez, G. Stewart, A. Pullin, A systematic review of the effects of recreational activities on nesting birds of prey. Basic Appl. Ecol. 11: 312-319 (2010).
(8) A. Martínez-Abraín, J. Crespo, M. Berdugo, L. Gutierrez, A. Lafuente, A. Mañas, J. M. de Miguel, Causes of human impact to protected vertebrate wildlife parallel long-term socio-economical changes in Spain. Anim. Conserv. 16: 286-294 (2013).
(9) A. Martínez-Abraín, J. Jiménez, Anthropogenic areas as incidental substitutes for original habitat. Conserv. Biol. 30: 593-598 (2016).