Animals Stay Up At Night To Avoid Humans

It’s no secret that wildlife often avoid human contact – it’s a commonly observed and often documented behavior. Our presence can generate strong fear in wild animals, who in turn adjust their activity to minimize contact with us. Such risk avoidance can have important nonlethal effects on animal physiology and fitness. Our continuous expansion into wild territory has resulted in well-documented shifts in the spatial distribution of wildlife, but the potential effects on the temporal (time) dynamics of animals hasn’t yet been quantified.

In this study, a group of U.S. scientists put their heads together to examine anthropogenic effects on mammalian daily activity patterns, conducting a meta-analysis of 76 studies of 62 species from six continents. The reason behind it: fewer and fewer areas are available for animals to seek spatial refuge from people. So, researchers wanted to see whether — in places of wildlife and human cohabitation — animals minimize their exposure risk to humans by separating themselves in time rather than in space.

Risk ratios were calculated for each species and comparisons were made between the percentage of nighttime activity that occurred at sites during seasons of high human disturbance and during low-disturbance periods. The analysis spanned a wide range of human disturbances associated with diverse stimuli and corresponding levels of risk to wildlife:

• lethal activities – hunting and retaliatory persecution;
• nonlethal activities – hiking and natural resource extraction;
• human infrastructure – urban development, road construction, and agriculture.

The researchers found a significant increase in nocturnal activity due to anthropogenic activity. Mammal nocturnality increased by a factor of 1.36 in areas or time periods of high human disturbance relative to low-disturbance conditions, and 83% of all studied cases corresponded to a human-driven increase in nocturnality.

What’s more, there were increases in nighttime activity in response to all forms of human presence, suggesting that the findings are robust. Surprisingly, nonlethal activities generated very similar shifts in wildlife patterns to those from lethal activities. This indicates that wildlife perceive and respond to humans as threats even when we pose a nonlethal risk.

So, it seems that the behavior of animals in a human-altered world is quite flexible, and that has great implications for ecology and conservation. Temporal alterations in wildlife behavior may facilitate human-wildlife coexistence and effectively increase available habitats for species that are able to adjust. Species that are not able to adjust, however, are left in the lurch. Either way, inadvertently or not, humans may be imposing substantial costs on individual animals, where costly antipredator behavior may force compromises in reproduction and survival.

For their part, the researchers warn that an increase in nocturnality may eventually alter evolution through selection for adaptations better suited for nighttime activity. Keeping both the positives and negatives in mind, very few studies have examined the actual individual, population, and community-level consequences of these behavioral changes.

Wildlife advocates will be pleased to know that there are potential strategies that can mitigate these effects, and they are not out of the realm of possibility. One suggestion is “diurnal temporal zoning.” Identical to often-implemented spatial zoning, this strategy would restrict human activities during times of the day when species of conservation concern are most active or when the chances for negative encounters are highest. This, among other strategies, could help to ameliorate animals’ quality of life in the daytime so that they don’t need to seek a better life during the nighttime.