Predator scent makes deer protect young forests

Deer do not have to spot a predator before becoming uneasy. Fresh research from forests in south-eastern Germany indicates that the scent alone of large carnivores can alter deer behaviour – a change that may improve the chances of young trees surviving.

The research examined a straightforward proposition: deer that perceive nearby danger may spend less time feeding on saplings. In this experiment, the signal of “danger” came in a distinctly unglamorous form: predator urine and scat.

A scent experiment in German forests

Scientists at the University of Freiburg created experimental plots in woodland areas where lynx and wolves have been reintroduced.

Across 11 locations, every site contained four plots, each assigned a separate scent: wolf, lynx, cow, or water as the control. Thirty planted saplings were placed in each plot.

The team repeatedly inspected the young trees for browsing damage. Camera traps were also used to record the behaviour of red deer and roe deer, including how frequently they appeared and the length of time they remained.

The overall result was unmistakable. Deer entered plots carrying predator scents less frequently and, when they did visit, spent less time there. Consequently, the saplings suffered less damage than those in the control plots.

Lynx scent had the stronger effect

A particularly notable finding was that the smell of lynx appeared to unsettle deer more than the scent of wolves.

The researchers suggest this may reflect the different way lynx hunt. As ambush predators, lynx stalk prey and attack at close quarters, meaning deer may interpret their scent as a more immediate threat – a sense that “you could be right here”.

Local history may also have played a part. Wolves were still becoming established in the study area, whereas deer had longer experience of living alongside lynx.

Put simply, deer may have had longer to “learn” that the smell of lynx can be followed by genuine danger.

Why predator scent matters for forests

Excessive browsing is a major issue across much of Europe. Large deer populations can damage young trees, delay forest regeneration, lower biodiversity and create costly losses for forestry.

Many common measures – including fencing, tree guards, culling and continual monitoring – require considerable labour and expense. The possibility that the presence of predators, or even signals of their presence, can change deer behaviour is therefore attractive: it points to a more natural, lower-intervention means of protecting regenerating woodland.

“At a time when debates around large carnivore conservation often focus on conflicts, our study highlights the benefits these species bring to landscapes,” said study co-author Walter Di Nicola.

“The presence of carnivores, even just their scent, could help reduce the ecological and economic problems associated with browsing from overabundant deer populations.”

Where large predators are absent

The researchers believe comparable effects may occur in countries such as the UK, despite wolves and lynx having been absent there for generations. Their reasoning is that deer retain an innate degree of caution towards predators, even if they have never encountered them.

However, they anticipate that the response may initially be less pronounced, becoming stronger if predators return and deer begin once more to learn what those scents signify.

“In the UK we would expect similar but probably weaker effects. Deer still have some innate fear of predators, even if those predators have been absent for generations,” Di Nicola said.
“Where predators return, we expect these responses – and their ecological benefits – to become stronger over time.”

A valuable finding, with an important caveat

The team is careful not to overstate the implications. Its experiment relied on concentrated scents positioned so that deer could readily detect them.

Conditions in nature are far less orderly. In the wild, signs of predators are uneven, dispersed and unpredictable, while real predator–prey relationships include movement, hunting pressure, changing deer groups, seasons and learning over time.

The experiment therefore does not completely reproduce what occurs when predators are living and hunting actively within an ecosystem.

Even so, it demonstrates an important point: deer react not only to pursuit or attack, but also to risk – even merely the suggestion of it – and that can by itself alter a forest’s future.

In essence, the study shows that large carnivores influence landscapes in ways beyond the simple idea that “predators eat prey.”

Carnivores can also change behaviour: where prey travel, how long they remain and what they are willing to eat. Those seemingly small decisions can then have wider effects on forest recovery.