Fear of predators among wildlife can reduce a species’ population by half in five years

By Stephen Beech via SWNS

Fear of predators among birds and animals living in the wild can reduce the population of a species by half in less than five years, according to new research.

Predators killing prey takes a toll, but the study shows that fear - avoiding being killed - can itself devastate the population by so impairing parental investment and care fewer than half as many young reach adulthood.

And those that do are permanently handicapped as a result, say scientists.

Professor Liana Zanette and her team showed for the first time in any free-living wild animal that the fear predators inspire can itself reduce prey population growth rates.

The research team say their findings, published in the journal Proceedings of the National Academy of Sciences, conclusively establish that focusing solely on the number of prey predators directly kill and failing to additionally consider fear, as conventionally done, risks "dramatically underestimating" the total impact predators have on prey population size.

Wildlife ecologist Professor Zanette, of Western University in Canada, said: “These results have critically important implications for conservation, wildlife management and public policy.

“The total ecosystem benefits gained from conserving or rewilding native predators, and the full devastation wrought by introduced predators, must all now be re-evaluated.”

The researchers tested the impact of fear itself on the population growth rate over multiple generations in free-living wild song sparrows.

Fear was manipulated over three annual breeding seasons using playbacks of predator or non-predator vocalizations and the effects on births and survival were comprehensively quantified throughout each year, together with evidence indicative of impacts on births and survival beyond the parental generation.

Prof Zanette said: "Watching for predators kept parents from finding food for themselves and their young.

"This had cumulative, compounding adverse consequences, from fewer young being born, to fewer surviving each stage towards adulthood, and extending to those reaching adulthood showing evidence of impaired brain development likely to shorten their survival during adulthood – representing a transgenerational impact reducing population growth over generations."

She added: “Fear effects on prey population growth rates are likely the norm in birds and mammals because parental care is a fundamental characteristic of most birds and all mammals and fear‑induced reductions in parental investment and care are commonplace.

“Having now demonstrated that fear itself can contribute significantly to the total impact predators have on prey populations, we expect this will be found to be true in most ecosystems.”