Why prey animals often see threats where there are none-and how it costs them

Why prey animals often see threats where
there are none—and how it costs them

March 2 2023, by Leah Gray and Mike Webster

Credit: AI-generated image (disclaimer)

For a nervous horror fan, an evening watching HBO's hit post-
apocalyptic television show The Last of Us might be followed by a
restless night under the duvet. The silhouette of a coat slung over the
back of a chair or even the screeching of a cat in the garden will cause a
spike of adrenaline.

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Animals are primed to be wary through natural selection rather than
scary television shows, but like humans, they often make mistakes when
watching out for threats.

Identifying stealthy predators is already a difficult task. From the
perspective of a songbird, a harmless crow flying overhead may look
similar to a raptor. But predator identification is made more challenging
by the fact that prey animals often juggle multiple activities like
foraging, keeping an eye on competitors and courting mates, all at the
same time.

This can be made easier by working as a group. Members of a school of
fish, flock of birds or herd of antelope can share the task of watching out
for predators. When an animal detects a predator, they share this
information with other group members directly, by producing a warning,
or inadvertently, by preparing to flee. The group as whole can then
respond by fleeing, hiding or adopting a defensive position.

But this information is not always reliable. Over half of the anti-predator
responses of greylag geese flocks occur when no predator is nearby.

The false alarm rate for South America's Guianan cock-of-the-rock
birds exceeds 70%. And more than three quarters of the responses of
semipalmated sandpipers and willow tits arise due to the
misidentification of harmless stimuli as predators.

These mistakes can be costly in terms of lost foraging and resting time
and wasted energy. But what causes these false alarms and how can
animals avoid them?

The likelihood of a false alarm

In a recent article, we reviewed research on predator misidentification

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and found that false alarms are common throughout the animal kingdom.
We found that the propensity for animals to produce false alarms varies
depending on three main factors:

      1. how clear the predator cues are

      2. the vulnerability of prey to predation

      3. the cost of performing alarm or escape behavior.

When predators are harder to identify, perhaps because they are well
camouflaged, an animal may be more likely to mistake unrelated sounds
or movements for a predator. Research found that bumblebees were
more likely to produce false alarms having previously been exposed to
highly camouflaged goldenrod crab spiders than bees that were
unaccustomed to them.

Some species are instead simply more vulnerable to predators than
others. This can be because they are not fast enough to escape a close
encounter or not equipped to fight a predator off. For these species,
ignoring a true alarm is more likely to result in death, so it may be
beneficial to follow a "better-safe-than-sorry" principle and pay the cost
of being occasionally wrong.

Willow tits produce alarm calls in response to most large aerial objects
including planes and crows. This is because they are typically hunted in
ambush attacks in which they are unlikely to escape. So the costs of
alarm calling at a few planes becomes dwarfed by the threat of being
killed in an attack.

In some circumstances, the cost of fleeing unnecessarily is higher and an
animal may require more certainty about the risk posed by a potential

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threat before taking evasive action.

Semipalmated sandpipers can double their body mass during staging
(where birds stock up on resources before migrating), which means that
flight will require substantially more energy. False alarms were found to
be less common later in staging when body mass was higher and escape
flights were more costly.

Who should be trusted?

False alarms raise a dilemma for animals that live in groups.

If they respond to potential threats too often, they waste energy and the
opportunity to perform other activities crucial to their survival. Greylag
geese, for example, lose 19 minutes of foraging time on average during a
false alarm. With multiple false alarms each day, this time adds up to a
substantial loss of food.

But if animals ignore ambiguous cues too often, they risk a true predator
attack and could be killed. Animals therefore employ a range of
strategies to prevent the spread of false information through their
groups.

In some species of rodent, corvid and primate, animals will remember
which individuals have been unreliable in the past and will stop
responding to their alarms.

In 1988, researchers played two different calls made by the same
unreliable signaller to a group of vervet monkeys. The monkeys, who
had learned to ignore one type of call made by the unreliable signaller,
also ignored an acoustically different call made by the same individual.

Many species also use a strategy called consensus decision making. If

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only one group mate raises an alarm, it is more likely to be false than if
                                   multiple members raise the same alarm. In this case, the group will take
                                   evasive action only if a certain number of group members respond to the
                                   information.

                                   Groups of common redshanks, a wading bird found in the UK and
                                   Europe, will respond immediately if multiple birds produce an escape
                                   flight simultaneously. But when only a single bird makes an escape
                                   flight, other group members will first scan the environment to assess the
                                   validity of the alarm before acting.

                                   Responses to threats, real or imagined, have an impact on the survival of
                                   prey species. But the balancing act of separating true from false alarms
                                   clearly influences how animals weigh up and respond to information
                                   from their group mates.

                                   This article is republished from The Conversation under a Creative
                                   Commons license. Read the original article.

                                   Provided by The Conversation

                                   Citation: Why prey animals often see threats where there are none—and how it costs them (2023,
                                   March 2) retrieved 29 December 2023 from https://phys.org/news/2023-03-prey-animals-threats-
                                   noneand.html

                                   This document is subject to copyright. Apart from any fair dealing for the purpose of private
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