Communication and Signals - An Introduction to Behavioural Ecology - page 418

its way out? Secondly, if we are looking a stable equilibrium, what keeps deception at a
low enough frequency to prevent the system breaking down?

Fork-tailed drongos make deceptive alarm calls
A particularly impressive example of deception comes from Tom Flower's (2011)
work on alarm calls (Box 14.2) by fork-tailed drongos in the South African Kalahari
Desert. Fork-tailed drongos normally forage alone, catching insects on the wing,
or lizards and crickets on the ground. However, they sometimes follow other
species, such as cooperative groups of pied babblers or meerkats, catching food
flushed by these other species, or stealing food that has already been caught. This
stealing amounts to almost a quarter of the drongo's food intake and was achieved
in two ways, by either directly attacking or by taking food the forager had abandoned
after the drongos made a call from a nearby perch. Three sources of evidence
suggested that these calls from the perch were dishonest alarm calls, made to
make the forager flee from their food.

Fork-tailed
drongos steal
food from pied
babblers and
meerkats

BOX 14.2 ALARM CALLS
Animals often give alarms when they detect a predator (Zuberbühler, 2009;
Magrath et al ., 2010). These alarms may warn mates, offspring or other kin
(Chapter 11); they may attract others who join in mobbing the predator; or they
may signal to the predator 'I've seen you' and so dissuade an attack which
depends on surprise for success.
Different alarms are often given for different predators. For example, vervet
monkeys have different alarm calls for leopards, eagles and snakes. Playback
of the calls elicits different responses to each alarm, suited to the avoidance of
the different modes of attack of each predator: running into a tree after
leopard alarms; looking up and seeking shelter in a dense bush after eagle
alarms; and looking down at the surrounding ground after snake alarms
(Seyfarth et al ., 1980). Alarms may be varied, too, in response to the level
of urgency, becoming noisier or more rapid as the predator approaches
(Manser, 2001).
Amimals also often eavesdrop on the alarms of other species. For example,
vervet monkeys respond appropriately to both ground and aerial predator
alarms of superb starlings ( Spreo superbus ) (Seyfarth & Cheney, 1990). The
ability to eavesdrop on other species' alarms may sometimes arise because of
their acoustic similarity to conspecific alarms. However, learning is often likely
to be involved because species may respond to heterospecific alarms with very
different acoustic structure compared to their own alarms. Furthermore, they
do so only when familiar with heterospecific alarms, not when isolated from
them geographically (Magrath et al ., 2007, 2009).