Deforestation is changing the way monkeys communicate in their natural habitat, according to a new study led by Laura Bolt, an adjunct professor in the Department of Anthropology. The research offers the first evidence in animal communication scholarship of differences in vocal behaviours in response to different types of forest edge areas, particularly areas changed by human activity.
Working in a tropical lowland rainforest in Costa Rica, the researchers examined how human-caused forest habitat changes have affected vegetation and, in turn, the rate and length of howling by the group-living howler monkey species.
The study compared how the communication behaviour of the mantled howler monkey differs in forest edges impacted by human activity, known as anthropogenic edges, compared to natural forest edges.
“Howler monkeys are well-known for making very loud, long-distance vocalizations called howls,” said Bolt. “While howls are only produced by adult males, howl function is not entirely known, so we conducted our study to test the hypothesis that the intensity of howling by monkeys relates to defending ecological resources such as areas of richer vegetation or preferred feeding trees.”
Anthropogenic areas were identified as areas within 50 meters of barbed wire fences marking the edge of the forest and the start of coconut plantations or cattle pasture, and natural forest edges as areas within 50 meters of a river.
The study found that males howl to defend high-quality resources, with notably longer durations of howling in the forest interior and at river edge areas where vegetation resources are richer. The researchers also found differences in howl length between river edge and anthropogenic edge areas, which is an important insight for conservation planning.
“Howler monkeys eat leaves and fruit, and if they are howling to defend these resources, we predicted that males would howl for longer durations of time when in a forest interior or near the river edge, where vegetation is richer compared to anthropogenic edge,” said Bolt.
To conduct their study, the researchers collected data on mantled howler monkey howling behaviour from May to August in 2017 and 2018, following groups as they travelled across various edge and interior habitat zones. All monkey groups were well-habituated and did not react to the visible presence of the researchers.
With their evidence showing that anthropogenic deforestation is altering howler monkey behaviour, Bolt and her colleagues say that long-term howler monkey conservation initiatives should prioritize preservation of forest interior and river edge regions and re-forestation of human-caused forest edges.
“While
it
is
yet
unknown
what
implications
these
behavioural
changes
across
different
edge
zones
may
have
for
monkey
fitness,”
says
Bolt,
“our
findings
show
that
it
is
proximity
to
anthropogenic
forest
edge,
rather
than
to
naturally-occurring
forest
edge,
that
is
changing
howler
monkey
communication
behaviour.
This
is
just
one
of
the
many
ways
that
howler
monkeys
are
affected
by
deforestation.”
Howling
by
the
river:
howler
monkey
(Alouatta
palliata)
communication
in
an
anthropogenically-altered
riparian
forest
in
Costa
Rica
is
co-authored
by
Bolt
with
Dorian
G.
Russell
(American
University),
Elizabeth
M.C.
Coggeshall
(Central
Washington
University),
Zachary
S.
Jacobson
(University
of
Calgary),
Carrie
Merrigan-Johnson
(University
of
Toronto
at
Mississauga),
and
Amy
L.
Schreier
(Regis
University).
The
study
will
be
published
in
the
journal
Behaviour
in
spring
2020.
This story is adapted from a University of Waterloo media release.