Background (5400)
Animal migration is a widely reported biological phenomenon, thought to
emerge due to seasonality in resource abundance (1). Found in all the
major branches of the animal kingdom, how individuals find their way to
and from these wintering grounds has fascinated scientists for
centuries. Until recently, our understanding of migratory routes was
limited to observations of species during migration, but developments in
biologging technology have revolutionised our understanding of both
migration routes and where animals spend their non-breeding period (e.g.
,2–4). While such technology has helped us understand the extent of
migratory movements and the importance of novel wintering areas, these
data also have the potential to help us understand how individuals
navigate over global scales to reach these destinations.
The mechanisms by which animals find their way between breeding and
non-breeding sites are still widely debated. Path integration, whereby
animals can assess their present location from past trajectories, was
first suggested by Darwin as a navigation system (5). Since then,
researchers have suggested that animals may use the sun, night sky (6)
or magnetic compasses (7,8), and cognitive mechanisms such as route
following (using landmarks ,9) and a cognitive map (Learning ,10).
However, these mechanisms do not fully explain how animals can navigate
over long distances or return home from new places (11), which is a
particular conundrum for birds which have some of the longest migrations
in the animal kingdom. It has been suggested that odour cues may create
an olfactory map (12,13) and recent evidence suggests that birds may
even be able to detect infrasound waves (14).
What is Infrasound
what is it emitted through …….
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natural sources
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anthropogenic sources
While infrasound is often thought to be generated by physical processes,
there is evidence it is both created and used in nature. It is thought
to be emitted by animals during mating displays (15,16) and in
communication, particularly in species which require signals to travel
over large distances (17–19). Animals are also thought to respond to
infrasound, altering their behaviour, such as by increasing activity
(20), avoiding storms or adverse weather (21), orientation to currents
(22) and changes in navigation (14). The idea that infrasound may be
used by animals for navigation has mainly been supported by studies on
pigeons (14,23,24) and this work has raised a series of research
questions which have never been widely tested in nature. First, this
work provides both correlational and experimental evidence that pigeons
use infrasound to navigate (14), showing that by damaging the ear, birds
are no longer able to respond to these sounds (23). Second, this work
has suggested that variation in navigation annually and geographically
may be explained by seasonal and inter-annual variability in infrasound
propagation (24). These results have revealed a possible mechanism which
could explain how birds and other animal navigate, and yet a
comprehensive study across species has never been carried out. Here we
propose to test these hypotheses using the largest database of animal
tracking in the world, combined with new experimental work on movement
and physiology.
While not widely tested, infrasound may also be used in both navigation
and shorter distance movements, as a mechanism to detect weather
systems, particularly in birds (21). It has been shown that birds time
their migration to optimise weather conditions (25–27) and foraging
behaviour in general has been shown to be strongly affected by weather,
particularly wind (28,29). As such the ability to detect the weather
from a distance would be highly advantageous, given to frequent cost of
extreme weather events (30) and the importance of optimal wind use
(31,32). Furthermore, some species, olfactory cues are thought to be
highly important and their plume dynamics are directly affected by wind
(33,34). As such, the evolutionary payoff to infrasound detection would
be huge in birds, particularly when other navigation mechanisms are not
possible.
Seabirds have the longest migrations of any species (Figure 1a ,2),
travelling from the north to south pole (35) and circumnavigating the
global multiple times (Figure 1b ,36). Moreover, seabirds are unlikely
to use visual landmarks to navigate as most species navigate across the
oceans away from land masses. Even trips to sea within breeding seasons
can result in trips of over 10,000km (37). Perhaps because of these vast
movements, seabirds have been the model species for biologging studies
(38,39). As a result, the global seabird tracking database contains 5
million data points from 104 species, covering all major seabird species
groups (Figure 1c). Seabirds use the seemingly featureless ocean for
short foraging trips during breeding and long distance migrations,
offering an opportunity to test the use of infrasound across a range of
spatial scales. Furthermore, natural differences in life history and
movement will allow comparative analysis between groups of species with
different movement patterns. Specifically this project will investigate
whether seabirds use infrasound in short and long distance navigation
and as a mechanism to detect both advantageous weather and extreme
conditions to be avoided.