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 …….
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.