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Thursday, 11 December 2014

Juvenile Osprey Navigation during Trans-Oceanic Migration. PLoS ONE, December 2014

Juvenile Osprey Navigation during Trans-Oceanic Migration.

PLoS One. 2014;9(12):e114557
PMID: 25493430


Authors: Horton TW, Bierregaard RO, Zawar-Reza P, Holdaway RN, Sagar P

To compensate for drift, an animal migrating through air or sea must be able to navigate. Although some species of bird, fish, insect, mammal, and reptile are capable of drift compensation, our understanding of the spatial reference frame, and associated coordinate space, in which these navigational behaviors occur remains limited. Using high resolution satellite-monitored GPS track data, we show that juvenile ospreys (Pandion haliaetus) are capable of non-stop constant course movements over open ocean spanning distances in excess of 1500 km despite the perturbing effects of winds and the lack of obvious landmarks. These results are best explained by extreme navigational precision in an exogenous spatio-temporal reference frame, such as positional orientation relative to Earth's magnetic field and pacing relative to an exogenous mechanism of keeping time. Given the age (<1 year-old) of these birds and knowledge of their hatching site locations, we were able to transform Enhanced Magnetic Model coordinate locations such that the origin of the magnetic coordinate space corresponded with each bird's nest. Our analyses show that trans-oceanic juvenile osprey movements are consistent with bicoordinate positional orientation in transformed magnetic coordinate or geographic space. Through integration of movement and meteorological data, we propose a new theoretical framework, chord and clock navigation, capable of explaining the precise spatial orientation and temporal pacing performed by juvenile ospreys during their long-distance migrations over open ocean.

How do juvenile ospreys navigate during trans-oceanic migration? Although a complete answer to this question remains elusive, our research has provided several relevant findings. The demonstration that juvenile ospreys are capable of maintaining constant course movements across large expanses of open ocean, despite the perturbing effects of highly variable winds, demonstrates that these birds have a remarkable ability to locate themselves in space and gauge their rate of forward progress. We further demonstrate that juvenile osprey movement behaviors are not compatible with the bicoordinate geomagnetic field intensity-inclination orientation hypothesis due to the lack of spatial resolution in this representation of magnetic coordinate space in the western Atlantic Ocean basin. However, vertical plane and horizontal plane magnetic cues, defined in a transformed magnetic coordinate space relative to each bird's hatching site, provides sufficient spatial resolution for the highly individual movements we observe and is compatible with the observations of others that many animals respond to vertical plane magnetic field conditions.

By integrating high resolution animal tracking technology with sophisticated meteorological and magnetic models, we show that the trans-oceanic migrations of juvenile ospreys are best explained by a spatio-temporal system of navigation. The chord and clock navigational system we propose provides a new theoretical framework for the analysis and interpretation of animal movements in dynamic environments. This new perspective on one of biology's oldest questions provides an interdisciplinary framework for future research targeting the means by which animals navigate. There is growing consensus that solving the grand challenges of organismal biology requires integrated and interdisciplinary research approaches [16], [29], [34]. We hope that the integrated approach we apply here inspires further synergistic research involving scientists from a range of disciplines.

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