International Journal of Molecular Zoology 2024, Vol.14, No.2, 111-127 http://animalscipublisher.com/index.php/ijmz 117 Magnetoreception mechanisms are hypothesized to involve magnetically sensitive proteins called cryptochromes, located in the retina, which form magnetically sensitive chemical intermediates known as radical pairs when they absorb photons of light (Warrant, 2021). Additionally, some animals use the inclination or tilt of magnetic field lines as a component of their magnetic compass sense, which can help maintain migratory headings and even distinguish among different inclination angles to exploit inclination as a surrogate for latitude (Wynn et al., 2020; Taylor et al., 2021). Experiments have shown that magnetic map cues can elicit homeward orientation in species like sharks and pink salmon, suggesting that these animals use a magnetic map to derive positional information (Putman et al., 2020; Keller et al., 2021). The study found that sharks can distinguish different positional cues from the geomagnetic field to navigate. This discovery is significant for understanding shark migration behavior and population structure in the marine environment (Keller et al., 2021). However, the magnetic sense is often considered 'noisy' and less reliable than other cues, which may explain why animals do not rely exclusively on geomagnetic fields for navigation (Johnsen et al., 2020). 6.2 Celestial navigation Celestial navigation is another crucial orientation mechanism used by migratory species. The position of the sun during the day and the stars at night provide reliable directional cues. For instance, birds utilize the position of the sun in the sky and their internal circadian clocks to maintain a constant direction (Mouritsen, 2018). This solar compass mechanism requires birds to adjust their direction based on the time of day, and thanks to their internal clocks, they can do so accurately. Studies have shown that birds can adjust their flight path based on the sun's position during the day and maintain a stable direction during migration. For example, homing pigeons use the angle of the sun to calibrate their flight path during long-distance flights; even when encountering cloud cover or other environmental disturbances, they can rely on their internal biological clock to make corrections (Padget et al., 2018). This ability not only ensures that birds can complete their migratory tasks accurately but also demonstrates the optimization of navigational abilities through natural selection in the evolutionary process. At night, many migratory birds switch to using the stars for navigation. They can identify constellations and use them to determine their position and direction (Mouritsen, 2018). Experiments on nocturnal migratory birds have shown that they can determine direction using simulated night skies, demonstrating their reliance on celestial navigation. In the Northern Hemisphere, the North Star (or Polaris) is particularly important because it provides a fixed reference point in the night sky. The constant position of Polaris makes it a reliable navigational marker, allowing migratory species to maintain the correct direction during long-distance migration (Tyagi and Bhardwaj, 2021). Research has found that some nocturnal migratory birds can remember the star patterns observed from their birthplace and use this memory during migration as adults, further enhancing their navigational accuracy. These findings not only deepen our understanding of animal migratory behavior but also provide scientific evidence for the conservation of migratory species. 6.3 Olfactory and visual cues Olfactory and visual cues also play important roles in navigation and orientation, particularly for species migrating through complex environments. Olfactory navigation involves using scent trails and environmental odors to locate specific places. For example, salmon (Salmo salar) use olfactory cues to navigate back to their natal streams for spawning. They imprint on the unique chemical characteristics of their home stream during early life stages and use this memory to guide themselves during their return migration (Ueda, 2018). Visual cues, such as landmarks and landscape features, are crucial for the navigation of birds and mammals. Birds often use visual landmarks like mountains, rivers, and coastlines to orient themselves during migration (Mouritsen, 2018; Zhang and Pan, 2021). Additionally, they utilize the patterns of polarized light, which change with the sun's position, to maintain their direction. Mammals, such as Connochaetes, rely on visual and olfactory cues to move along established migratory routes across the savannah in response to seasonal changes in vegetation and water sources (Curtin et al., 2018).
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