International Journal of Molecular Zoology 2024, Vol.14, No.2, 111-127 http://animalscipublisher.com/index.php/ijmz 116 Talal et al. (2023) discussed how high carbohydrate intake affects lipid storage and migratory flight capacity in locusts. The study found that locusts consuming high carbohydrates performed better in both total flight time and the longest single flight duration, with fewer pauses. These findings suggest that carbohydrates not only provide energy for migratory flights but may also extend flight time by reducing oxidative stress and minimizing water loss through various mechanisms. Similarly, migratory birds exhibit elevated levels of triglycerides and free fatty acids during migration, which are essential for meeting the high energy demands of flight (Sharma et al., 2022). 5.2 Muscle physiology and endurance Muscle physiology and endurance are also vital for migration. Migratory birds undergo significant changes in their flight muscles, including hypertrophy and increased aerobic capacity, to support sustained flight. For example, DeMoranville et al. (2019) studied the physiological changes in gray catbirds (Dumetella carolinensis) throughout their annual cycle, particularly during the pre-migratory preparation and migration periods. The study found that the metabolic rate of gray catbirds was highest during migration, with significant increases in the heart and flight muscles during pre-migration and migration periods. Additionally, the research revealed the importance of transcription factors such as PPARs and ERRs in regulating the metabolism of the flight muscles and heart of gray catbirds, especially in the utilization and storage of fatty acids during migration. These findings suggest that migratory birds adapt to different stages of their annual cycle through metabolic and muscle flexibility. Furthermore, the hypertrophy of flight muscles is accompanied by changes in heart mass and mitochondrial content, further supporting the high metabolic demands of migration (DeMoranville et al., 2019). In a study by Vernasco et al. (2021), it was found that the pectoral muscles of the nomadic migratory bird pine siskin (Spinus pinus) undergo significant changes during migration preparation, including hypertrophy and alterations in endocrine signaling components. These changes are crucial for regulating the entry into the migratory state and supporting the high energy demands of flight. Similarly, the light-bellied brent goose (Branta bernicla hrota) exhibits a strategic delay in migratory departure to enable the reorganization of its physiology into a flying phenotype, which includes the atrophy of non-essential organs and the growth of flight muscles (Handby et al., 2022). 5.3 Hormonal regulation Hormonal regulation plays a crucial role in mediating the physiological changes associated with migration. Changes in photoperiod and environmental cues trigger neuroendocrine responses that regulate the timing and progression of migration. For instance, migratory birds exhibit elevated levels of triiodothyronine and corticosterone, which are associated with increased fattening and migratory restlessness (Sharma et al., 2022). The expression of genes involved in thyroid hormone signaling and dopamine biosynthesis also changes in response to migratory cues, highlighting the importance of hormonal regulation in migration (Sharma et al., 2022). Studies have found that in the pine siskin (Spinus pinus), the expression of endocrine signaling components in the flight muscles changes during the transition into the migratory state. These changes indicate that the endocrine system plays a crucial role in regulating the physiological adaptations required for migration (Vernasco et al., 2021). Additionally, the regulation of appetite and fuel store set-points by neuroendocrine mechanisms is crucial for ensuring that migratory animals accumulate sufficient energy reserves for their journeys (Guglielmo, 2018). In summary, the physiological adaptations to migration involve complex interactions between energy metabolism, muscle physiology, and hormonal regulation. These adaptations enable migratory animals to optimize their energy use, enhance their endurance, and regulate the physiological changes necessary for successful migration. 6 Navigation and Orientation Mechanisms 6.1 Magnetic compass and geomagnetic fields Many migratory animals utilize Earth's magnetic field as a crucial navigational aid. This ability, known as magnetoreception, allows animals to detect the geomagnetic field and use it as a compass to determine their spatial orientation. Birds, sea turtles, fishes, crustaceans, and insects are among the diverse taxa that depend on this field for both short- and long-range navigation (Warrant, 2021).
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