International Journal of Molecular Zoology 2024, Vol.14, No.2, 111-127 http://animalscipublisher.com/index.php/ijmz 113 In addition to the important role of internal clocks, external cues such as light, temperature, and food availability also influence migratory patterns. These cues help synchronize internal rhythms with the external environment, ensuring successful migration (Bellastella et al., 2021). Understanding these rhythms and their mechanisms provides crucial insights into how animals adapt to their environments and optimize their survival strategies. 3 Environmental Cues and Migratory Timing 3.1 Photoperiod and seasonal changes Photoperiod, or the length of day, is a critical environmental cue that influences the timing of migration in many animal species. Birds, for instance, exhibit daily (circadian) and seasonal biological rhythms that are often synchronized with changes in day length. This synchronization helps them prepare for migration by inducing physiological and behavioral changes necessary for the journey. For example, in pine siskins, variation in chronotype, which is influenced by photoperiod, is associated with the timing of spring migration (Rittenhouse et al., 2019). Additionally, photoperiod-induced changes in behavior and physiology, such as body fattening and migratory restlessness, are crucial for the success of migration in Palearctic-Indian migratory buntings (Sharma et al., 2022). 3.2 Temperature and climatic factors Temperature is another significant environmental cue that affects migratory timing. Birds often use local temperature conditions to decide when to start their migration. For instance, Asian houbara (Chlamydotis macqueenii) use local temperature cues to time their spring migration departure, with individual birds showing consistent responses to temperature across multiple years (Burnside et al., 2021). Similarly, climatic factors such as temperature and precipitation play a crucial role in shaping the migratory strategies of bird species like the Eastern Kingbird (Tyrannus tyrannus) and Fork-tailed Flycatcher (Hemitriccus furcatus). These species track temperature and precipitation patterns to optimize their migratory routes and timing (MacPherson et al., 2018). Furthermore, changes in temperature due to climate change have been shown to influence the timing of migration in wading birds, with some species migrating later in response to rising temperatures (Mondain‐Monval et al., 2021). 3.3 Food availability and resource distribution Food availability and resource distribution are also key factors that influence migratory timing. Animals often time their migrations to coincide with periods of high resource availability to maximize their chances of survival and reproductive success. For example, spatial and temporal fluctuations in resource availability have led to the evolution of varied migration patterns in different species. Obligate migrants, which undertake regular annual migrations, often move between locations where resources are predictable and sufficient (Watts et al., 2018). Intraspecific variation in migratory destinations among North American bird species suggests that access to resources during the breeding season is a significant driver of migration (Bonnet‐Lebrun et al., 2020). Additionally, the availability of food resources during the non-breeding season, such as high precipitation areas that support abundant food, influences the migratory patterns of species like the Eastern Kingbird (Tyrannus tyrannus) and Fork-tailed Flycatcher (Hemitriccus furcatus) (MacPherson et al., 2018). Environmental cues such as photoperiod, temperature, and food availability play crucial roles in determining the timing of migration in animals. These cues help animals optimize their migratory strategies to ensure successful navigation and survival across different habitats and seasons. Understanding these cues and their interactions is essential for predicting how migratory species will respond to changing environmental conditions. 4 Genetic and Epigenetic Regulation of Migration 4.1 Genetic basis of migration Migration is a complex trait influenced by various genetic factors. Research indicates that migratory behaviors, such as timing and direction, are often under strong genetic control. Merlin and Liedvogel (2019) explored the genetics and epigenetics of animal migration and orientation, with a focus on the migratory behaviors of the European blackcap (Sylvia atricapilla) and the North American monarch butterflies (Danaus plexippus). Their studies revealed significant genetic differences in migratory behavior among species. For instance, the migratory
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