Every year, animals across the globe embark on incredible journeys, navigating thousands of miles to travel between their summer and winter homes. This mass movement of wildlife, called migration, is one of nature’s great spectacles. But how do animals know when it’s time to migrate?
What is migration?
Migration is the large-scale seasonal movement of animals from one area to another. This movement allows animals to find areas with favorable conditions and an abundance of resources during different times of the year. Some common reasons animals migrate include:
- Access to food – Moving to areas when food is seasonally abundant
- Access to water – Escaping droughts and finding ample water sources
- Breeding – Traveling to suitable areas to mate and give birth
- Avoiding harsh weather – Evading extreme cold or heat
Some well-known migrating species include wildebeests, monarch butterflies, humpback whales, caribou, and many species of birds. Migration distances vary widely among animals. While some migrations are relatively short – such as deer moving dozens of miles – other journeys can span thousands of miles across entire continents and oceans.
Migration cues
So what signals tell animals it’s time to migrate? Most migratory creatures rely on a combination of internal clocks and environmental cues. Here are some of the primary factors that spur the migration process:
Changing day length
As seasons change, the hours of daylight gradually lengthen and shorten. Many species are keenly aware of these subtle shifts in day length, which provide vital clues that it’s time to migrate. Even small variations of a few minutes trigger hormonal changes and prompt animals to start migrating. Day length serves as such a reliable indicator of seasonal progression that it’s the primary migration cue for many animals.
Temperature changes
Temperature changes also herald seasonal transitions. While day length provides an early warning, animals rely on temperature shifts at their location to fine tune migration timing. A stretch of warmer or colder than normal weather can accelerate or delay migrations.
Food availability
The supply of food is another signpost for migration. When food becomes scarce, it signals animals to move on. Likewise, when food becomes abundant in a new area, it can draw migrants to that location. Birds, in particular, travel huge distances between areas of peak food abundance. Moving from breeding areas to wintering grounds allows them to take advantage of seasonal peaks in their food supply.
Precipitation
Changes in rainfall patterns often prompt migration. The start of the rainy season in Africa, for example, spurs large herbivore migrations to track the new growth of vegetation. Meanwhile, a lack of rain and depleted water sources in dry areas stimulates migrations to places with adequate water.
Social cues
Some animal migrations are socially triggered. Species that migrate in herds, such as wildebeest, take their cues from the collective. When a few animals in the group begin migrating, this stimulates others to follow. Social compulsion helps keep the herd together and navigating in the right direction.
Internal rhythms
Beyond responding to external signals, many animals have an internal rhythm that guides migration timing. Even animals raised in constant conditions with no environmental cues will follow these innate rhythms and attempt to migrate at specific times. These intrinsic cycles ensure animals migrate at the optimal timeframe to take advantage of seasonal conditions.
Navigation abilities
Migrating across vast distances in the wild presents significant navigational challenges. Researchers have uncovered fascinating details about how different species accomplish these migratory feats.
Birds
Birds rely on a number of sophisticated navigational strategies during migration including:
- The sun – Using the sun’s position to orient direction
- Stars – Using star maps in the night sky for guidance
- Earth’s magnetic field – Detecting magnetic field lines to determine latitude and direction
- Visual landmarks – Using recognizable landscape features to guide the route
- Smell – Tracing airborne odors to locate stopover sites and final destinations
Insects
Insects like monarch butterflies use a combination of strategies including:
- Sun – Using daylight cues to orient direction
- Earth’s magnetic field – Detecting magnetic fields to maintain bearing
- Visual landmarks – Pinpointing landmarks to guide the route
Fish
Salmon and other fish rely mainly on their excellent memories to return to their place of birth to spawn. Young fish memorize the scents, water features, and magnetic field of their home river before going out to sea. When returning, these imprinted memories guide them back to the exact location years later to complete the migration cycle.
Sea turtles
Sea turtles have an inborn magnetic map they use to migrate huge distances. Hatchlings imprint on the magnetic field around their natal beaches. When it’s time to return and nest, adults use this magnetic map to guide themselves back after years roaming the oceans.
Threats to migrating animals
While migration gives animals access to better resources, these perilous journeys come with considerable risks. Here are some of the major threats migrating animals face:
- Habitat loss – Destruction of key breeding and feeding sites
- Barriers – Human infrastructure like roads and dams blocking routes
- Overhunting – Unsustainable harvests depleting populations
- Climate change – Shifting conditions disrupting delicate timings
- Pollution – Toxins accumulating in the body over long distances
Protecting migratory pathways and coordinating conservation efforts across borders and continents are key to preserving these species and their impressive migrations into the future.
Fascinating migration examples
Now let’s spotlight some incredible real-world migrations:
Arctic tern
The arctic tern flies an astonishing round-trip of over 40,000 miles each year – the longest migration of any animal. Terns breed in the Arctic during the summer, then travel to the Antarctic for the southern summer, riding alternating air currents between the two polar regions. Their route zigzags down continental coastlines, across oceans, and even through harsh tropical storm systems. Using this marathon migration, arctic terns experience more daylight hours in a year than any other creature.
Humpback whale
Humpback whales undertake one of the longest migrations of any mammal. Populations in the Northern Hemisphere travel up to 5,000 miles between their tropical breeding grounds and polar feeding areas. Their round trip can total 16,000 miles. Humpbacks navigate using underwater landmarks, magnetic fields, and celestial cues. Their exhausting journey is fueled by huge blubber reserves built up in feeding grounds.
Wildebeest
Each year, nearly 2 million wildebeest and other grazing animals migrate across the Serengeti in Tanzania and Kenya. This clockwise loop follows the seasonal rains to ensure lush grass for calves and plenty of water. Their 800-mile circuit is one of the last remaining large-scale migrations. Moving in enormous herds provides safety in numbers from predators like lions, hyenas, and crocodiles.
Ruby-throated hummingbird
Ruby-throats make a phenomenal overwater journey for a bird that weighs less than a nickel. They fly non-stop 500 miles across the Gulf of Mexico between North America and Central America. To power this grueling flight, they build up fat reserves equal to over half their tiny body weight.
Leatherback sea turtle
Leatherbacks are the longest migrating sea turtles. After nesting, leatherbacks travel over 10,000 miles into the Pacific Ocean all the way to the jellyfish-rich waters off South America. Then they swim all the way back to breeding beaches on the same exact stretch of coast. Leatherbacks can dive over 3,000 feet deep and average about 50 miles per day during these lengthy migrations.
Animal | One Way Distance | Total Distance |
---|---|---|
Arctic Tern | 20,000 miles | 40,000+ miles |
Humpback Whale | 5,000 miles | 16,000 miles |
Wildebeest | 800 miles | 800 mile circuit |
Ruby-throated Hummingbird | 500 miles | 500 miles |
Leatherback Sea Turtle | 5,000+ miles | 10,000+ miles |
Animal migration patterns
Not all migrations follow the same patterns. Here are some of the main types of migration movements:
- Latitudinal migration – The most common pattern where animals move between higher and lower latitudes seasonally, often between temperate and tropical zones.
- Altitudinal migration – Moving up and down mountain slopes to follow optimal conditions and resource availability.
- Longitudinal migration – Traveling east and west between regions rather than north and south.
- Nomadism – Wandering over large areas in irregular patterns to find resources.
- Irruption – Sporadic and unpredictable mass migrations triggered by sudden events like food shortages.
- Partial migration – Only some individuals or segments of a population migrate while others remain residents.
Research techniques
Scientists use a variety of innovative techniques to study the mysteries of animal migration, including:
Tagging
Attaching tags that transmit tracking data helps researchers follow migration routes and timing. Tags include numbered bands, wing tags, radio transmitters, and GPS satellite tags.
Stable isotope analysis
Examining ratios of elements like hydrogen and strontium in tissue or feathers can reveal where a migratory animal traveled from.
Genetic analyses
Analyzing DNA and genetic markers in populations can map the origins and paths of migrating animals.
Motus Wildlife Tracking System
A collaborative network of automated radio receiver stations across the Americas tracks tiny radio transmitters on migrating animals. This reveals detailed migration timing, speed, and paths.
Radar and aerial surveys
Radar data and aerial surveys provide big picture data on large-scale movement patterns and population numbers.
Citizen science
Observations from birdwatchers and other citizen scientists help piece together migration patterns and timing over broad geographic scales.
Evolutionary origins
So when and why did migration first evolve in animals? Migration likely emerged independently among early species of birds, mammals, fish, and insects seeking resources and habitat. Over time, natural selection favored mutations that improved navigation ability and timing. As populations grew, competition increased, spurring further migrations. Certain animals also genetically programmed migration into their instincts, ingraining it into the annual cycle.
While scientists debate certain details, they agree migration developed due to a combination of evolutionary drivers including:
- Searching for resources like food, water and shelter
- Avoiding predators, parasites and other dangers
- Finding suitable breeding locations
- Escaping harsh weather and climatic shifts
The appearance of migration so early in divergent branches of life on Earth highlights it as a highly successful and advantageous survival strategy. The phenomenon continues shaping the natural world today.
Conclusion
Animal migration is a captivating phenomenon driven by an intricate interplay of external cues, internal programming, and navigational wizardry honed by millions of years of evolution. These remarkable journeys are a testament to the determination, endurance, and ingenuity of animals across the globe. Gaining further insight into migration promises to reveal deeper mysteries into how Earth’s creatures thrive and move in synchrony with our dynamic planet.