In celebration of International Migratory Bird Day, we explore the incredible journeys of Tsavo’s migratory birds—how they find their way, why they travel, and how places like Tsavo provide critical stopovers and breeding grounds along their routes.
Why Do Birds Migrate?
Birds migrate to access abundant food, optimal breeding conditions, and favourable climates. Seasonal changes in day length and temperature trigger hormonal shifts, causing many species to undergo physiological transformations—such as fat accumulation and heightened activity—known as Zugunruhe (German for “migratory restlessness”). Even birds raised in captivity, with no exposure to natural seasonal cues, show this instinctual behaviour, indicating an internal circannual clock. Many birds will then form large flocks and migrate together, a behaviour that offers several advantages, including protection from predators and increased efficiency in navigation and finding food.
How Do Birds Navigate?
Birds use an astonishing array of tools to navigate during migration:
- Magnetoreception: Built-in magnetic field detection helps them follow the Earth’s magnetic lines.
- Sun and stars: Some species use celestial navigation to orient themselves.
- Visual and olfactory landmarks: Birds can use familiar landmarks like rivers, coastlines, and mountains to navigate. Some birds may also have a sense of smell that allows them to identify specific locations or follow scent gradients.
- Wind patterns: Birds can use wind to their advantage, migrating when favourable wind conditions are present.
- Social navigation: Birds may follow other birds, particularly younger birds learning the migration route, as a way to navigate.
- Internal clock: Birds have a circannual time program, a genetically determined internal clock, that regulates when to migrate and other behaviours throughout the year.
In essence, birds are incredibly skilled navigators, utilising a multi-sensory, innate toolkit to traverse thousands of kilometres.
Early Theories on Migration
Before the concept of migration was understood, ancient explanations for disappearing birds were quite imaginative. Some believed that birds hibernated in riverbeds or transformed into other species for the winter. The truth, uncovered through centuries of observation and science, is far more extraordinary.
Migration Isn’t Just for Flyers
Migration isn’t exclusive to airborne species. For example:
- Penguins, including several species of Spheniscidae, migrate by swimming, often travelling over 1,000 kilometres.
- Dusky grouse (Dendragapus obscurus) migrate altitudinally—primarily by walking.
- Emus (Dromaius novaehollandiae) in Australia have been known to move long distances on foot during drought conditions.
Different Types of Migrants in Tsavo
Tsavo sees a mix of migratory patterns:
- Palaearctic migrants: Species like the steppe eagle and barn swallow arrive from Europe and Asia to overwinter.
- Intra-African migrants: Birds such as the African paradise flycatcher move within the continent following rain and food availability.
- Altitudinal migrants: Some sunbirds and weavers travel between lowlands and highlands rather than crossing continents.
Key Migratory Birds Seen in Tsavo:
- Steppe eagle (Aquila nipalensis): Winters in East Africa after breeding in Central Asia.
- White stork (Ciconia ciconia): Migrates from Europe, passing through Tsavo en route to southern Africa.
- Barn swallow (Hirundo rustica): Breeds in Europe and winters in Kenya.
- Great white pelican (Pelecanus onocrotalus): Moves between inland lakes such as Lake Nakuru and Lake Elementaita and feeding areas like the Tsavo River.
- Yellow wagtail (Motacilla flava): Winters in East Africa after migrating from Europe.
- African paradise flycatcher (Terpsiphone viridis): Makes seasonal movements within Africa, often seen in Tsavo’s riparian zones.
These birds stop in Tsavo for rest, food, and safety on their long journeys. The best times to observe migratory species in Tsavo are between September and April, when most Palaearctic migrants are present.
The Longest Migrations on Earth
Bird migrations vary widely in distance and duration:
- Arctic terns travel over 70,000 km each year between Arctic breeding grounds and Antarctic waters—the longest known migration in the animal kingdom.
- Bar-tailed godwits fly non-stop over 13,000 km from Alaska to New Zealand.
Though pelicans may not break such records, their collective flights across Africa’s wetlands are no less impressive.
Why Tsavo Matters for Migrants
Tsavo is a lifeline for migratory birds. Its rivers and grasslands offer critical feeding and resting points.
While many of Tsavo’s migratory visitors pass through on their way to or from breeding grounds, some return year after year—testament to the importance of safeguarding these landscapes.