Migration in Birds: Adaptations, reasons, and types of migration
Introduction: Migration in birds is a phenomenon in which birds travel from one place to another in search of favourable conditions and more resources for their survival. The migration also involves the journey to return to the original place.
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- The migration in birds takes place during seasonal change or movement between breeding or non-breeding location.
- The birds cover long distances in order to reach their destination during the migration journey, it is a difficult process, as they need more food, high energy, water, etc. to fly for a long time. Some migration journey becomes successful but some birds die due to the difficulties in the long route.
Historically, migration has been recorded as much as 3,000 years ago by Ancient Greek authors including Homer and Aristotle, and in the Book of Job, for species such as storks, turtle doves, and swallows.
Adaptation in migratory birds:
The birds who migrate from one habitat to another location for several causes like breed, feeding, and raising their offspring, are called migratory birds. These birds migrate from unfavorable location to location which possesses suitable conditions along with sufficient food and water resources and is also safe.
Migratory birds consist of good morphology as well as physiology as they cover long distances by flying, and also absorb other things.
- Birds need to alter their metabolism to meet the demands of migration. The storage of energy through the accumulation of fat and the control of sleep in nocturnal migrants require special physiological adaptations.
- In migrant birds, the feathers suffer from wear and tear and require to be molted. It gets moult usually once a year but sometimes twice. Moulting varies with some species prior to moving to their winter ground and others molting prior to returning to their breeding grounds.
Apart from physiological adaptation, sometimes behavioral changes also take place. Such as flying in flocks to reduce the energy used in migration or risk of predation. The time varies for different migratory birds but most of them prefer to fly at night as flying at night is much safe because the fear of predation is less in the night and they can fly and take rest easily at night because the air is cool in the night.
Reason for migration in birds:
The birds migrate for various reasons, some of which are as follows:
- The birds migrate for the need for food, most birds migrate from one place to another where adequate food can be obtained. So, the primary motivation for migration appears to be food; for example, some hummingbirds choose not to migrate if fed through the winter.
- The majority of birds usually migrate during the breeding season and sometimes for food resources or due to seasonal changes.
- They migrate also for healthy breeding. Birds migrate during the breeding season because they need healthy conditions such as a source of food, weather, adequate shelter, breeding colonies, safe places, etc. to raise their offspring.
- They migrate also because of changes in climatic conditions. As it is difficult to survive in harsh conditions like extreme cold or extremely hot, so the birds migrate to places of suitable climate conditions.
- The birds also migrate to save their offspring and themselves from predators and diseases.
General patterns of migration in birds:
Migration in birds is a regular seasonal movement. often north and south, undertaken by many species of birds.
Bird movements include those made in response to changes in food availability, habitat, or weather. Sometimes, journeys are not termed “true migration” because they are irregular (nomadism, invasions, irruptions) or in only one direction (dispersal, movement of young away from natal area).
- Approximately 1,800 of the world’s 10,000 bird species are long-distance migrants, many bird populations migrate long distances along a flyway.
- The most common pattern involves flying north in the spring to breed in the temperate or Arctic summer and returning in the autumn to wintering grounds in warmer regions to the south
- Within a species all populations may not be migratory, this is known as “partial migration”. Partial migration is very common in the southern continents; in Australia, 44% of non-passerine birds and 32% of passerine species are partially migratory
Timing/Behaviour of migration in birds:
In nocturnal migration, many birds give nocturnal flight calls. The migrants likely serve to maintain the composition of a migrating flock, and can sometimes encode the sex of a migrating individual, and avoid collision in the air.
Some important features of Nocturnal migrants:
- The nocturnal migratory birds land in the morning.
- The nocturnal migrant birds may feed for a few days before resuming their migration.
- These birds are referred to as passage migrants in the regions where they occur for a short period between the origin and destination.
- The nocturnal migrant minimizes depredation, avoids overheating, and can feed during the day.
- These birds cost the of nocturnal migration is loss of sleep.
- These migrants may be able to alter their quality of sleep to compensate for the loss.
Diurnal migrants fly mainly in the daytime such as crows, swallows, robins, blackbirds, hawks, cranes, jays, pelicans, geese, loons, shore birds, etc.
Important features of diurnal migrants:
- These birds migrate in the daytime. Migratory species in these groups have great difficulty crossing large bodies of water since thermals only form over land, and these birds cannot maintain active flight for long distances.
- The migrants may stop to forage in suitable places.
- They swallow and swifts capturing their insect food in the air as they travel.
- The diurnal migratory birds usually travel in flocks, which may be more or less organized.
Types of migration in Birds:
The main types of migration in birds are:
- Latitudinal migration
- Longitudinal migration
- Altitudinal migration
- Partial migration
- Erratic migration
- Seasonal migration
Latitudinal migration means the movement from north to south and vice versa. The birds live in the northern temperate and subarctic zones where they get facilities for nesting and feeding during summer. But during winter these birds move towards the south for shelter because the northern hemisphere becomes covered with snow and ice.
- Several birds of North America and Eurasia cross the equator and spend winter in deeper and warmer parts of South America and Africa.
- For example, the American golden plover passes the months of winter in the plains of Argentina. Ruff breeds in Siberia, and travels to Great Britain, Africa, and the plains of India and Sri Lanka, by traveling a distance of 6,000 miles.
It is an east-west and vice-versa migration of birds. It can be seen in the Patagonian plover, the birds visit the Falkland Island and South Patagonian in September and October for breeding.
In Altitudinal migration or vertical migration, the birds migrate from high mountains in the summer to low valleys. This type of migration occurs in many Indian and foreign mountaineer birds. It is common in mountains worldwide such as Himalayas and Andes.
- Several species of birds in India migrate during summer from planes to the slopes of the Himalayas and return to planes at the commencement of winter. An example of such a migrant is a common wood-cock.
- Dusky grouse in Colorado migrate less than a kilometer away from their summer grounds to winter sites which may be about 400 m in altitude than the summer site.
Within a species all populations may not be migratory, this is known as “partial migration”. Partial migration is very common in the southern continents; in Australia, 44% of non-passerine birds and 32% of passerine species are partially migratory.
- The song thrush, redbreast, titmouse, finch, etc are partial migrant birds.
In some species of birds erratic, vagrant, irregular, or wandering migration occurs. In these species of birds, after breeding, the adults and young move away from their homes to disperse in all directions in search of food and safety from enemies.
- These migrants sometimes die due to exhaustion or unknown shore. e.g. of some birds of these species, great blue heron, cuckoos, thrushes, and warbles.
According to some ornithologists, some birds migrate in a particular season. Seasonal migration is regular migration seen in birds according to season.
- For example – Swift, swallows, nightingales, and cuckoos are summer visitors in Britain, as they arrive in spring from the south, stay there to breed, and leave for the south in autumn.
- Some birds such as Sandpipers and Snipes were seen for short time twice a year on their way to colder or warmer countries in spring and autumn.
Threats and conservation of migratory birds:
Human activities threaten many migratory bird species. As some birds migrate from different countries to others, where they cross the political boundaries of countries, conservation measures require international cooperation.
|For the conservation of migratory birds, several international treaties have been signed to protect migratory species. Some international treaties for the conservation of migrant birds are “the Migratory Bird Treaty Act of 1918 of the US and the African Eurasian Migratory waterbird Agreement.|
Hunting along migration routes threatens some bird species.
- The population of Siberian cranes (Leucogeranus leucogeranus) which used to come in the winter season in India, declined due to hunting along the route, particularly in Afghanistan and Central Asia.
Other migratory hazards include pollution, storms, wildfires, and habitat destruction along migration routes.
- In the East Asian – Australian flyway, up to 65% of key intertidal habitat at the yellow Sea migration bottleneck has been destroyed since the 1950s.
- Many stopover sites have been destroyed or reduced due to human agricultural developments, these factors leading to an increased risk of bird extinction.
You can also read:
- Flight or Aerial Adaptation in Birds
- Characters of Archaeopteryx
- Pigeon (Columba Livia) – General Characters
- Phylum Chordata – Characteristics and Classification
- Scoliodon – Dogfish, Classification, and Characteristics
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