What is migration?
Migration is when animals make a special journey to a more suitable environment usually twice a year because of food availability, breeding sites and bad weather. In Britain, when the weather gets colder and the days are shorter animals have a choice between hibernating or migrating to somewhere where food is still plentiful. Some birds are able to adapt and survive the cold weather here but others fly to warmer parts of the world because they are insect eaters and need to have a ready supply of food. In winter insects die or hibernate. Also the weather is just too cold for some of the young to survive. But why do birds leave warmer countries such as Africa to return again in spring to breed in Britain? After all, there is still plenty of food there. They come back to Britain because there are less predators and less competition for food and space to breed and raise their young. The days are longer in Britain during the summer months so there is more light to be able to find food to feed their young. In autumn we also get birds that migrate to Britain from Scandinavia and Russia because our weather is much milder and they have the food here that they need to survive.
Types of migration
There are three kinds of bird visitors that migrate to and from Britain.
Winter Visitors
Birds such as many of the ducks and geese, whooper swans, fieldfare and redwing fly to Britain from colder countries in the north such as Scandinavia and Russia because there is more food available here. Many of these countries have snow and ice for much if not all of the winter. They return north in the spring to breed.
Summer Visitors
Birds that come to Britain to breed here during the summer come from countries that are farther south such as Africa and Spain where it is warmer in winter. These include the birds such as swallow, house martin, swift, sand martin, cuckoo. In Autumn they return south with their young to here there is good source of food. Also birds that have spent the winter out at sea such as puffin and manx shearwater arrive on Britain's coastline to breed.
Passage migrants
These are birds that are either migrating north or south and stop in Britain to rest and feed. This is like us stopping at a Service Station on a motorway for a while during a long journey to eat and rest. These birds are usually seen in spring and autumn during their long journey either north or south.
How do birds know when to migrate?
In Britain it is the season changing. The days getting shorter and the weather getting colder and maybe getting harder to find food such as insects tells the birds it is time to leave. The winter migrants fly back north as the days start to get longer and the British weather starts to get milder.
How do they know the way?
So how do they know where to go? I think bird migration is fascinating. They don't have Sat Navs, maps or even a compass and yet even the young birds who have never migrated know where to go! There are four possible ways that birds navigate. One of the main ways is that is passed down through their genes from their ancestors and it is instinct that they know the route. Some birds use magnetic fields to navigate because they have a special mineral called magnetite above their nostrils. Scientists believe that birds also use the features in landscapes such as mountains or coastlines to guide them. Some birds such as mallards use the stars to navigate while other birds such as starlings use the sun.
Insect eating birds such as swallows and swifts fly by day because they feed on the wing. Hawks and other soaring birds also fly in the day as when there are more warm air currents (also known as thermals) they don't have to flap their wings so much and so use less energy.
Starlings, finches and other flocking birds fly by day and will land every so often to rest or feed before flying off again. Most songbirds such as warblers rest in the day and fly at night when the air is stiller.
How can birds cope with migration?
It is amazing how birds have adapted to fly these long distances. Birds have adapted to survive the
the difficult conditions that comes with migrating often thousands of miles. Most birds that migrate are able to fly high using the prevailing winds and thermals to gain height and distance. Most birds have hollow bones which make them lighter, and some birds are lighter because the essential organs in their bodies are smaller and they have developed larger, more powerful muscles in their breast especially for flying. If you see geese flying they form a 'V' shape and the front or bird leading will change regularly. This reduces drag and they fly in this shape so that it is not such hard work for the birds not at the front. They change regularly so that the same bird is not leading for the whole journey and this way they all take turns in being the leading bird.
Of course before any bird leaves for this very long migratory journey they need to eat plenty of food and build up their fat reserves as many don't eat during the journey. Some birds will double their body weight.
Many birds that migrate travel in large numbers together as this is safety from predators and most birds will stop and rest for a while during the migration.
Other species found in Britain that migrate
Fish such as Atlantic Salmon migrate away from their main feeding areas to somewhere that is safer to breed. This type of migration is known as reproductive migration. The adult salmon live in the Atlantic Ocean but return to the freshwater rivers and streams in Britain to lay their eggs. Amazingly, water must smell to the salmon as they use their sense of smell to find their way back to the river or stream where they were born or back to sea to feed. They lay their eggs in rivers and streams as it is a safer start for the young salmon when they hatch. There are too many hazards and predators for the young salmon in the open sea. The adults reach the river or stream and stop eating when they lay their eggs. The adults then return to the Atlantic Ocean again. The young salmon hatch in the freshwater and spend up to five years in the river or stream before they too make their way to the sea where they stay until old enough to return to the river or stream where they were born.
The adults of European eels go on a journey of between 6,000 and 7,000 kilometres (3,728 and 4,350 miles) from European rivers including those in Britain by crossing the Atlantic Ocean to near the Bahamas in the Sargasso Sea. This can take up to 3 years to complete this amazing journey. In the Sargasso Sea the adult eels lay their eggs which hatch into young. The transparent larvae float across the ocean using the currents and by the time they reach our rivers they are elvers or small eels. They enter the rivers and swim against the river currents and head upstream. The elvers carry on growing up to one metre long and stay there until they start to breed. Sometimes eels will move across land to another river. The eels then head back across the Atlantic Ocean to the Sargasso Sea. They swim at night near the surface where the water is warmer and dive deeper during the day. It seems that during this long journey they do not eat at all. During this migration the digestive tracts of the eels becomes smaller and their eyes grow to four times their normal size. Their pectoral fins grow longer so they become more efficient swimmers.
Of course, some animals such as toads and frogs migrate fairly short distances from where they hibernated under logs and stones to the breeding pond where they were born. You may have seen signs along the roads saying 'toad patrol' and that is where people go out at night and will lift the toads across the road so that they won't get squashed!
Migration is when animals make a special journey to a more suitable environment usually twice a year because of food availability, breeding sites and bad weather. In Britain, when the weather gets colder and the days are shorter animals have a choice between hibernating or migrating to somewhere where food is still plentiful. Some birds are able to adapt and survive the cold weather here but others fly to warmer parts of the world because they are insect eaters and need to have a ready supply of food. In winter insects die or hibernate. Also the weather is just too cold for some of the young to survive. But why do birds leave warmer countries such as Africa to return again in spring to breed in Britain? After all, there is still plenty of food there. They come back to Britain because there are less predators and less competition for food and space to breed and raise their young. The days are longer in Britain during the summer months so there is more light to be able to find food to feed their young. In autumn we also get birds that migrate to Britain from Scandinavia and Russia because our weather is much milder and they have the food here that they need to survive.
Types of migration
There are three kinds of bird visitors that migrate to and from Britain.
Winter Visitors
Birds such as many of the ducks and geese, whooper swans, fieldfare and redwing fly to Britain from colder countries in the north such as Scandinavia and Russia because there is more food available here. Many of these countries have snow and ice for much if not all of the winter. They return north in the spring to breed.
Summer Visitors
Birds that come to Britain to breed here during the summer come from countries that are farther south such as Africa and Spain where it is warmer in winter. These include the birds such as swallow, house martin, swift, sand martin, cuckoo. In Autumn they return south with their young to here there is good source of food. Also birds that have spent the winter out at sea such as puffin and manx shearwater arrive on Britain's coastline to breed.
Passage migrants
These are birds that are either migrating north or south and stop in Britain to rest and feed. This is like us stopping at a Service Station on a motorway for a while during a long journey to eat and rest. These birds are usually seen in spring and autumn during their long journey either north or south.
How do birds know when to migrate?
In Britain it is the season changing. The days getting shorter and the weather getting colder and maybe getting harder to find food such as insects tells the birds it is time to leave. The winter migrants fly back north as the days start to get longer and the British weather starts to get milder.
How do they know the way?
So how do they know where to go? I think bird migration is fascinating. They don't have Sat Navs, maps or even a compass and yet even the young birds who have never migrated know where to go! There are four possible ways that birds navigate. One of the main ways is that is passed down through their genes from their ancestors and it is instinct that they know the route. Some birds use magnetic fields to navigate because they have a special mineral called magnetite above their nostrils. Scientists believe that birds also use the features in landscapes such as mountains or coastlines to guide them. Some birds such as mallards use the stars to navigate while other birds such as starlings use the sun.
Insect eating birds such as swallows and swifts fly by day because they feed on the wing. Hawks and other soaring birds also fly in the day as when there are more warm air currents (also known as thermals) they don't have to flap their wings so much and so use less energy.
Starlings, finches and other flocking birds fly by day and will land every so often to rest or feed before flying off again. Most songbirds such as warblers rest in the day and fly at night when the air is stiller.
How can birds cope with migration?
It is amazing how birds have adapted to fly these long distances. Birds have adapted to survive the
the difficult conditions that comes with migrating often thousands of miles. Most birds that migrate are able to fly high using the prevailing winds and thermals to gain height and distance. Most birds have hollow bones which make them lighter, and some birds are lighter because the essential organs in their bodies are smaller and they have developed larger, more powerful muscles in their breast especially for flying. If you see geese flying they form a 'V' shape and the front or bird leading will change regularly. This reduces drag and they fly in this shape so that it is not such hard work for the birds not at the front. They change regularly so that the same bird is not leading for the whole journey and this way they all take turns in being the leading bird.
Of course before any bird leaves for this very long migratory journey they need to eat plenty of food and build up their fat reserves as many don't eat during the journey. Some birds will double their body weight.
Many birds that migrate travel in large numbers together as this is safety from predators and most birds will stop and rest for a while during the migration.
Other species found in Britain that migrate
Fish such as Atlantic Salmon migrate away from their main feeding areas to somewhere that is safer to breed. This type of migration is known as reproductive migration. The adult salmon live in the Atlantic Ocean but return to the freshwater rivers and streams in Britain to lay their eggs. Amazingly, water must smell to the salmon as they use their sense of smell to find their way back to the river or stream where they were born or back to sea to feed. They lay their eggs in rivers and streams as it is a safer start for the young salmon when they hatch. There are too many hazards and predators for the young salmon in the open sea. The adults reach the river or stream and stop eating when they lay their eggs. The adults then return to the Atlantic Ocean again. The young salmon hatch in the freshwater and spend up to five years in the river or stream before they too make their way to the sea where they stay until old enough to return to the river or stream where they were born.
The adults of European eels go on a journey of between 6,000 and 7,000 kilometres (3,728 and 4,350 miles) from European rivers including those in Britain by crossing the Atlantic Ocean to near the Bahamas in the Sargasso Sea. This can take up to 3 years to complete this amazing journey. In the Sargasso Sea the adult eels lay their eggs which hatch into young. The transparent larvae float across the ocean using the currents and by the time they reach our rivers they are elvers or small eels. They enter the rivers and swim against the river currents and head upstream. The elvers carry on growing up to one metre long and stay there until they start to breed. Sometimes eels will move across land to another river. The eels then head back across the Atlantic Ocean to the Sargasso Sea. They swim at night near the surface where the water is warmer and dive deeper during the day. It seems that during this long journey they do not eat at all. During this migration the digestive tracts of the eels becomes smaller and their eyes grow to four times their normal size. Their pectoral fins grow longer so they become more efficient swimmers.
Of course, some animals such as toads and frogs migrate fairly short distances from where they hibernated under logs and stones to the breeding pond where they were born. You may have seen signs along the roads saying 'toad patrol' and that is where people go out at night and will lift the toads across the road so that they won't get squashed!
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