Exploring bird migration - and the human impact

Exploring bird migration - and the human impact

Oct 14, 2019

With World Migratory Bird Day falling in October Meryl Batchelder considers why birds migrate, what threats they face on their journeys and how climate change may affect them. She draws parallels with human migration and the tradition of holiday makers to seek out warmer climes in the winter.

Travelling south for the winter sun

The young ospreys which hatched near Kielder Water in Northumberland this spring have flown their nests over the past month. All they have ever known is a little corner of the North East of England. Their parents have looked after them from when they first emerged from their eggs, nurtured them as chicks and taught the fledglings how to fly, soar and hunt. They have now started on a perilously long journey to their wintering grounds in Africa. They have no map, no Sat-Nav, no experience – just an innate, biological compass that pushes them south. They are migrants looking for food and warmth during the winter months.

The ospreys travel solo; adult females fly first, followed by the males and then the young. After crossing the English Channel, they fly down through France and Spain into North Africa. Some cross the Sahara, while others trace the West African coastline, their winter destinations are countries such as Senegal and Guinea. Ospreys travel by day, using thermals to gain height over land and travel around 6,700 km (4,200 miles) at a rate of roughly 260 km per day. Their incredible, southbound journey, complete with a few resting stops en route, takes around 45 days in total.

Celebrating and Protecting Migratory Birds

World Migratory Bird Day is an annual awareness-raising campaign highlighting the need for the conservation of migratory birds and their habitats. The international day unifies the planet’s major migratory bird corridors. The route the ospreys travel is the African-Eurasian flyway but there are also the East Asian-Australasian flyway and the Americas flyway. Celebrated twice a year, on the Second Saturday in May and in October, World Migratory Bird Day aims to encourage the conservation of birds that migrate.

The second World Migratory Bird Day this year falls on Saturday 12 October and the theme is ‘Protect Birds: Be the Solution to Plastic Pollution!’. With an annual production of more than 300 million tonnes, plastic is one of the most widely used materials in the world. Lightweight and designed to last, discarded pieces of plastic are readily transported through the forces of nature. The plastic causes serious threats to migratory species around the world. Birds can become entangled in fishing nets or may directly ingest indigestible floating debris.

To make matters worse, plastic breaks down into small particles by water, sunlight and wind. For birds that eat fish, bioaccumulation of these plastic fragments occurs up the food chain; fish eat small bits of plastic which becomes trapped in their gut, the birds catch and eat the fish, and the plastic accumulates. The plastic makes the bird feel full but provides no nutritional benefit. Eventually it will cause the bird to die of starvation before it is able to breed or it may regurgitate plastic particles into the mouths of its young. It is estimated that 8 million tonnes of plastic enters the oceans each year and the number of seabirds tragically dying from the effects of plastic is one million per year and growing.

Incredible journeys

Bird migration is a regular seasonal movement, often north and south, between breeding and wintering grounds. Although the return journeys carry a high cost in terms of mortality, including from hunting by humans, the birds are driven primarily by availability of food. Much of the science of migration is not fully understood but it seems to be controlled by changes in day length. The birds navigate using the sun and stars, the Earth's magnetic field, and, for those who have made the journey before, mental maps. Around 1800 of the world's 10,000 bird species are long-distance migrants. The Arctic tern holds the furthest migration record for birds, travelling between the Arctic breeding grounds and the Antarctic each year.

As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. The advantages offset the high stress, physical effort, and other risks of the migration. Unlike our ospreys most birds migrate in flocks. For larger birds, this reduces the energy cost. Geese travelling in a v-formation may conserve up to 20% of the energy they would use if they flew alone. Bird migration is not limited to birds that can fly; species of penguin migrate by swimming, their routes can cover over 1,000km and, in Australia, emus have been known to walk around 500km to find plentiful food or water supplies.

Threats to bird migration

In addition to plastic pollution many other human activities threaten migratory bird species. The distances involved mean that they often cross political boundaries of countries. This is why international cooperation is needed to protect different species. Structures such as wind farms, power lines, and offshore oil-rigs have been known to affect migratory birds. Other hazards include storms, wildfires, pollution, and habitat destruction along their migration routes, meaning that the birds cannot find enough food at stopover points resulting in a lack of energy for the next stage of their journey. Some spectacular migrants have already disappeared; during the passenger pigeon's migration in North America the enormous flocks were up to 300-miles long, taking several days to pass – they were hunted to extinction at the turn of the last century.

Global heating, and the resulting change in climate, has begun to affect the timing of migration. In addition, many bird species seem to be expanding their range as consequence of climate change. The increasing intensity of storms may disrupt their journeys and drought will make food scarcer. The speed at which the planet’s weather patterns are changing means that current legislation and protection mechanisms are slow to recognise the concept of shifting patterns in migration from climate refugee birds.

Drawing parallels with human migration

Until recently most human migration has related to economic or political migration – people have moved away from their homes because they were searching for financial security or were trying to escape from fighting and war. Increasingly environmental factors relating to climate change are beginning to drive mass human migration.

People from Central America are trying to move north as continued drought has caused repeated crop failures. Residents of Grand Bahamas have been left homeless from Hurricane Dorian. Sea level rising is forcing coastal populations including some entire Pacific island inhabitants to consider abandoning their low-lying areas.  

Experts at the UNHCR (United Nations High Commissioner for Refugees) explain ‘The Earth’s climate is changing at a rate that has exceeded most scientific forecasts. Some families and communities have already started to suffer from disasters and the consequences of climate change, forced to leave their homes in search of a new beginning.’ If global warming gas emissions continue at the present pace, the number of environmental migrants to Europe could increase by nearly 200 percent.

Whereas bird migrations have a return journey, for example the ospreys usually arrive back in the UK from late March, many human migrants are on a one-way journey and are unable to return as their homes are no longer safe. This is a big difference between natural bird migration and the environmental migration that millions of humans will endure over the coming decades. However, both the migrant birds and refugee humans are just endeavouring to survive.

Feathered or metal wings

An increasing number of people travel recreationally from the UK for a week or two in warmer climes. Like our migratory birds they are searching for some winter sun but don’t fly using their own wings. They fly in planes that contribute to climate breakdown as they emit particles and gases such as carbon, water vapour, hydrocarbons, carbon monoxide, nitrogen oxides, sulphur oxides and carbon which interact among themselves and with the atmosphere.

In the EU, greenhouse gas emissions from aviation have more than doubled in the past 20 years and the aviation industry plans to double in size again over the next decade or so. How do the flights of the soaring but threatened Kielder ospreys and those of the fun-seeking holiday-makers compare? Both are looking for winter sun but one does so for continued existence the other out of desire for a little adventure or rest and relaxation.

With our wonderful migratory birds on the wing facing additional challenges from plastic pollution and climate change they need more protection than ever before. Watch out for the last geese flying south, wish them ‘bon voyage’ for their travels, image the sights they will see on their incredible journey and look forward to the spring when hopefully they will safely return.


Taking learning further:

Support World Migratory Bird Day – take action and show support: http://www.worldmigratorybirdday.org/

Fight plastic pollution

  • Reduce, reuse and recycle - Limit your use of plastic materials and replace them with eco-friendly alternatives, use and dispose of plastics sustainably
  • Clean up - Join clean-up activities in your area, whether at beaches or along rivers
  • Spread the word - Support local and global action against plastic


Research human migration relating to climate change:

  • Which counties are people leaving?
  • Why do people need to leave their homes?
  • Where are they trying to reach?
  • What are the causes and threats that are met en route?
  • Who is responsible for helping them?
  • Can you identify the similarities and differences in the challenges faced by environmentally displaced people as compared to those displaced by war or persecution?

Identify alternatives to flying for recreation:

  • What other ways can we travel?
  • Can you plan a trip to West Africa without using a plane?