Posted on April 24th 2022
Every year, millions of animals carry out the challenging strategy of migrating. The movement of birds, mammals, fish and insects is a key part of the earth’s biodiversity.
Migration to warmer climates
In the UK many birds migrate to warmer climates and then return in the Spring to their breeding grounds. The UK is also the ‘warmer winter home’ to some birds that prefer to winter here such as robins that may have travelled from Russia, Germany or Scandinavia.
Migration in most cases is an incredible challenge. For small animals such as birds that return to the UK from Africa or Southern Europe they need to be able to navigate to precisely the same place every Spring. How they do this has been only speculation for many years.
Recent evidence however has opened up new thinking when it comes to how small animals with seemingly small brains can travel vast distances to return to the same spot. These animals cross mountains, oceans and deserts without getting lost…how do they do it?
Natural map and compass
It is thought that birds use the environment around them to navigate and guide them. They use things like the stars and the Earth’s magnetic field to provide them with something equivalent to a map and compass.
A research team carried out some experiments using reed warblers, which are small European songbirds. Their ability to sense earth’s magnetic fields was disrupted using a small magnet attached to their heads. In addition, they had the stars obscured from their view. The result was that they couldn’t locate the right direction to migrate.
Another study showed how reed warblers can recalculate where they are when they are blown off course or need to detour around barriers such as mountains. Researchers placed the birds within artificial magnetic fields representing a bearing far northwest of the birds migration route. They then measured to see where the birds would orientate themselves for take-off. The birds all changed their orientation from southeast to southwest suggesting they knew to re-calibrate and clearly recognised the magnetic field as foreign to their usual surroundings.
Clearly both the stars and earth’s magnetic field are important cues for birds to migrate. But humans have the potential to disrupt these. For instance, ambient light from cities at night reduces their ability to see the stars and the moon. In addition, artificial electromagnetic signals such as those from radio towers or from everyday items such as electric currents from kettles can also confuse birds ability to read magnetic fields.
As we learn more about the systems that animals use to navigate we are able to learn more about how human activity can impact that natural movement. So much of our pollution is highly visible but those that relate to impacting navigation ability is far more subtle but vital for us to understand so as to reduce our impact on other species.