The natural environment is deeply connected to the climatic conditions and it’s no different here at Londolozi. Being out and about for six to eight hours a day on safari, we are fully immersed in our surroundings and bear witness, first hand, to the plants and animals reacting accordingly to the imminent roll over from rainy season to dry.
For most, the time of plenty has come to an end and so measures need to be taken to prepare for the coldest and bleakest months. A number of strategies are taken up, but none quite so fascinating than the migratory bird species.
Bird migration was one of the major mysteries of the natural world for centuries. People were baffled as to where the birds disappeared to for half the year. Ancient Greeks speculated that they in fact hibernated through the winter while some even believed that they metamorphasized into other animals. Fortunately, over the centuries and with the modern technology we have today, we have solved the majority of the bird migration mysteries, however, one question still remains – how do the birds know where to go?
The journeys that these birds undertake twice a year are often several thousand kilometers, with some species crossing three continents and an ocean to get to their destination. We as humans also make similar journeys but with the assured assistance of advanced technology and GPS systems that took us ages to develop and design; all the birds have is a fresh set of feathers and a complex combination of instinct and intuition as well as their incredible senses.
We know through observation that the migratory bird species do not always learn their migratory routes from their parent birds because, as is the case with the cuckoos for example, they can be raised by a non-migratory foster parent (this is another fascinating breeding strategy used by some birds known as brood parasitism; a topic for another day) yet still embark north on a migration at the end of the summer. But how do they know where to go without the guidance of a parent?
Three main theories have been proposed as to how the birds navigate their long distance travels. The first of these suggests that the birds – many of which take to the skies under cover of night – rely on the stars to guide them on their journey. It’s quite difficult to actually prove this theory but some studies conducted inside planetariums with migratory birds have seen them align themselves accordingly with the altering star patterns. Personally, I struggle to get behind this theory for a number of reasons – the most obvious being the fact that a few cloudy nights would mean the birds migration would be put on hold. Surely a natural phenomenon as great as bird migration could not be halted by overcast conditions?
The second theory, quite similar to the first, suggests that the birds rely on the sun as their compass. They orientate themselves using the position of the sun in the sky during the daylight hours. A study conducted by German biologist Gustav Kramer found that caged migratory birds that were exposed to the sun ‘showed migratory restlessness in the same direction’ that the wild birds did as opposed to the caged migratory birds that were not exposed to the sun, who showed migratory restlessness in different directions. This theory could also be doubted for the same reason as the one above, however, it has been found that several bird species can in fact see ultra-violet light (a form of light that the sun emits) which penetrates through cloud cover and allows the birds to still see the position of the sun on overcast days!
The third theory, and possibly the most fascinating, suggests that the birds are able to align themselves to the earth’s magnetic field. The earth essentially acts as a large magnet with greater magnetic pull towards the poles and less at the equator. This theory might sound rather far-fetched, but birds are known to have abnormally high levels of trace metal elements in the hippocampus region of their brains that allow them to tap into this magnetic field and get a greater sense of direction. It is a rather complex theory indeed that researchers are still conclusively proving, however, two scholars at Baylor University did manage to prove the presence of magneto-receptive cells in some pigeons brains. An interesting article from the New York Times discusses this theory in more depth.
As soon as one question is answered about bird migration, 10 more are posed. Will we ever know all the ins and outs of their fascinating journeys?
Whether we will or won’t, I still feel like the birds should be lauded for the phenomenal migrations they undertake.
When the first Wahlberg’s eagle rolls in towards the end of August, I may well give it a standing ovation. I doubt it’ll take a bow, but at least the sentiment will make me feel like we’re giving the bird its due…