Radio sends birds off course

13 May 2014

Interview with

Henrik Mouritsen, University of Oldenburg

If you listen to the Naked Scientists on a radio over medium wave, the transmissions you're tuning in to might be interfering with the migration patterns of nearby birds, according to research from Germany.

European Robin (Erithacus rubecula) © Francis C. Franklin

A team there were studying the direction that robins set off on their migration journeys by putting the birds in small funnels, called orientation cages, in darkened huts. But something was wrong, as the birds didn't seem to know where to go - until they tried screening out electromagnetic radiation - or radio waves - from the huts, by surrounding them with a shielding device called a Faraday cage.

Kat Arney spoke to lead researcher Henrik Mouritsen.

Henrik - For the 2 to 3 years, we couldn't get the birds to orient in these orientation cages that we used to test their behavioural preferences. And that's very strange because that experiment has worked all over the world for about 40 years. Any time we tried them for a descent amount of time, they would basically just one day jumping in the direction, the next day jumping in that direction, and that's not what you would normally expect. The birds show migratory restlessness and it's directed in a direction in which they want to fly. So normally, they should jump to the northeast in spring and the southwest in autumn, but they didn't do it.

Kat - So, what gave you a clue that there was something maybe interfering with the bird's migration system?

Henrik - Well, it was obvious that there was something we were doing wrong because I had done the same experiments in Denmark during my doctoral thesis and there, those experiments worked fine. So, we tried all kinds of things. We changed the food, we changed the cages, we changed the light in the room. We changed a lot of different things and nothing seem to help until one day, a post doc of mine got the idea that maybe we should try to screen it like do the Faraday cage around our setup so that electromagnetic noise was screened. Honestly, I didn't think the likelihood that this would make any difference was very large, but by that time, we were willing to try almost anything to get these birds to show their natural behaviour.

Kat - And so, once you started screening out the electromagnetic fields, what did you start to see?

Henrik - The birds started to orient just as they were supposed to do with what they had done in my experiments in Denmark. I was like, "Really?" That was very unexpected and anyway, I was happy because we could start doing those experiments that we had wanted to do all the time. So, that's what we did first. We focused on doing the experiments we have been planning all the time.  it was also immediately clear to me that if the improved orientation was really due to the screening of the electromagnetic noise then that was a very important finding in its own right. So, a year later, we tested that more directly by just thinking about the prediction that a Faraday cage only works when it's grounded. Basically, if you disconnect the grounding of the Faraday cage then it doesn't screen anymore. So, we basically did the simple experiments of disconnecting or connecting the grounding without the students doing the experiments knowing that we were doing it. And suddenly, it became clear that on the days when they were tested ungrounded that they were random and on the days they were grounded, they were oriented very fine.

Kat - Were there any particular frequencies that you found were interfering with the birds?

Henrik - We see an effect of frequencies ranging from about 50 kilohertz up to about 5 megahertz when we can be sure that it's not the power lines for instance because the frequency of power lines is typically 16.7 hertz or 50 hertz, or much, much lower frequency. We can also say that it's not mobile phones because mobile phone communication takes place in gigahertz range so billions of hertz. So basically, it's middle wave radio.

Kat - What do you think are the implications of this if sort of radio signal produced by regular radios, all kinds of electronic devices interfering with some birds migration?

Henrik - Well, they only do so very close to the source. So, the birds seems to have only a problem in urban areas, not in rural areas. It could also be a more serious problem if for instance, the birds determine their flight direction prior to takeoff and then they keep that direction for a full night then they would fly wrong for a full night if they were sitting in an urban area in case it's overcast because birds have more than one compass. They have a magnetic compass, a star compass and a sun compass. As long as they get good information from one of them, they are generally okay finding their right migratory direction. So, I don't know how big this effect would be on wild birds, but I'm pretty sure the birds would find it better if they could use all their navigation systems at all locations at all times.

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