Great bustards in Spain ‘run’ into electricity en route
We know the big names in animal long distance flights. Jaws drop when we hear that the tiny arctic tern flies between Greenland and Antarctica every year, a round trip of 71,000 kms! Other magnificent animals – humpback whales, monarch butterflies, hordes of wildebeest – travel across the world breaking man’s geographic and political boundaries effortlessly. But one of our many inventions, electricity, might be in the way of animal migrations, literally. Over 20 years, scientists in Spain have studied the threatened Great bustard, a heavily built bird standing tall at about one meter. In their quest to understand the bustard’s migration patterns, they discovered at least one major cause of mortality – collision with power lines.
First, some basic facts: These birds are reluctant fliers. At the study site in central Spain, some birds are sedentary and don’t
migrate all their life, while others migrate distances up to 100 km every year. Young birds figure out their ‘lifestyle’ choice by age 3 –whether or not to migrate, how far to fly, in which direction, and so on. Genetics plays a part of course, but scientists have found that in this species, social learning plays a much bigger role. For instance, if a young bird interacts more with a sedentary adult, it tends to be sedentary all its life. If it hangs out more often with migrating adults, it will probably join their camp.
The study’s big question was to see if and how human causes of mortality affect this migration pattern. The scientists attached radiotransmitter backpacks on 180 birds and traced them from the ground, through telescopes, even from an aeroplane! They also counted the number of birds at the breeding site before and after migration, every year for 16 years.
They found that migrants died earlier and more frequently than sedentary birds. And almost 40% of the deaths were caused by colliding with power lines. There is no doubt that power lines are a direct threat to these birds.But there is another important finding. Over the 20 years of observation, they found that the mixed population of migrants and sedentary birds no longer remained truly mixed. The tendency to migrate dropped drastically; more birds chose the sedentary lifestyle. Remember,young birds learn from those around, and with more migrants getting killed by power lines, it is easy to imagine that they followed the survivors, the non-migrants.
Whether this species will eventually become completely sedentary is hard to know, and will require many more decades of study. But if they do, it could be disastrous. Migration helps maintain genetic diversity by allowing gene flow across populations. Without this, animals would be more genetically similar to each other, and if one contracts a disease, others could become susceptible, and before we know it, entire populations could be wiped out. Many species have gone this route before and some have been lost forever, but there is still time to save this endangered species from going extinct.
Palacin, C, JC Alonso, CA Martin and JA Alonso. 2016. Changes in bird-migration patterns associated with human-induced mortality. Conservation Biology 31: 106-115.
Divya Ramesh studies predator-prey ecology at Indiana State University, where she tries to write, among other things, firstname.lastname@example.org.