How do millions of birds travel thousands of kilometres and make a return trip to the same nesting site each year? Maybe they have some sort of hidden satnav that humans know nothing about or some other mysterious means of guiding them across oceans, writes Donal Hickey
There was once a common belief that migrating birds hitched lifts on ships which enabled them to get 5,000km across the Atlantic from North America to Ireland. The theory did not stand up to scrutiny. Nobody, for instance, could explain why the wanderers only arrived in migration seasons.
A fascinating new book sets out to tell how these visitors, which come to breed, stop off or spend the winter, reach our shores. They can fly for days in extremely trying conditions but even more intriguing is their homing ability. Many young birds can fly to faraway winter quarters they have never seen and return.
In his book, To the Ends of the Earth — Ireland’s Place in Bird Migration, Anthony McGeehan says birds have an array of senses far exceeding that of humans, taking directional information from the world around them. And, rather than just relying on the sun and stars for guidance, they make use of something we cannot sense, namely the pull of the Earth’s magnetic field.
Swallows, which live here from April to October and winter in Africa, are among our best-known migratory birds. They try to revisit the same locality on arriving in late spring, described by the author as “doubly endearing”.
On how migration started, he says it must have developed because it supported a species and became part of a survival routine. Birds also prepare for long flights, putting on fat as fuel. “Probably, sophisticated globetrotting grew from basic needs, such as finding food. Although not all birds migrate, even sedentary species are capable of exploring pastures new,” he goes on.
Some birds, including American crossbills, become migratory only when there are food shortages and they head west to Europe where they can eat plenty before returning.
Equally fascinating is birds’ ability to sense weather changes. They have sophisticated navigation systems, taking in the path of the sun across the sky and the rotation of a starry sky, but they also need the best weather.
Take sanderlings whose breeding grounds are close to the North Pole. Decisions on departure times are critical. Experiments in Iceland — where they stop before heading to breeding areas further north — found departures were delayed during overcast conditions. That indicated an ability to judge conditions and plan a flight path accordingly.
This beautifully-produced book by the Collins Press is an ideal gift for bird-lovers.