Some bats can travel very long distances when foraging and migrating between breeding and wintering grounds. A Nathusius’ pipistrelle recently flew more than 600km from Somerset to Holland, for instance, and several European species, such as the greater noctule, can cover more than 1,000km.
How bats safely navigate over these long distances used to be something of a mystery – vision and echolocation are less useful on long migration routes. We now know that bats, in common with many birds, insects and fish, can detect the direction of the Earth’s magnetic field, through iron oxide particles (magnetite) in their cells. This internal ‘compass sense’ is a vital navigation aid, but in order for it to be used effectively, it needs to be calibrated against other navigational cues.
Recent studies on greater mouse-eared bats have found that at sunset the animals use the pattern of polarised light as a clue, even when the sun is obscured by clouds. They are the first mammal species ever recorded to do this. However, how the bats detect the polarised light is as yet unknown.
How to watch birds migrating
The One Show’s ‘Urban Birder’ explains 'viz migging’, or visible migration watching, and how you can watch it.
I always find this time of year hugely exciting. Millions of birds are on the move, leaving our isles heading south or arriving for the winter from the north and east.
The modern term for this kind of birdwatching is ‘viz migging’, or visible migration watching.
What is traditionally known as the ‘autumn’ migration really starts in mid-July, when waders return from their Arctic breeding grounds and cuckoos leave our shores for Africa.
Our briefest summer visitors – swifts – start leaving in August (having only arrived in May), while other migrants such as swallows and warblers tend to hang around a bit longer, some staying into September and even beyond.
Throughout October, most of our ‘overwinterers’, such as white-fronted and barnacle geese and the winter thrushes redwings and fieldfares, start arriving.
By November, the main body of the migration is complete – though, perhaps a bit confusingly, birds will continue to arrive ande depart throughout the winter, especially if there are sudden cold or warm snaps.
If you spend 30 minutes in your garden every morning, you may notice migratory visitors, perhaps willow warblers or blackcaps, foraging, but a visit to your nearest park will enable you to see migration on a wider scale.
Easterly winds and drizzle before dawn often result in ‘falls’ of warblers and other songbirds feeding in the bushes.
A great way to witness daytime migration is to stand on open ground with a good view of the sky or, better still, watch from a hill or a rooftop. From dawn until midday, birds as varied as meadow pipits, chaffinches, winter thrushes and woodpigeons wing their way across the sky.
In this situation, identification can be very difficult, so it pays to accompany more experienced birders who know the calls and flight behaviour of each species.
The thing to remember when observing migration is to expect the unexpected. Favourable weather conditions make flight more likely, but birds often turn up in strange places for no reason that we understand.
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