Why do pied wag­tails gather in city cen­tres?

BBC Wildlife Magazine - - Discover Wildlife -

The sight of pied wag­tails roost­ing in the cen­tre of a busy city is one of our more un­usual wildlife spec­ta­cles, most likely seen dur­ing the cold­est months. The birds are tak­ing ad­van­tage of the heat lost from homes, shops and of­fices, which can lift the am­bi­ent tem­per­a­ture to sev­eral de­grees Cel­sius above that of the sur­round­ing coun­try­side, a pat­tern known as the ‘ur­ban heat is­land ef­fect’.

The pied wag feeds mainly on small in­ver­te­brates, which are acutely vul­ner­a­ble to win­ter tem­per­a­tures. This is why much of the north­ern part of the species’ breed­ing range within Bri­tain is aban­doned out­side of the breed­ing sea­son. Many birds move south to the low­lands, form­ing large roost­ing flocks that gather in low bushes, reedbeds and, on oc­ca­sion, city-cen­tre trees. One flock once even found its way into a com­mer­cial green­house.

Mike Toms

BBC Wildlife


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