On harsh winter evenings like this, the courtyard offers everything the wagtails need to survive the night. For small birds that lose heat rapidly, food, shelter and warmth are critical. Floodlights draw insects like winter gnats and moths, while the surrounding buildings block the biting wind and store the sun’s warmth, acting like giant radiators. Heat also spills out from shop doors as customers come and go. Within this sheltered pocket, the trees provide elevated perches, safely beyond the reach of prowling cats and urban foxes.