Night tern departures

BWPi states that most Common tern migration is at night and also that birds depart from Teesmouth to the south-west taking them to Liverpool Bay.

Last night from 19:45 for 30 minutes flocks of Common terns started to flock together gaining height and forming into tighter and tighter flocks as they gained height reaching the cloud base before heading off south-west inland; as they leave the birds give a distinctive chick call which is presumably a contact note given in the moving flocks; this behaviour is identical to that described in BWPi update ---

Migratory Behaviour

Radar-tracked terns (no differentiation between Arctic and Common) crossing south Sweden in late July took off in small flocks during evening, ascended at rates of c. 1.2 m/s to heights of 1000–3000 m flying 12–15 m/s (40–55 km/h) in level flight, suggesting that terns start migratory flights in evening and fly at high altitudes at night (Alerstam 1985), probably to reduce danger of predation, because wind speed decreases in evening, and terns feed during the day ( Johansson and Jakobsson 1997).

the images above attempt to show the birds as they gained height into the night sky

There have also been up to 8 or 9 Roseate Terns and 8+ Black terns in recent days but very few Sandwich or Arctic Terns