Great Northern Diver (Gavia immer)
This is really a North American species although it has a small outpost in Iceland, where about 300 pairs breed each year. Several thousand also winter at sea around the coasts of north-west Europe.
To breed successfully this species needs large, undisturbed, deep lakes with a good population of fish. The fish don’t necessarily need to be large; a length of 15-30cm per catch is enough. There doesn’t need to be much variety, either; a pair can sustain themselves and their young on just one fish species, so long as it is abundant. Diving conditions are also important on the home lake, because divers hunt by sight, and need clear water. They often immerse the head and neck before a dive, checking whether any fish are within range; this practice is called “snorkelling”.
The Great Northern Diver is famous for its territorial calls, which include a haunting tremolo wail, often heard, like many diver calls, in the depths of the night.