Would agree with that based on my observations. The main exception from that typical behaviour I saw in Cornwall a couple of years ago, the White-billed Diver on the Hayle Estuary spent plenty of time on the surface because it was eating largely crabs.
divers do eat the majority of food under water,unless its a big item then they bring it to the surface,but most small fish etc would be swallowed under water.
I was watching the Great Northern Diver at Hollingworth Lake today for more than an hour and it spent at least as much time under the water as swimming about on the surface. Not once did I see it reappear with food in its bill. Does this mean that it was unsuccessful on its fishing dives, it didn't go fishing each dive or do they eat their catch whilst still under water? Anyone have a thought on this point please
Hi Sid,
Can't claim to be an expert on this topic - so delved into my copy of Birds of the Western Palearctice interactive which says this about its diet...
"Primarily fish up to 28 cm, but varies with locality and season, and diet can include crustaceans, molluscs, annelids, insects, and amphibia. In some breeding areas where no fish occur, crustaceans, insects, and molluscs taken instead...... When searching, regularly dips bill and forehead underwater before diving silently from surface. Feet used in propulsion but, particularly in spurts and turning, also wings. Small fish swallowed under water, larger or spiny fish and crabs brought to surface and mutilated before swallowing"
One thing I did personally notice in watching diving birds at Hollingworth Lake and at Piethorne was that it was usually foraging alone - ie not surrounded by Black-headed Gulls! I understand that Goosanders generally return to the surface with their catch to eat it there.....hence the obligatory gulls trying to steal a free lunch! I assumed from the fact that the diver(s) were not surrounded by gulls that they swallowed their catch underwater and that the gulls knew this and hence didn't even bother trailing it! Maybe putting two and two together and making three but they were my personal observations.
Hope this is of some help.
Best wishes,
Bill.
-- Edited by Bill Myerscough on Wednesday 2nd of December 2009 07:33:22 PM
I spent nearly an hour watching it at the weekend as well Sid and I noticed one occasion where it bought a fish to the surface and quite a lot of times when there would be an obvious swirl on the surface and a lot of tiny bubbles - I guess this could just be as the plumage loses trapped air during a dive but I did wonder at the time whether it was indicative of say catching a fish and air being released from the diver's bill as well as maybe a swim bladder or similar from a prey fish?
I was watching the Great Northern Diver at Hollingworth Lake today for more than an hour and it spent at least as much time under the water as swimming about on the surface. Not once did I see it reappear with food in its bill. Does this mean that it was unsuccessful on its fishing dives, it didn't go fishing each dive or do they eat their catch whilst still under water? Anyone have a thought on this point please
