Behaviours of Great Northern Diver

Rhyl, North Wales

Returning on Friday (13 Jan) from a wonderful couple of days in North Wales we called in at Rhyl Marine Lake. The adult Great North Diver still present, eventually came very close. Was able to watch a couple of lovely little behavior traits:

  • Swallowing a crab

  • Losing the Lump

First off the crab.

Diving non-stop for food it surfaced with this crab. Seemed to take a few moments to wash it off in the water before swallowing it whole. I am not sure but, the crab seemed still alive. Quite some feat! I think its a Shore Crab?





Now cleaned, just after this shot the bird turned away and swallowed the crab in one quick movement- amazing!

Losing the lump

Great Northern Divers variable show a big bump of lump on their forehead which at other times is absent leaving a smoothly contoured curved head shape. Here’s the lump showing well:

At such close range it was easy to watch the bump- presumably a set of raised feather- lowered just prior to the birds dive. You can see it happen on the video clip:


6 thoughts on “Behaviours of Great Northern Diver

  1. thedrunkbirder

    When I watched the bird for three days on the bounce I saw it catch plenty of crabs but after washing them it would always submerge to eat them. A few other locals has also noted this.

  2. Marc Hughes

    Amazing pictures Martin of a superb bird.

    It’s an amazing experience watching the bird feed; at times you can hear it crunch the crab’s shell. It also seems to dive with the crab in its beak before swallowing it – anyone know why does it do this?

    Also great video footage from Adrain Foster here – The flattening of the bulbous forehead is very evident. Local birders have been questioning why it does this – streamlining itself? taking a deep breath? Anyone know?

    One interesting observation is the fact that the Diver is now taking 6-7 attempts to catch a crab, whereas when it first arrived it was catching one every 1-2 attempts. I woner if he’s slowly guzzling his way through the Shore Crab population of the lake?

    Unfortunately I heard today that the lake will be drained in a few weeks time, so if you haven’t been to see it yet – don’t leave it too late.

  3. Adrian Foster

    I was wondering whether the “bump” is like a crest where feathers are being flattened or if it is under the skin, perhaps a store for oxygenated blood (pure speculation). It would be great to know the truth.


  4. John Jackson

    Is the diver washing the crab? It looks to me like it is removing the claws and maybe some legs before swallowing. At least that’s how I interpreted similar behaviour by the famous Hayle Estuary White-billed Diver a few winters back.

  5. Chatterbirds

    I didn’t realize that divers eat crabs on a regular basis. I just assumed that fish were the main part of their diet. Concerning the vanishing “lump”, I lean towards the streamlining hypothesis.

  6. Ken Turnip

    It was interesting when watching the Hayle/Carsew Pacific Diver a few years back that I could see no evidence of the ‘thick nape’ that is much vaunted for this species. It was very actively diving at the time and whenever it surfaced it appeared quite sleek and the bill seemed longer, stronger than I had hoped it would appear. After a while, the bird stopped diving to rest and preen. Almost instantly, the nape ‘inflated’ and the effect was to make the bill look smaller. Finally it looked how a Pacific Diver ‘should’. Certainly taught me the lesson that conditions and activity can massively affect appearance of many species.


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