Oyster Dinner

[britnik]

Today out in the woods we found quite a few areas with oyster shells scattered around



Some of the shells seemed to be chewed at one end as below



We are in middle Berkshire so a long way from the sea.

These were all close to a lake so assuming they are freshwater oysters from the lake
Any idea who has been having an oyster dinner?

[The Woodman]

Without any more detail the shells appear to be one of the freswater bivalves, perhaps younger Swan Mussels. There are several similar species. You mention "lake", if there is one not too far away this species would be a likely candidate.

As to what or who ate them, there have been similar questions asked on WAB before. A closer examination of the shells exterior surfaces might reveal beak or tooth marks. The end of the shells appear to have been chewed or pecked away giving access to the inside and facilitating pulling or levering the shell open.

[shenk1]

At Old Moor rspb last Monday a crow was seen flying high with some then dropping them to break them open

[britnik]

Thanks to The Woodman and shenk1 for there interest and help.

This pic may help identify the predated bivalve, length around 2.5 - 3 inches


You learn something everyday, I had never heard of a Swan Mussel and had thought that mussels were confined to the seashore.

[The Woodman]

I think that's a 3+ year old Swan Mussel. The puncture marks are clearly visible on the widest point of the shell perhaps indicating the grab of a canine toothed predator. If corresponding marks were found on the other half then I might be convinced!

There may be several situations to consider.

1.The location of the nearest population of the mussels. Mammalian predators wouldn't carry their prey too far.

2.How did the predator get the mussel? i.e. was it underwater buried in its native substrate or perhaps exposed on dumped dredgings. This makes the choice of ID'ing the predator easier.

3. The last image doesn't show the damage at the apex of of the shell as in the earlier images.

4. The earlier images don't appear to show the marks that the last image does.

5. There may be more than one predator at work here indicating that the mussels were not taken from their native habitat.

6. The location of the observed shells. To me it looks like they're on the littered floor of a softwood plantation. If taken by otter it would be usual for them to take their prey into or under a secure location - bankside shrubbery for example.

7. From the attitude of the shells they appear to have been dropped from above - no scuff marks in the leaf litter which might make think that the culprit might be avian rather than mammalian but I'm open to persuasion. Of course, it all depends on when the shells were left, settlement of litter, depostion of fallen litter, etc.

Fascinating subject britnik.

[britnik]

A little more info

The collections of shells were found while walking round a lake, approx 600ftx500ft.

The first shells were noticed near a pile of logs/sticks in rough grass approx 30ft from the bank of the lake. It was strange that the shells were located in a small area rather than spread out.

Further round the walk not really on a path but up a steep bank from the lake in a wooded area there were multiple small collections of the shells. If this had been a mammal it would have had to leave the water move through a covering of scrub and climbed a steep bank to get to the wooded area.

There were no signs of dredging so I would expect that the predator would have had to fish for the bivalves itself.