Who's the culprit?

  

This is a scene we came across after finishing field work this morning (9 May 2024).  Some empty-looking whelks (Nucella ostrina) on the sand...and upon closer inspection, their opercula nearby (the operculum is the "trap-door" on the bottom of a snail's foot that seals the opening to its shell when the snail is pulled in).

It looked like the snails had been eaten by a predator, but we couldn't recall seeing this before, so we looked around a little more.

We found even more evidence that something had been eating both whelks and limpets.  Here are a few examples, including snail shells and overturned limpet shells with most of the soft parts missing, but with a thin ring of tissue, evidence that they had been eaten recently:

 

 

So...who was responsible for eating these snails and limpets?

 

We weren't sure, but we kept looking, and Eric eventually spotted a clue.  Tracks in the sand around some of the predated shells:

 

 

 

After thinking through the possibilities, we're guessing these footprints might belong to a rat (!).

 

Rat predation on intertidal invertebrates has been documented previously (Thanks to Sergio!), but we don't recall seeing it locally before.  Maybe because there was a lot of sand at this site it was easier to notice the empty shells and the tracks in the sand.

 

Here's a close-up of one track in case anyone can help us with an identification.  The track was ~1 cm across.

 

 

 

You learn something new every day!