What’s on the menu for mice living on the Antipodes Islands?

 

Dr. Jo Peace, Research Fellow from Auckland University looks at the stomach contents of Antipodes Island mice….

Tools of the trade - each mouse stomach is placed individually in a Petri dish

Tools of the trade – each mouse stomach is placed individually in a Petri dish

“It’s one thing to “know” that mice must be having an impact on native species and quite another to prove it – it takes some fairly glamorous detective work to do so…

So when I was presented with ten small tubes each containing a mouse stomach, the past owners formerly of the Antipodes Islands, I put on my lab coat and my Sherlock Holmes hat!

Firstly a mouse stomach is small, so the whole procedure is pretty fiddly stuff –

The size of the mouse stomach (~1cm2) means that everything inside is even smaller. The first puzzle is to get the stomach contents out of the stomach and separated from any bait, e.g. sticky, oily, peanut butter, that was used to catch the unlucky individual.

You may never look at a tea strainer in the same way again! The stomach contents are rinsed to remove tiny fragments and as much peanut butter as possible.
Mouse stomach carefully opened to allow the contents to be emptied out

Mouse stomach carefully opened to allow the contents to be emptied out

Tea's up!

Tea’s up!

 Then it’s to the microscope to have a good squint at the remnants of the last meal. Enter laptops and reference photos onto the crime scene to log the records and help decipher what the mangled little bits of everything might be…

CSI eat your heart out

CSI eat your heart out

The contents of one mouse stomach spread out on a Petri dish

The contents of one mouse stomach spread out on a Petri dish

First the contents are estimated so we can think about diet in general – what proportion of this mouse’s last meal was invertebrates? Or vegetation? Is there evidence of vertebrate remains? These mice from Antipodes Island favoured invertebrates slightly over vegetation and vertebrates with the majority of stomachs containing invertebrate remains. However it was interesting to find feathers in four of the stomachs examined.

Then the invertebrate bits are counted and identified as well as possible. A minimum number of each general type of invertebrate is estimated. For example if I find seven beetle legs I can safely say the mouse chomped at least two beetles. Luckily for us we found the remains of three weevils that still were intact enough to be identified through to species.

It’s a painstaking process

It’s a painstaking process

Three unlucky weevils

Three unlucky weevils

Along with these unfortunate weevils there was evidence of maggots, caterpillars, mites, spiders, and worms. These mice are certainly managing to find a good variety of food out there. Or at least they were before they were caught!”