The challenge of being small

My main research topics all exist around one specific animal, the common shrew (Sorex araneus).

Shrews are bound by an incredibly fast-paced life: they burn through energy so quickly that they must eat constantly just to stay alive. Their metabolism is so extreme that even a few hours without food can be fatal.

This high metabolism makes them particularly vulnerable to seasonal changes, and it makes it impossible for them to hibernate during winter.

Their solution? They shrink.

Unlike animals that grow steadily over years or those that adapt gradually across generations, shrews undergo a radical transformation within a single lifetime.

As winter approaches, their skulls, brains, bones, muscles, and internal organs shrink in size

This process, known as Dehnel’s Phenomenon, is an extreme form of biological restructuring that allows them to drastically lower their energy demands when food is scarce. Then, as spring arrives, their bodies begin to regrow, reversing much of the shrinkage in preparation for a season of rapid activity and reproduction.

How does it work?

Shrews are born in summer, growing rapidly and reaching their lifetime peak in brain size within just a few months. This is the largest their brains will ever be.

As winter sets in, something remarkable happens: their skulls begin to shrink, their brains lose mass, and their bodies become smaller and leaner. These changes reduce their energy consumption at a time when survival depends on making the most of limited resources.

Then, with the arrival of spring, their bodies regrow some (but not all) of what was lost. Their body mass grows to twice its winter size by spring. This allows them to take advantage of renewed food availability and prepare for reproduction.

Shrews live only about a year, so this transformation happens just once in their lifetime.

What does the brain shrinkage and regrowth mean for how shrews think, learn and behave?

The idea that a brain can physically shrink and then regrow challenges many assumptions about cognition, memory, and plasticity.

My research explores what happens when their brain changes size:

How does brain size affect cognitive abilities?

Does a smaller brain lead to simpler decision-making?

When the brain regrows, does it restore lost functions—or does it reorganize in a new way?

These questions go beyond just shrews. Understanding how an animal maintains function despite physical changes in the brain helps us explore broader ideas in neurodegeneration and energy efficiency.

Does captivity influence learning?

Brain size is of course only part of the story.

The environment an animal experiences shapes its brain and behavior. In captivity, animals face new challenges—chronic stress, lack of stimulation, and altered social dynamics. Do shrews kept in captivity learn differently than those in the wild?

I tested the ability of shrews to associate an odor cue with a reward in a Y-maze associative learning task.

Each dot represents an individual shrew’s decision in a trial. The x-axis represents the trial number, from 1 to 10. The y-axis shows whether they made the correct choice (1) or the wrong one (0).

Summer wild (orange) shrews had the highest and earliest success rates.

Winter wild (dark blue) shrews showed a similar learning curve, but they learned at a slower rate and did not reach the Summer success rate.

Winter captive (light blue) shrews showed no learning, never deviating from chance.

📄 This work is published in Royal Society Open Science: Captivity alters behaviour but not seasonal brain size change in semi-naturally housed shrews

Project Collaborators

I conduct this research supervised by Dr. Dina Dechmann at the Max Planck Institute of Animal Behaviour

Collaborators:
Prof. Dominik von Elverfeldt, University of Freiburg, Germany
Prof. Liliana Dávalos, Stony Brook University, New York
Prof. John Nieland, University of Aalborg, Denmark