Do Any Animals Shrink When the Seasons Change?

It turns out that the common shrew is pretty shrewd. In a study published in the journal Current Biology in October 2017, researchers reported that the size of the tiny mole-like animal’s braincase shrinks by almost 20 percent in preparation for winter. Then, as spring approaches, its skull expands, almost reaching its original size. In fact, shrews lose significant overall body mass -- including the size of their brains, organs, and spines -- in order to conserve energy and limit food requirements as the cold season approaches.

When size matters:

• The scientists studied shrews of all ages to make sure that the shrinkage was seasonally triggered, rather than just being a function of age.
• In the 1940s, Polish zoologist August Dehnel reported on the unusual braincase shrinkage, now called the Dehnel phenomenon. The new research clarifies the extent of the morphing.
• Shrews are found all around the world, and they are among nature’s few venomous mammals. They are known for their ferocity, earning the nickname “tigers of the small animal world.”

Frequently Asked Questions

Do any animals actually shrink with the changing seasons?

Yes, some animals do shrink with the changing seasons. Notably, the weasel family, including stoats and least weasels, can experience a reduction in body size during winter. This phenomenon, known as Dehnel's Phenomenon, helps them conserve energy and maintain body heat in colder climates.

What is Dehnel's Phenomenon?

Dehnel's Phenomenon is a seasonal size change observed in some small mammals, particularly within the weasel family. It involves a reduction in body size, including the skull and other organs, during winter months. This adaptation is thought to be an energy-saving strategy to cope with harsh environmental conditions.

How significant is the size change in animals that shrink seasonally?

The size change in animals that experience seasonal shrinkage can be quite significant. For instance, the common shrew can reduce its body size by up to 20% during winter. This dramatic change includes a reduction in the size of the skull, spine, and major organs, according to research published in scientific journals.

Are there any birds that shrink seasonally?

Yes, some bird species also exhibit seasonal shrinkage. The Great Tit, for example, has been observed to undergo a reduction in brain mass during winter months. This adaptation is believed to be a response to the energetic demands of maintaining brain tissue when food resources are scarce.

Does seasonal shrinkage affect the animal's overall health or lifespan?

Seasonal shrinkage does not appear to adversely affect the overall health or lifespan of the animals that experience it. It is an adaptive response that allows them to survive periods of food scarcity and cold weather. The animals typically regain their size when conditions improve, suggesting a resilient and dynamic biological process.

Is seasonal shrinkage a common trait among animals worldwide?

Seasonal shrinkage is not a common trait among all animals but is observed in certain species adapted to environments with significant seasonal changes. It is more frequently documented in regions with harsh winters, where animals face considerable survival challenges due to temperature fluctuations and food availability.