Born in the winter but how do pups stay warm?
Being fat helps! Seal pups get a good nights sleep even when the ground is frozen
The white soft fur is called lanugo. On the right you can see that lanugo is frizzy and dense. This traps air close to the skin to insulate the pups until they are fat enough.
Thursday 25th November comments (Part I of II): In a two part blog post, we speak to the Seal research team on the island to answer the questions we simply want to know the answers to. Seal expert Kimberley Bennett helps provide the answers to how seal pups stay warm in the cold…
In recent days we’ve had a cold snap overnight on the Isle of May and woke up to thick frost on the ground, followed by howling gales and driving rain. It’s right in the middle of the grey seal breeding season so how do the pups cope with such cold temperatures and miserable weather?
Easy!
Grey seals are well adapted to the cold and in some parts of their range, like the Baltic Sea and the east coast of Canada, they breed on ice. And they live in cold water. Water conducts heat 25 times faster than air and without thick insulation mammals in water quickly lose body heat and become hypothermic. But seals are mammals just like us and maintain their internal body temperature at around 37 °C. So how do they cope with cold?
Be fat! Fat is a great insulator and the blubber layer of grey seal adults and pups from about 5 days old is several centimetres thick. That’s enough to stop a large amount of transfer of heat from the body to either the water while seals are at sea, or to the air while they are on land. If you’re an animal that lives most of the time in water, you don’t have to worry about carrying around the extra weight of fat tissue and it can help with buoyancy because it is less dense than water.
Be furry! Fat is a much more effective insulator than air because it conducts heat less well. But being fat is not the whole story: pups are not fat at all when they are first born and it takes several days to build up a thick enough blubber layer to have effective insulation. In addition, when they are skinny, they have a lot of surface area relative to their size, which means they lose heat faster. So what do they do in those first days after birth? That’s where the lanugo, the soft fluffy white fur, comes in.
The hairs are frizzy and kinked, with a short underlayer and longer soft guard hairs that are packed together densely. Together these layers trap air next to the skin, which makes the coat lovely and warm, so long as its dry! The fur also is coated in water repellent oils that make sure that even when it rains, the soft underhair does not get soaked and the pup still has a layer of air next to its skin. When fur gets really wet, and air is pushed out, the water starts to conduct heat away from the body. Pups moult around the time they wean and the new adult pelage is shorter, sleeker, less fluffy and less ‘wettable’.
So that’s a start! Two reasons how grey seal pups cope with the extremes of temperature and tomorrow we’ll bring you a few more answers to the question of how seal pups survive in the cold!
Isle of May National Nature Reserve 