Delayed Implantation – I Bet You Don’t Know What It Is

delayed implantation

A baby seal. Photo via Flickr.

Delayed implantation is a term that I had never heard until recently.  It is something that has to do with reproduction for mammals.

Baby animals are always cute to look at and fun to watch.  In the spring it is always fun to look around and watch for baby animals.  Many, but not all mammals give birth to their young in the spring when there is lots of food around.  I recently learned about delayed implantation, which partially explains for why there are so many babies in the spring.

What Is Delayed Implantation?

It is a way that a female, that has already mated, delays growing a baby inside her body.

Normally, a female and male will mate, which means the male’s sperm fertilizes the female’s egg.  Then the fertilized egg will grow into a baby inside of the female.  However, delayed implantation simply means that the fertilized egg will not immediately begin growing into a baby.  In some cases, it may never happen.

delayed implantation, grizzly bear

Grizzly bears are one of the Rocky Mountain mammals that have delayed implantation.

Why Do Animals Have Delayed Implantation?

There are two main reasons that animals have this reproductive strategy, both of which give the babies and mom the best chances to survive.

The first happens when a female is still nursing her babies.  If a female mates and her egg becomes fertilized while she already is nursing and raising babies then delayed implantation occurs.  This prevents her from having more babies while she is already raising some.

The second reason is so that the animals give birth to their young at the best time to give the babies a greater chance of survival.  This may coincide with the time of year when resources or food is most available.

What Animals Practice Delayed Implantation?

There are more than 100 different kinds of mammals that practice it.  These include very different animals such as seals, mice, skunks and bears.

In the Rocky Mountains some of the animals include skunks, mice, brown bears (grizzly) and black bears.

You can learn more about black bear cubs here.