Every time I spot a poor little skinny hedgehog out and about in November, I ask myself why? After 15 million years why haven’t hedgehogs stopped having babies so late in the year when they stand next to no chance of surviving the winter? It seems like a massive evolutionary fail: nature at her most cruel. But when you take a closer look, the picture may not be as bleak as it seems.
Why Do Hedgehogs Have Late Litters?
The vast majority of adult female hedgehogs start the courtship process pretty much as soon as they come round from hibernation in the spring. The result is a litter of babies in the early summer – June or July. These hoglets have a good few months to grow up and fatten up before hibernation in the autumn.
Once the first litter are weaned, over 80% of female hedgehogs will start on a second litter. These hoglets will be born much later in the year—any time from August to November.
The Problem with Late Litters.
The problem with late litters is a double one.
First, the hoglets, born late in the year, have very little time to put on the weight they need to survive hibernation. To safely go into hibernation, a hedgehog must lay down a good store of fat to give it the energy it needs to see it through the long winter months when it won’t be eating.
Hoglets weigh just a few grams when they are born. They are tiny. To safely hibernate, they need to weigh between 500 and 700 grams. That’s more than a can of beans and takes them to the size of a small loaf of bread.
For hoglets born in September or later, there is very little time for them to do all the eating they need to before their natural food sources dry up and the weather turns too cold for them to be out and about.
The result is that they will hibernate before they have enough weight to see them through the winter and simply not wake up.
Or they will keep searching for ever more scarce food in increasing frigid weather and die of exhaustion or hypothermia.
Hedgehogs do not breed in their first year. So, from an ecological point of view, a hedgehog that dies before hibernation has made no contribution to the survival of the species. A truly wasted life.
Added to the problems the Autumn Juveniles face, late litters put the mother at risk too. The process of nesting, being pregnant, giving birth, feeding and raising a family is exhausting. Females lose weight and condition. Females typically hibernate later than males, so they have the chance to get back to a good weight after raising hoglets. But a very late litter, or the early onset of winter, could compromise the mother’s ability to hibernate safely too.
So why do hedgehogs keep doing something that seems like such a bad idea for the survival of the species?
No Mating Season
Whilst most creatures have a “season” when they mate, hedgehogs, like humans, don’t. Hedgehogs are sexually active pretty much all of the time that they are not hibernating.
It used to be thought that only females who had failed to have an early litter “tried again” later in the year. But more recent research has shown that over 80% of adult female hedgehogs will have a second litter.
Hedgehogs in New Zealand’s North Island, who don’t hibernate because the weather is so mild, often have 3 litters per year.
So it looks like hedgehogs are just programmed to keep mating unless they are hibernating.
It’s a Numbers Game
In nature, the purpose of each animal is to breed and contribute to the continuation of the species.
The younger a female can produce, the greater the chances of her genes being carried into the next generation.
And although Autumn Juveniles, the products or late litters, may not have much chance of making it through the winter, some of them certainly do.
So for the female, the late litter is a risk worth taking, even if it is a risk to her own life.
Not Such Bad Odds?
Encouragingly, a recent study by Toni Bunnell has shown that the odds may not be so badly stacked against autumn juveniles as we thought.
In a study of healthy juveniles brought into her rescue centre, Toni found that autumn juveniles put on weight significantly faster than hoglets born earlier in the year.
Further research is needed to find out exactly why this is. But theories so far suggest it could be due to changes in daylight hours and temperature signalling the onset of winter and stimulating the hogs appetites.
Whatever the reason, this research shows that hoglets in late litters may have a better chance of survival than we had thought.
Not a New Problem
When I see a struggling hoglet in the autumn, I can’t help seeing it as part of the reason why hedgehogs are endangered.
But of course, it’s not. Hedgehogs have probably been having late litters for 15 million years. It is undoubtedly sad that so many young hogs die each year. But it’s not a new phenomenon. It’s part of the hedgehog’s natural life cycle and not part of the reason their numbers are declining so much.
A New Opportunity?
Whilst autumn juveniles have probably been around for millions of years, human hedgehog rescuers and hedgehog champions are a new thing.
A skinny hog out in the autumn here in the UK now stands a good chance of being spotted by a helpful human: taken into care and fattened up for hibernation, or cared for for the whole winter.
This has to mean that increasing numbers of juveniles who, if left to nature would have died, are now surviving their first winter. And then having the opportunity to breed and do their bit for the survival of the species.
So when we help those skinny little autumn juveniles, we are not just helping to undo some of the damage mankind has done to hedgehog kind. We are doing something that has the potential to make a massive difference to the survival of the species.
We hope you enjoyed this article and found it interesting.
Do you have thoughts or questions for us? We would love to hear them? Leave us a comment below.
And for more hedgehog reading check out our full library here.