T'is a hard life....

[Hedgehoggy]

....having to fatten up for hibernation!



These juvenile siblings arrived this morning soooo very hungry and after a feed they fell fast asleep outside their nest box (my movements with the camera briefly woke them up, but they didn’t budge and just returned to slumber afterwards ).

[Farplace]

They look good. I currently dont have any hedgehogs in at the rescue, but I expect this to change any day - we usually over-winter quite a few undersized babies, and often a couple of adults needing extra care.

[Hedgehoggy]

Yep, the season for underweight juvs is on its way so get ready, or if you like, you can have some of mine!!

Amongst the usual juv hogs found out in the day searching for food, which just need fattening up, I’ve had two dog-attack hogs in recently. First one, juv male suffered nasty compound fracture and vet had to amputate his right rear leg. He's doing really well and is a delightful little boy to look after. Second one was fortunately a very large adult (with spines to match!) and suffered no physical damage, so she just needed observation, plenty of rest and good food before I soft-released her back into the wild. One consolation for big lady hog is that the dog in question apparently came off worse after the attack and was nursing a very, very sore mouth!

Thankfully, in both cases of these dog attacks, the owners were caring and compassionate to rescue the hogs from their dog's jaws and seek urgent veterinary help .

[Littlesparrow]

Do you know what causes hedgehogs to be underweight, are they a second late brood?

[Hedgehoggy]

Yes, they are indeed - known as 'autumn juvs' and are born September through to December in some parts of the country. Seeing as hedgehogs have been around a cool 15 million years, you’d think they would have evolved by now not to have this second late litter

[mbaldw]

Originally Posted by Hedgehoggy

Seeing as hedgehogs have been around a cool 15 million years, you’d think they would have evolved by now not to have this second late litter

Evolution has no plan or goal. In order for something to be gained or lost through evolution, two critical boxes must be ticked:

1. There must be the heritable variation to permit the elimination. In this case, some of the population must have a genome that instructs them to skip reproducing after a certain time in the year in favour of, say, eating to lay down fat for hibernation.

2. Differential mortality in response to a selective dis/advantage. In other words, producing a single litter early in the year (early breeders) should be more advantageous than the current multiple litter (late breeders) strategy, such that late breeders are less likely to survive to pass on their 'late' gene(s) than the early breeders (put simply, early breeders are 'fitter' than late breeders).

That we don’t see a shift away from a late litter suggests either there is no alternative currently at large in the population, or that an alternative does exist but is no more or less viable (in terms of survival to reproduction) than the ‘late’ gene.

Given that many of these ‘autumn orphans’ represent a second litter, I suspect there’s a fairly straightforward explanation. I think there’s probably a gene (or series of genes) that simply instructs its host to breed as often as it can, be that early or late in the season. I see this as a kind of 'spray-and-pray' approach where the possibility of more of your genes getting into the next generation is a better bet than the certainty of no more making it through. It’s like not putting all your eggs in one basket (or all your genes in one litter). After all, even if only one of the second litter survives, it’s still one more carrying part of your genome than if you hadn’t tried at all. Even if having a late litter meant the mother died of starvation during hibernation, if the first litter was born during the summer -- and are now fully weaned and happily laying down fat -- and if they survive hibernation, there’s a good chance they’ll pass the ‘spray-and-pray’ gene(s) on to future generations anyway – thus keeping it in circulation. Only if the late litter gene(s) somehow made it less likely the hoglets would live through hibernation to reproduce the following year would it be selected against.

The other point, of course, is that -- even if there were genes specifically for having early or late litters -- with more caring people devoting their time, energy and money to helping these late starters (and their mothers, if necessary) make it through winter, there's even less of a selection against late litters.

I don’t think I’ve explained that particularly well, but I hope you get the general idea!

Cheers,
Marc.

[Hedgehoggy]

Thanks muchly for the detailed explanation, Marc.

I fully understand the rationalisations set out in your post, especially the rationale for genes to spray-and-pray, and I appreciate evolution doesn’t happen overnight, but(!) I still feel late breeding in hedgehogs is detrimental, both for the offspring and their mother, to make it truly viable.

In essence, without researching further, I know of no other animal which puts its existence at high risk by leaving it until the 11th hour to breed without contemplating the impending effects of environmental factors such as winter climates, food availability (much of their natural food also hibernates over winter), and their imminent hibernation - of which they need to weigh at least 600g to survive hibernation and post-hibernation.

As an example, some birds (e.g. Blackbirds) will cram as many clutches into their breeding season as they possibly can in their approach to spray-and-pray, BUT they’re genetically programmed to know their viable cut-off time limit.

Originally Posted by mbaldw

The other point, of course, is that -- even if there were genes specifically for having early or late litters -- with more caring people devoting their time, energy and money to helping these late starters (and their mothers, if necessary) make it through winter, there's even less of a selection against late litters.

Eeek! Now finds herself in a hard place between two rocks if she’s impeding an evolution shift!

[mbaldw]

I know of no other animal which puts its existence at high risk by leaving it until the 11th hour to breed without contemplating the impending effects of environmental factors such as winter climates, food availability (much of their natural food also hibernates over winter), and their imminent hibernation - of which they need to weigh at least 600g to survive hibernation and post-hibernation.

I agree that it’s not a good situation for the hedgehogs, although I suspect there would need to be a gene to ‘switch-off’ their reproductive system a set number of days after arousing from hibernation. I guess that such a gene doesn’t currently exist. It does make me wonder, however, how many late litters do survive hibernation and when any cut off point would be? Are any born in October likely to fatten up in time? Then there’s the influence of location – late litters born in relatively rich habitat (such as urban areas where a lot of people put down food) are probably more likely to make to their ideal weight than those in poorer habitat. Also, a mild wet autumn will provide more food for them than a hot, dry one. All these factors are unpredictable (almost stochastic) by nature, which can mean autumn litters born in one year are more viable than those born in the following year. When the ‘game’ is all about getting your genes into subsequent generations, this moves the goal posts, so to speak.

One final thought is that if there was a cut off point for breeding and a female lost her litter, or couldn’t find a mate early in the season, she may end up not breeding at all. I wonder if this would still drive the population in the same direction as if she’d had a late litter with even only a 20% chance of survival? A lot of questions and I’m not expecting answers; I’m just thinking out loud.

Eeek! Now finds herself in a hard place between two rocks if she’s impeding an evolution shift!

I wouldn’t be too concerned if I were you. If the first litter are born early and survive hibernation, they’ll be carrying the ‘s-and-p’ gene through to the following generation regardless of you helping out late litters. As you’ve mentioned, being in a late litter generally isn’t beneficial to their survival so they need all the help they can get. I personally have no qualms about leaving food out for the hedgehogs that visit my garden (two at the moment, looking pretty healthy). Remember, the alternative to adaptation is extinction!

In other words...keep up the good work!

Cheers,
Marc.

[Hedgehoggy]

Some good points and observations, Marc

Originally Posted by mbaldw

Are any born in October likely to fatten up in time?

Those born in September stand a better chance, especially as you’ve mentioned above, if the climate is mild so they’re not having to burn up precious calories to keep warm, and/or they’re born in relatively rich habitat and being supplementary fed, so may just scrape through winter by the skin of their teeth.

Litters born in October are very unlikely to survive the winter. For example, even if a litter was born at the beginning of October, once fully weaned approx 6 wks later weighing approx 250g , it will be mid-November by the time they’ll disperse from the natal nest and fend for themselves. This doesn’t leave enough time to fatten up and they will also be burning up precious calories just trying to keep warm.

(It’s often a race against time for juveniles taken into care in October, with warmth and food on tap, to get them to a safe hibernation weight to be released on a mild winter’s day, providing there are no setbacks (e.g. heavy parasite burden, which the majority of autumn litters are afflicted with, compared with summer litters), otherwise those which don’t reach a good weight in time are over-wintered in care and released in the spring.)

Litters born in November and December (which some are ) will almost certainly perish, along with their mother if she hasn’t stored enough fat*. Just because a hedgehog looks large enough to survive hibernation, doesn’t necessarily mean it weighs enough for its size.

*Hedgehogs have large deposits of brown fat in addition to white fat. The white fat, which can account for 1/3 of body weight just before hibernation, provides the constant energy supply to fuel metabolism during hibernation while brown fat is most important for heat generation during arousals from hibernation. If fat stores are insufficient then the hedgehog will not survive hibernation.

Originally Posted by mbaldw

One final thought is that if there was a cut off point for breeding and a female lost her litter, or couldn’t find a mate early in the season, she may end up not breeding at all. I wonder if this would still drive the population in the same direction as if she’d had a late litter with even only a 20% chance of survival? A lot of questions and I’m not expecting answers; I’m just thinking out loud.

Mmm, good point and definitely food for thought, but the consolation of that scenario would be no autumn juvs (and possibly their mother) perishing.

Originally Posted by mbaldw

I wouldn’t be too concerned if I were you. If the first litter are born early and survive hibernation, they’ll be carrying the ‘s-and-p’ gene through to the following generation regardless of you helping out late litters. As you’ve mentioned, being in a late litter generally isn’t beneficial to their survival so they need all the help they can get. I personally have no qualms about leaving food out for the hedgehogs that visit my garden (two at the moment, looking pretty healthy). Remember, the alternative to adaptation is extinction!

Don’t worry, I rather said that tongue-in-cheek, but it did get me thinking! Glad to hear your hogs decided to stay around – just proves that the way to a hedgehog’s heart is via how much brown fat he can deposit!!

[Hedgehoggy]

Originally Posted by Hedgehoggy

Litters born in October are very unlikely to survive the winter. For example, even if a litter was born at the beginning of October, once fully weaned approx 6 wks later weighing approx 250g , it will be mid-November by the time they’ll disperse from the natal nest and fend for themselves. This doesn’t leave enough time to fatten up and they will also be burning up precious calories just trying to keep warm.

Tempted fate typing that sentence! Had two babies (not even juv status yet) brought to me on Thursday, found wandering about in a garden -144g & 167g respectively.

Posting photos as an indicator of size that these two would no way be able to gain sufficient weight before winter arrives (n.b. my hands are very small).



These two babies are loving the electric heatpad under their fleece,



but there was some serious huffing going on between them tonight and the smaller one had lost weight last night, so I may have to reluctantly separate them.