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Posts Tagged ‘giant fox’

Alan Hepworth killed this 38-pound-fox was killed in Scotland. The size of a coyote, this fox was more than capable of killing lambs.

Remember when I suggested that one reason why British red foxes were getting larger is because they were no longer subjected to hunting pressures that select for foxes that are smaller in size?

Well, it turns out that I was wrong.

In fact, even my assumption that the foxes were evolving to be larger was erroneous.

It turns out that these giant foxes have very little to do with evolution in size and everything to do with increased nutrition.

The BBC reports that although there are some selective advantages for foxes to become larger it hasn’t really affected their evolution much. Different fox populations have varied in average size over the years, but the best prediction of how big foxes will grow is the amount of rainfall during the summer.

What?

Well, there is a little known fact about red foxes: they eat a lot of earthworms. David MacDonald, who extensively studied red fox foraging behavior near Oxford, found that one fox could eat as many as 146 worms in a single night.

This behavior has only been documented in European foxes. North American red foxes haven’t been seen going around eating lot of worms at night.

However, they don’t dig for worms.

Instead, they wait for a good spring or summer rain to bring them to the surfaces. When it rains hard, the worms come to the surface to mate, and we’ve all seen what happens when worms get caught on wet sidewalks. They usually flounder around for hours and then they die.

But in Europe, they are very likely to wind up in the belly of a badger or fox.

So when there is a very wet year, there are lots of worms coming to the surface, and the fox kits (which the Brits call “cubs” for some odd reason) are able to grow quite a bit larger than they normally would. Discussing this finding in that same BBC article, the authors point to a study that found rainfall was the important variable in determining how large a fox might grow:

Cubs growing up in areas that experience heavy rainfall in July tend to grow significantly larger than those that don’t.

“The difference between a dry summer and a wet summer is about 18% in body size,” says Prof Harris.

That is because heavy rainfall causes more earthworms to come to the surface. And earthworms are about the only prey that young foxes, unskilled at hunting, are able to catch and eat in the few weeks after they stop suckling from their mothers.

There is also no evidence to suggest that foxes are evolving to get bigger, though there are selective advantages about gaining large size:

A 2008 study in the Journal of Mammalogy,… by Carl Soulsbury and colleagues, found that heavier males hold larger territories and defend them better against their rivals.

This study, the first to show the affect of body mass in generally monogamous mammals, also revealed that heavier male foxes move over wider areas, and further from their territories. In doing so, they mate more with other females (known as extra-pair matings) and sire more offspring as a result.

So males at least do benefit from growing larger. Bigger females conversely do not appear to produce bigger litters.

So large sized foxes might be distributing genes for larger size in the fox population.

But it assumes that these foxes are larger because of some genetic variation.

In the end, the bulk of the evidence suggests that red foxes that reach larger size because increased nutrition from farm fields and from worms allows them to reach the larger size that many of them could reach if they were given similarly rich diets.

There is even less evidence that any size changes are truly adaptive; that the genes of carnivores such as foxes are evolving to produce bigger foxes.

More likely is that occasional changes happen on an individual level.

Where large foxes are found, they are not evolving to become bigger, but rather they have simply had the chance to eat more as they are growing, either earthworms or food left out by people, filling out their genetic potential.

Big foxes, it seems, happen to be normal foxes that have eaten a lot, not freaks or the product of a new evolutionary trend. And they have likely occurred throughout history.

Now, there is evidence that coyotes in the Eastern parts of North America are getting larger, but that’s so they can become more effective predators of deer. These larger coyotes also have some wolf ancestry, and as these coyotes have evolved to hunt deer, the larger size and more powerful jaws they got from their wolf ancestors has had a major selective advantage.

Something similar could happen in England.

Currently, one of the most common deer species in England is an introduced species– Reeves’s muntjac. Like all muntjac, it’s not a particularly large deer, weighing only 20 to 40 pounds. Some of these very large foxes exceed 30 pounds in weight, and they might be able to prey upon these muntjac, though I have not found any evidence that they regularly hunt either muntjac adults or fawns.

If these foxes do start to prey upon muntjac, there will be an advantage to having larger size, just as having a larger size in Eastern coyotes allows them to more effectively hunt white-tailed deer.

And maybe then we could see an actual evolution of larger sized foxes in England.

And that would be really interesting.

So it’s a rich diet of worms, not evolution, that is making some British foxes larger.

But it could lead to larger size if these foxes start to target larger prey on a regular basis.

In that scenario, the foxes could grow quite large.

One could almost imagine foxes reaching the size of wolves.

But I need to keep my imagination at bay.

At least for now.

 

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A 35.5 pound fox! That’s the size of a typical coyote bitch in my part of the world.

Source.

Why are the foxes getting larger?

I would submit that they are simply evolving to fit a niche that has been left vacant when wolves were extirpated from the British Isles. Something very similar happened when wolves were killed off in the Eastern US, and Western coyotes wandered in. They grew larger in size to be more effective predators of deer.

I also think that fox hunting ban in Britain has had an effect.  The fox hunts always exerted upon foxes a relatively strong selection pressure to remain small. If a fox is small enough, it can fit into the narrowest places and avoid the hounds. With the hunting ban, there is no longer much of a selection pressure to remain small.  A larger fox that exists hounds hunting it has certain advantages in obtaining access vixens and good hunting territory, and its prey choices become wider. A fox of that size might be a threat to some of the smaller deer species– and it certainly would be able to take relatively large lambs.

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From The Telegraph:

The male fox weighed two stone or 26.5lb and was four foot long, about the height of a seven-year-old child.

The giant fox was captured and killed in Maidstone after a cat in the local neighbourhood was killed.

It was trapped in a cage and put down in a humane way by Keith Talbot, a local vet.

He said foxes had been seen around his parents house days after their 19-year-old tabby cat was found killed on the doorstep.

Zoologists and experts said foxes said foxes could be growing bigger because of ‘easy pickings’ of food scraps in dust bins or even left out by animal lovers.

A dog fox will often grow bigger than the rest of the pack because the social system means the alpha male gets most of the food and the rest get leftovers.

There are thought to be at least 34,000 urban foxes in Britain.

Recently there has been concerns the animals could pose a threat after twins Isabella and Lola Kouparis were attacked in their beds in London.

However animal rights campaigners point out that most foxes live on insects and small mammals and pose no harm to humans unless they are frightened.

The Field Sports Channel is offering £100 for the best story of the largest fox. One taker has come forward with claims he shot a fox weighting 34lb in 2009, although this has not been confirmed with photographic evidence.

I guess the English have adopted one of our customs. In the US, there are coyote killing competitions. In the West, these competitions are about seeing who can kill the most coyotes within a given amount of time. In the East, where big coyotes are legendary, the goal is to see who can kill the biggest one. Anyone who kills a black, white, or otherwise unusually colored individual also gets plaudits. (Remember, the ones in the East have some wolf ancestry.)

Another reason why these foxes could be getting larger is that they have virtually no predation. Wolves no longer exist in England, and fox hunting has been banned. That means that foxes now exist at higher densities than they once did, and it may be that foxes that are bigger and tougher are better at competing for both vixens and food resources than smaller ones. With all of these foxes living in relative proximity to each other, it may be that a dog fox that has some size advantage might be better able to spread his genes, simply by muscling his way around smaller individuals.

And access to food would also play a role.  These foxes now have the nutrition to reach larger sizes.

The fact that this fox was killed in town means that he likely had access to really good nutrition his entire life. His ancestors may have been working their way towards the larger size as I describe may become possible when foxes exist at high densities.

Red foxes do vary quite a bit in size. A 26 to 34 pound fox is much larger than any fox around here. It actually would put  them in the same class as the smallest of coyote bitches.

Now, I’ve never seen one in North America of this size, but I did see one last week.

It was a taxidermied specimen at the German Hunting and Fishing Museum (Deutsches Jagd- und Fischereimuseum). I was shocked at how large this fox was. It was the size of a beagle.

Where I live, red and gray foxes are about the same size– 8-12 pounds. Virtually all red foxes here are derived from English imports to Maryland and Virginia in the seventeenth and eighteenth centuries. Genetically and morphologically, they are almost exactly the same as those foxes in England. Of course, there was a small native population of red foxes that lived in what is now the eastern US, but they were not that common before European settlement. (However, they did exist in Virginia during the Pleistocene).

The ones here also have very distinct black legs, which this particular fox does not have. Only its feet are black.

With 45 different subspecies of red fox,  we should see lots of variance between them. Not only do they come in several distinct phases in the wild, they also vary quite a bit in terms of size.

As wild dogs go, they are the true inheritors of the wolf’s empire. They are now more widely distributed than any other wild carnivore. Not only do they still maintain a vast Holarctic range, that also includes the Nile Valley, they are also found in Australia. Like wolves, they have the ability to rapidly respond to selective pressures and change their morphology and behavior to fit new ecosystems and new niches.

Large size may be of some advantage for certain populations, and that is probably the main reason why giant foxes are starting to appear in different European countries.

But if that readily available food supply disappears and the foxes find themselves suffering from both competition and predation from other animals, the large size may not be quite so advantageous.

 

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