Beyond 4 wolves in a chase, success falls because of “free riders-“
The idea that big wolf packs menace elk more than small ones when it comes to killing them just isn’t so according to a new study of Yellowstone wolves. Researchers found that hunting success falls beyond 4 wolves not because wolves get in the way, but because some of the wolves put in a half hearted effort in the dangerous task. They do share in the rewards of their hunt, however. This behavior is called “free riding” by social scientists who study human behavior. Researchers also found that non-breeding wolves, the less adept hunters in the hunting party, and those who might have to perform an especially dangerous task tend to hang back.
These findings are also completely contrary to the notion that wolves are killing machines that hunt for the sheer joy of killing.
Abstract: “Nonlinear effects of group size on the success of wolves hunting elk.” Behavioral Ecology. November-December 2011 .
Daniel R. MacNultya,
Douglas W. Smith,
L. David Mech,
John A. Vucetich and
Craig Packer
Comments
Ralph, critical point here about the results: The abstract states TWICE that “success leveled off” at hunting party sizes above 4 wolves. It also states that “success does not increase across large group sizes.” It’s not the case that success “falls” as the post states.
This is important because larger packs obviously have more mouths to feed. Larger pack/hunting party size doesn’t lead to DECREASED aggregate success for the pack, but it does mean that each wolf is going to get a smaller share of what they do kill.
Which may mean that they have to kill more frequently to get what they need. There could be important implications for wolf management.
If aggregate success actually fell in groups larger than four, we might expect to seldom see groups larger than four because hunting in larger groups would be very clearly maladaptive — a downward spiral of lowered success, lowered food intake, lowered performance in subsequent hunts.
SAP,
“Larger pack/hunting party size doesn’t lead to DECREASED aggregate success for the pack, but it does mean that each wolf is going to get a smaller share of what they do kill.”
Not necessarily. Smaller packs loose more to scavengers such as ravens, eagles, and coyotes. Larger packs are busy eating, and helping keep the scavengers away. Ravens can consume an enormous amount of meat in a very short time. Lots of visual evidence of this and supported by section of Bob Hayes book Wolves Of The Yukon.
Excellent point Immer! Hunting success and meat per wolf are definitely two different things — bringing the prey animal down versus successfully converting it to energy.
So, with hunting success “leveling off” beyond four wolves, yet more wolves to deter other competitors once the prey animal is down, larger pack/hunting group size may be a toss-up, adaptively. Good point.
Beyond that, I’d say we can’t really generalize a great deal — a lot will depend on context (abundance of competitors, for instance) and idiosyncrasies of wolves and wolf packs.
SAP,
Yes the abstract did say that. Fortunately, I have a copy of the actual paper. Killing the prey didn’t just level off after 4 wolves, it fell quite abruptly.
The likelihood that the group of wolves would attack an elk they encountered dropped off more slowly when the group’s size was greater than 4.
Regarding your other comment. I know that large wolf packs often break into several hunting parties which are hunting more or less at the same time.
Ralph – thanks for the clarification. Also, I didn’t mean to imply that I knew something about wolf behavior that you didn’t. I very much doubt that’s the case. My apologies.
This is a fascinating topic overall – adaptive GROUP behavior is very interesting. So you’ve got free-riding wolves in the hunting groups: how do the non-free-riders deal with that? It’s not like they’re going to review the game film and find out who was slacking. They may detect the slackers in some way, but the question of how they would deal with them is very intriguing . . .
SAP:
Seems we had the same thought. I wonder if hierarchies are more rigidly enforced in large packs, or if dispersers tend to leave earlier? (Just thinking aloud). Wondering how wolves make “free-riding” work…???
Pups/young of the year might not do much except chase.
Hi all,
without reading the actual paper yet, a wolf pack is generally an extended family of an unrelated pair (the alphas) and offspring (pups, yearlings) of diff’ ages – usually 1-3 year old. Thus, even though there is a lot of free riding in larger packs, there is still the inclusive fitness hypothesis where not only do larger wolf packs convert prey into wolf (rather than scavenger) biomass, but also the wolves doing the killing are usually providing for related animals – so it isn’t all for not.
Makes one wonder how wolves ever “managed” to get by on their own (for centuries) without all this scientific input……….
Question – its been documented for years that the wolf’s “little canine brother” (coyotes) have done far more damage to livestock, so I’m curious to know, is anyone currently tracking depredations by coyotes when wolves are around?
Regarding the tracking of depredations by coyotes when wolves are around, this publication may have some relevance: http://www.aphis.usda.gov/wildlife_damage/nwrc/publications/09pubs/engeman099.pdf
Interesting, thanks Max. Did appear to be a drop in depredations by coyotes according to Fig. 4. Maybe the buzz words here should be better vigilence? “Future management” simply means continuing to kill the public’s wildlife, on public lands, to benefit private livestock raisers.
I wonder if this is why the super-size Druid Peak Pack splintered when it became so large. Makes sense.
“Free-riding” sounds to me like a bit of anthropomorphizing. Lets think about why a wolf might “free ride”: too inexperienced or young, wounded, too old or a bit sick; all spring quickly to mind. I didn’t read the report so maybe they tracked the same wolves over time to see repeated “free-riding” by the same wolves in situations where they could rule out those sorts of reasons I suggested.
Lets consider the obverse. Why would a wolf engage in “pay riding?” A chemical imbalance resulting in above normal adrenaline levels or some such or maybe it’s a requirement if you want to get voted in as an alpha member of the pack.
A new study using computer simulations would indicate:
Wolf Hunting Strategy Follows Simple Rules
http://www.physorg.com/news/2011-10-wolf-strategy-simple.html
1. Move toward prey until at a close but safe distance
2. Move away from other wolves also in position
Would seem to reinforce the research that smaller wolf packs hunt more effectively.
Yet, there can only be so many wolves around a particular prey animal at any one time due to prey size and terrain features. Perhaps this should all be rephrased as wolves that kill prey are more efficient when in smaller groups, as it is simply impossible for an entire wolf pack (if greater than 4) to be involved in the “kill.”
I’ve seen other research that would lean toward the kill being the product of one or two wolves.
+The results of the two studies raise questions about why wolves tend to live in packs, since the previously held assumptions of a large pack being more effective at hunting, and social behaviour and communication being essential, appear to be wrong+
Could it have to do with safety in numbers?
The same question could be asked about a pride of lions or African hunting dogs. Or, I seem to recall with wolves and African hunting dogs, members of the pack bring back and regurgitate food after a hunt for pups to young to travel. Bigger the pack – more insurance of food for growing pups.
Nancy,
I still look at it as only so many can get in on the “kill” process or they get in each other’s way. Pack is basically a family unit. Parents/ year old + non-dispersers and pups of the year.
The chase process can hold a few more, but the pack all but has to have “free riders” if over 4 wolves, and the average wolf pack size will vary as per the time of the year.
Yeah, understand only so many can get in on the actual “kill” process Immer. I’m just trying to relate to why it comes into play, when it comes to the reasons behind pack numbers.