Wolves Start Getting Old at 2

Agate pack breeder 113M (Mark Miller photography)

A wolf has a brief moment in the sun; by two years of age their physical faculties begin to wane and by 3 it’s all downhill.

The physical decline that comes with age varies among species. For an animal that is slow to mature (e.g. human & elephant), senescence begins late and it is a long gradual process. The general observation is that the faster an animal achieves physical maturity the sooner it starts on its path to senescence.

For the wolf, an animal that achieves sexual maturity quickly and experiences high fecundity, senescence comes fast and early.

Calling upon previous work (McNulty 2007) the authors focused on three of the most physically demanding aspects of the hunt “corresponding to the transitions between four behaviours that comprise the typical predatory sequence of cursorial carnivores hunting ungulate prey.”2

McNulty et al 2007

  • Attacking : running after prey; requires neither speed nor strength
  • Selecting: separating out an individual; requires burst of speed
  • Killing: grabbing, holding and overpowering prey; requires strength

The authors posited that physical decline in the wolf should be mirrored in each of the hunting phases and predicted the sharpest for the most difficult task. Ultimately, it’s expected to reduce their hunting success and it would also result in increased mortality risk.

Summary

  • Long-term study of wolves at Yellowstone National Park (YNP), 1995-2007
  • 94 identifiable individuals of known age
  • 469 wolf-elk encounters were observed, 394 of those involved groups of elk.
  • Individual wolves were scored for their successful participation in each predatory task

Findings

The findings are best explained with the 4 graphs above.

We can clearly see in graphs (a-c) that for each task a maximum is reached. The second and more telling pattern is the rate of decline following each maximum. The steepest drop observed the hardest task – selecting. The authors calculated the rate of decline:

“For each year beyond the onset of decline, individual ability decreased by 31% (P = 0.001), 17% (P = 0.032), and 10% (P = 0.013) in selecting, killing, and attacking, respectively.” 

The last graph (d) shows the overall probability of hunting success for a given an elk encounter. Based on various parameters the authors concluded that the increase or decline in P(h) was associated with increased or lack of inhibition while hunting but rather physical decline. It looks like old wolves are just as uninhibited in their twilight years as they are in their youth.

“We found little evidence that declining predatory performance reflected heightened caution with age rather than physical deterioration.”

“Taken together, these results suggest that age-related declines in predatory performance were not attributable to an elevated aversion to the risk of injury among older wolves.””Overall, the data paints a picture of the wolf as leading a fast life, maturing and reproducing many litters quickly before the onset of physical decline. 

It’s Not All Bad News. Even Wolves Subsidize their Elderly

However, the time lags between reduced overall performance (age 3) and accelerated mortality (age 5) and median life span (age 6) were not small. This might be the result of wolf social behaviour. Wolf packs are family groups that feed communally, so it is possible that younger hunters subsidized the survival of older, senescent (> 3.0-year old) hunters.” [1]

Having the youngsters pitch in for the older folk works even among wolves.

The story of YNP wolf 113M is a compelling case for the social welfare system among wolves. 113M was born in 1997 to 12F who tragically died 3 months later that year. Another female (33F) aided in the raising of the pups. In 2002 (past his hunting prime) 113M established his pack and went on to sire litters for 5 seasons. One of his sons eventually took over breeding duties for the Agate pack. 113M died at the age of 10 and was likely killed by a rival pack.

Aging 113M bring up the rear and killing all notions that pack leaders walk in front of everyone.

 

REFERENCES

1.  MacNulty DR, Mech LD, Smith DW (2007).  A Proposed Ethogram of Large-Carnivore Predatory Behavior, Exemplified by the Wolf. USGS Northern Prairie Wildlife Research Center. Paper 105. http://digitalcommons.unl.edu/usgsnpwrc/105

2.  MacNulty DR, Douglas DW, Vucetich JA, Mech LD,  Stahler DR, Packer C (2009). Predatory senescence in ageing wolves. Ecology Letters, (2009) 12: 1-10.  doi: 10.1111/j.1461-0248.2009.01385.x

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