How viper behavior increases their effect on prey populations

The sound of domestic cats fighting is probably familiar to most readers of this blog. Like most predators, cats defend their turf and the resources within. Prey is often scarce and starvation a real possibility, so it makes sense to fight for access to these resources.

But even amongst those who spend their lives observing vipers, it is rare to see a snake fight. Why? Unlike most predators, vipers are not territorial, only males fight, and only for access to females.

A pair of male western diamond-backed rattlesnakes in combat over an unseen female. For more on rattlesnake combat (including videos!), click on the image.

Vipers don’t need to eat as often as similar-sized, endothermic (warm-blooded) predators; they can go weeks or even months without food, while many birds and mammals eat daily. If prey is not limiting, why waste energy fighting over it?

But not only may vipers not view their neighbors as competitors, their presence may actually increase their hunting efficiency! Vipers use chemosensory cues to select hunting sites and preferentially choose sites where conspecifics (other members of their species) have been successful. We have also observed different viper species using the same hunting sites, so their presence may increase hunting effectiveness as well.

Another important resource for vipers (and other ectotherms) is an appropriate over-wintering shelter (den) and in some climates dens are a limiting resource. So vipers share; they den together.

Arizona black rattlesnakes at a communal den site in southern Arizona. Click on the image for the full story.

This behavior is not limited to conspecifics, vipers share their dens with other species too.

A Gila monster and western diamond-backed rattlesnakes share a den. Click on the image for more examples of sharing.

Vipers’ home ranges overlap with many conspecifics, as well as other snake species. Even male vipers tolerate others in their territory and outside the breeding season, encounters between them don’t usually end in a fight. Being good neighbors enables them to live in greater densities than mammal and bird predators.

In some cases, vipers may be 100-1000 times denser than their mammalian competitors!

But vipers need less food, so do these facts cancel each other out? Turns out they have a few other tricks up their sleeves.

Vipers can fast for long periods, so if prey populations crash, viper populations do not necessarily follow. Moreover since most vipers give birth every two to three years, prey population crashes may not have an immediate effect on their reproduction. When other predator populations have crashed (for example, classic predator-prey models like lynx and hares), and prey populations start to increase again, vipers are waiting for them.

Vipers can have a greater impact on prey populations than endothermic predators. So if your old attitude toward your viper neighbors was the only good snake is a dead snake, perhaps you’ll change your tune, to this one:

This post was largely inspired by the following article from Dr. Erika Nowak and colleagues:
Nowak, E. M., Theimer, T. C., and Schuett, G. W. 2008. Functional and numerical responses of predators: Where do vipers fit in the traditional paradigms? Biological Reviews 83:601-620.

Details about vipers (timber rattlesnakes) selecting hunting sites where others have been successful can be found here:
Clark, R. W. 2007. Public information for solitary foragers: timber rattlesnakes use conspecific chemical cues to select ambush sites. Behavioral Ecology 18:487-490.

Further Reading

Today’s post is part of #SnakesatyourService blog carnival. Want to find out more about ecosystem services offered by snakes?

In contrast to the story told here, some snakes are closely tied to their prey (frogs).

The Travelling Taxonomist discusses the ecological and cultural roles of snakes in Madagascar.

Still don’t want vipers for neighbors? Make friends with kingsnakes..

What is the role of snake sheds in the ecosystem?

While humans’ fear of snakes is irrational, for other animals it’s very real.

Big snakes also have a big impact.

The most famous example of snake’s impact on their ecosystem.

Finally, changing attitudes toward snakes in the next generation.