Hi Caroline –
It’s an interesting concept this “compensatory rebound effect.” I’ve E-mailed the columnist and editor, one I think is a wildlife biologist, of the Outdoors section of my local newspaper asking them to explain the concept; whether and how animal predators in the wild cause this effect; and if sport hunting does, and if so, can hunting be said to reduce or keep in check the deer herd and maintain quality habitat/deer. If I get an answer, shall come back and post.
In the meantime, I don’t find a definition of CRE or the concept discussed on pro-hunting and deer herd management websites. I don’t even see if nonhuman animal predation causes a rebound effect in deer. Is CRE a fact or a theory? Who coined the notion?
From some Q&As, CRE is explained as occurring when the population of deer is reduced and the remaining deer compensate by becoming more prolific by having more offspring. The term refers to a rapid or significant increase in deer after a sudden or accelerating decline, an increase to make up for the decline, but also it sounds like an increase over and above the numbers of deer before the decline produced by the hunt(s). CRE is the reproductive response of a species by which a **sudden** increase in food resources, due to a (usually) sudden decrease in the population, induces a high reproductive rate, sometimes over and above the original numbers. So, after a hunt the remaining deer benefit from enhanced food supply and so produce more deer (twins, sometimes even triplets) and reproduce at a younger age.
It is sometimes argued that CRE, in the sense of sudden population rebound or return to normal and/or above normal, properly only occurs among a deer herd that is initially unhealthy generally due to insufficient food because of really high deer numbers vis-à-vis available food resulting in an acceleration in their decline from malnutrition, starvation, disease, injury, etc., due to compromised health. So CRE really only occurs when densities of mature deer have gotten so high (because of no or very little predation by deer’s natural animal predators) and deer are becoming malnourished as a result and die off. Undernourished deer won’t give birth or give brith to fewer fawns because of the stresses they endure from unavailability of nutrition with increased deer density/competition for food, and their health becomes so compromised that they die off. As their numbers reduce, the habitat can better restore itself and then more food becomes available for the remaining deer. The healthier the deer, the more does will carry their fawns to term and more does likely to have twins, as normal, and does reproduce at a younger age as well. It seems that rebound applies only to stressed deer, maybe through wildlife mismanagement or outright ban in hunting, because deer densities are permitted to get overly high (because of no/limited predation by animals or efficient simulated predation by humans).
I’m not sure this kind of rebound effect occurs in nonhuman nature when there are sufficient predators to control deer. I see how different animal populations can bounce back: When the supply of food (animal prey or plant feed) is abundant, the more animals (predator and prey) can reproduce (the healthier the animal, the more likely it will reproduce); the less food the fewer numbers of animals. But, not sure if this is CRE in the sense of a significant increase after significant decline.
It’s obvious that between hunting seasons the deer population will bounce back. But, where is the research to show that hunting of healthy deer creates a rebound effect in the form of more deer than ever before, as implied by “AR”? It’s possible that after a season or two, surviving females might produce the number of offspring to replace those killed and some more so that the size of the herd increased from its original level. But is this reproductive rebound to the extent “AR” implies as over and above as to cause a deer population explosion, resulting in high DVAs, so many more bucks for hunters to hunt, etc. This kind of CRE wouldn’t really occur when a healthy herd is reduced. Deer densities can get high, but not to the point where deer become undernourished and sick, and then die off. So, hunting usually would kill healthy deer, the incremental healthy surplus. Healthy does will have 2, sometimes 3, offspring annually. There’s no reason why fertility rate among healthy does would significantly increase due to a reduced number of healthy deer. Their capacity to reproduce is max’d at 2 fawns, which is the norm (and sometimes triplets). Increased fertility can be genetic, too. But, the point being that, so long as a deer herd is not stressed from too few resources to sustain the population’s density, the reproductive rates are normal – generally twins – and so CRE doesn’t occur when deer numbers are reduced. Only under bad wildlife management would CRE occur, and, again, bad management does not prove hunting is a bad management tool.
Whatever, I still don’t see the problem even if hunting does cause CRE simply because keeping deer below the carrying capacity of available habitat = more high-quality habitat and increased nutrition per remaining deer = healthier does = more fawns = greater deer/buck harvest each year. So long as habitat and deer quality are maintained so deer aren’t malnourished or starving, what is the problem?
CRE doesn’t seem to prove that hunting can’t reduce or, rather, keep in check the size of rural wild deer populations. So long as habitat-deer quality are maintained. Even if the sudden, temporary reduction of hunting causes more food availability for deer who survive and increases their reproduction (‘rebound effect’), that is what happens in nonhuman nature predator-prey relationships. Rather like hunting, nature is also a ‘vicious cycle’ of killing and regeneration/rebound, where predators kill prey causing a boom in prey populations, then killing again, and so on.
Again, we’ve reduced or eliminated the predators (for our safety, not because of managed sport hunting) and we’ve dissected deer habitat and enabled deer to thrive by our own (non-hunting) land-use practices. Without animal predation, rural wild deer don’t die in the numbers and as quickly as they did by animal predation. Deer are able to live longer and die only over time; and in the meantime before they die they can cause a lot of habitat damage, affecting other critters. So, we have a choice: Letting nature take her course = fewer struggling, malnourished deer and degrading habitat that may not be able to restore itself. Or, allow annual managed hunting = healthy habitat and more healthy deer.
Now, if habitat is degraded because of deer density, but deer venture outside their habitat because of poor habitat or because sprawling human settlements, roads and parking lots destroy their resources, and then the deer are being boosted by food plots and supplemental feeding, that is a different matter. Again, you need to understand that food plots and supplemental feeding does not happen across the board. Also, states ban supplemental feeding or strongly discourage it, even where CWD has not been detected. However, my apologies for overlooking your acknowledging that supplemental feeding is banned or discouraged in some states. And, food plots won’t attract deer where surrounding habitat can already meet deer’s natural nutritional needs; its only when surrounding habitat is poor will they come, and they should not be had where deer can come into conflict with people and cars. I hardly think that food plots and supplemental feeding make a huge dent in the deer population increase. Feed plots and supplemental feeding have never been substitutes for other management tools that improve habitat, and quality deer, over larger rural areas. Again, too many deer soon will end future hunting because quantity will come at the expense of quality deer, which will reduce deer as well, then no hunting. Hunters want quality deer for quality meat, and quality racks. If hunting is all about more deer, bigger racks and good meat, why would they let deer herds explode to the point of reducing quality habitat and deer and limiting future hunting?
I may be able to agree with you regarding deer birth control for urban areas (“money and effort on Deer birth control for urban areas”). I’m glad you’re getting it: Making the distinction between urban deer and rural deer populations. Cervine birth control technology was developed and is designed to control only deer populations in urban/suburban areas where hunting is illegal and unsafe. Deer contraception is not a method to limit or end sport hunting of rural deer populations. Further on in your post, however, you regress by connecting sport hunting and IC deer birth control: “… profit from the sports hunting industry comes from whitetails they do not want to reduce the herd size in long term and that is why they reject IC deer birth control …” Caroline, Dr. Jay Kirkpatrick (your source) says that to connect the idea of contraceptive control of a small number of discrete deer populations to sport hunting is “irrational.”
So, if you refer to DVAs in city and urban communities, hunting isn’t allowed in such human-dense populated areas. DVAs continue to climb because these deer populations aren’t being controlled by acute mortality. And hunting has not caused these deer to move into urban areas to cause DVAs – people who want to build homes, shopping malls and roads on once-deer habitat and also want to have cars, as well as other land-use practices, are far more the cause of DVAs in urban/suburban areas than hunters and hunting. The quote on “hunters in the woods pushing deer out of wooded areas, making them run across the road,” tell me, did hunters create those roads in rural and urban areas and all the cars? Hunters, more than anyone, are about increasing and preserving habitat for wildlife; hunters don’t want to see roads, shopping plazas and parking lots and residential development dissecting habitat. Again, no, hunting should not be held accountable for human injuries/deaths from DVA on rural or urban roads, as explained already, but which you can’t refute.
I am also sounding like a broken record. So, I will bow out from further discussion of your question of hunting “producing deer if its about reduction,” the issues (very complex and multi-factorial) of which have been answered. I’ll still follow this thread to see if anything new comes up. I’m interested in Iowanic’s question on whether animal predators in the wild set off this rebound effect. And, I’m awaiting your answer to Iowanic’s question: What is the largest herd of deer on whom deer birth control has ben used?
Thanks for the conversation, Caroline, and Peace.
Carol Reeves out.