Is it true that culling will cause deer to increase their reproductive output, resulting in an increase in deer?
Is it true that culling will cause deer to increase their reproductive output, resulting in an increase in deer?
People often question whether reducing the number of deer will actually lead to an increase in the deer population over time through increased reproduction. The phenomenon that is being questioned here is called compensatory reproduction. This is reproductive rebound effect that has been well-documented in some carnivore species, such as coyotes and jackals. It occurs as a result of changes to social structure that occur when when populations are reduced through hunting. In these species, young animals - even those that are biologically able to reproduce - typically do not because they do not have a high enough social rank to mate. When the social structure is disrupted by hunting, these young animals are able to advance their positions prematurely and begin breeding earlier in life. In addition, these species also may show increased litter sizes at younger ages. Compensatory reproduction has been a subject of great consideration in situations where carnivore populations are managed through lethal control measures (Minnie et al., 2016; Kilgo et al., 2017).
There is little evidence that suburban White-tailed Deer demonstrate true compensatory reproduction. This is because their reproduction in early years does not depend on their social structure. Doe fawns often breed in their first year, and the degree to which this happens is an important metric for understanding nutrition levels in the population (DeYoung, 2011). As with all species, it is possible that after an initial population reduction (such as after a culling effort), there may be more food available for fewer animals. This can result in what are called density-dependent effects. These effects can include a higher number of viable births and overall increases in offspring survival, as well as decreases in adult mortality due to decreased competition for food. These effects can be found in any animal population that is limited by resource abundance, and overcoming these effects is often an important consideration in setting hunting quotas or cull rates for animals.
Several studies have shown that these density-dependent effects can impact the results of efforts to reduce deer populations under certain conditions. This has most often been observed in populations managed through traditional hunting models - specifically in cases where hunter numbers are low or hunters show a preference for taking antlered animals. In environments (like suburban neighborhoods) where food is likely not a major limiting factor on deer populations, density-dependent effects tend to be relatively low. These effects, however, should be considered when setting annual goals for deer culls to reduce populations. It is essential for success that cull rates be high enough to overcome these slight increases in reproductive success (Giles and Findlay, 2004; Killmaster et al., 2009; Simard et al., 2013).
So what does this mean for controlling deer populations?
To reduce deer populations through lethal control (culling), initially a large number of deer must be removed from the population. This typically needs to be repeated annually for at least several years to achieve a substantial reduction in deer numbers. Over time, the number of deer taken annually can typically be reduced to maintain the population at this lower size. If culling is discontinued, the deer population will eventually return to its previous, larger size.
References:
DeYoung, C.A. 2011. Population Dynamics. In: Hewitt, D.G. (ed.). 2011. Biology and Management of White-tailed Deer. CRC Press, Boca Raton, FL. pp. 251-286.
Giles, B.G. and C.S. Findlay. 2004. Effectiveness of a Selective Harvest System in Regulating Deer Populations in Ontario. Journal of Wildlife Management 68(2): 266-277. Accessed at https://doi.org/10.2193/0022-541X(2004)068[0266:EOASHS]2.0.CO;2
Kilgo, J.C., C.E. Shaw, M. Vukovich, M.J. Conroy, and C. Ruth. 2017. Reproductive Characteristics of a Coyote Population Before and During Exploitation. Journal of Wildlife Management 81(8): 1386-1393. Accessed at https://wildlife.onlinelibrary.wiley.com/doi/abs/10.1002/jwmg.21329
Killmaster, C.H., D.A. Osborn, R.J.Warren, and K.V. Miller. 2007. Deer and Understory Plant Responses to a Large-Scale Herd Reduction on a Georgia State Park. Natural Areas Journal 27(2): 161-168. Accessed at https://doi.org/10.3375/0885-8608(2007)27[161:DAUPRT]2.0.CO;2
Minnie, L., A. Gaylard, and G.I.H. Kerley. 2016. Compensatory Life-history Responses of a Mesopredator may Undermine Carnivore Management Efforts. Journal of Applied Ecology 53: 379-387. Accessed at https://www.jstor.org/stable/pdf/43869390.pdf?casa_token=p-CaNUcChLoAAAAA:vhYJ5isaRVaDq3ZmOuZp_lQz-D-lYRyhKaxebjQdKd5P6JBqMpaeGWXbKPYcExjP4tG2Bj_YSPns8eKQ5pvU__Vm0sP0XnErsikL00uvI_RZEMqwlq4e
Simard, M.A., C. Dussault, J. Huot, and S.D. Côté. 2013. Is hunting an effective tool to control overabundant deer? A test using an experimental approach. Journal of Wildlife Management 77(2): 254-269. Accessed at https://wildlife.onlinelibrary.wiley.com/doi/abs/10.1002/jwmg.477