Why cause of death matters for wild animal welfare
September 23, 2020
This is the first post in a series. Read part two →
The most fundamental reason for viewing death as a bad thing is that it deprives individuals of future experiences, assuming those experiences would have been predominantly positive. However, the process of dying is also often painful in itself, and an individual’s death can have additional negative impacts—emotional and material—on others, including family and the broader population.
The costs of a death depend on its cause. Humans are willing to sacrifice periods of healthy life to avoid especially unpleasant deaths, and see various causes of death as more fearsome than others (Sunstein 1997; Chapple et al. 2006). Of course, people’s perception of how much suffering particular deaths would entail may be biased by things like squeamishness; they may assume that because a death is gruesome it must be especially painful. The terminal stages in the process of dying, during which suffering presumably outweighs pleasure, comprise a small fraction of most humans’ lives. Willingness to trade years of healthy life to obtain a quicker, less painful death implies that either the original manner of death must be extremely bad, or that we have an exaggerated sense of how bad dying is.
As recently as the 19th century, only around half of newborns could expect to survive to adulthood (Riley 2005). Many human cultures have had traditions of only conferring names on children when they reached a certain age, potentially because it was understood that most would not survive that long (but that if they did, they would have a decent prospect of reaching adulthood) (Lancy 2014). For example, birth registration was not a legal requirement in the United Kingdom until 1874 (ONS 2015). As average lifespan increases, the dying process represents an ever smaller proportion of human life.
While human childhood mortality has declined dramatically throughout much of the world, most wild animals still die at a young age relative to the longest-lived members of their own species (Figure 1). For these animals, the process of dying may actually represent a substantial portion of their lifetimes, suggesting that, in addition to knowing the most likely causes of death for entire populations, it would be especially valuable to know which manners of death are common among juveniles in specific wild animal populations.
Figure 1: A boxplot showing life expectancy as a percentage of a species’ maximum lifespan for 152 populations of fish (n=16), birds (n=54), mammals (n=72) and reptiles (n=10). Life expectancies were calculated from models found in the COMADRE database (Salguero-Gomez et al. 2016), and maximum lifespans were obtained from AnAge (De Magalhães et al. 2005). Across major vertebrate classes, most individuals live to only 10-30% of the age of the oldest known individuals of their species.
“Cause” of death can be interpreted in at least two different ways: “manner” of death, or “ultimate cause” of death. Both matter for wild animal welfare, but they can be difficult to disentangle in practice. For example, an animal who died during a forest fire may have died by burning or asphyxiation. Other animals may die in the immediate aftermath of a forest fire from dehydration or infected burn wounds. The welfare impact of these different manners of death would likely vary, and it is possible in theory to rank their welfare impacts based on the intensity and duration of suffering leading up to death (Figure 2; Sharp and Saunders 2011). Learning about the precise manner in which wild animals die can help us prioritize hazards to protect them from to reduce instances of the most extreme suffering. On the other hand, it is often easier to estimate the number of animals who died due to an ultimate cause - such as forest fires - than to break this down into specific manners of death. Learning about an ultimate cause of death, and the number of deaths resulting from it, is also useful for prioritizing welfare interventions directed at extending good lives.
Figure 2: An example scheme for grading the welfare impact of different manners of death, taking into account both the severity of suffering inflicted and the length of time it takes for the animal to die. Adapted from work by Sharp and Saunders (2011) on wild animal culling methods.
To minimize the suffering animals experience in the wild, we need to understand how and why wild animals die, paying particular attention to the most numerous experiences: that is, the deaths of juvenile animals belonging to common species. The rates of different causes of death are also valuable to know because even if dying turns out to be a minor contributor to lifetime welfare, or the difference in severity between manners of death is relatively low, substituting one manner of death for another less painful one could improve individual welfare without affecting population size, minimizing the number of variables we need to consider to determine whether an intervention is worth implementing.
In a series of posts to follow, I will review the methods available for studying causes of wild animal deaths and present a selection of published data on cause-specific mortality rates. Finally, I’ll describe some original modeling by former Wild Animal Initiative Intern Anthony DiGiovanni that explicitly considers how cause of death may change along with the size and demography of wild animal populations.
References
Sunstein, C. (1997). Bad deaths. Journal of Risk and Uncertainty, 14(3), 259-282.
Chapple, A., Ziebland, S., McPherson, A., & Herxheimer, A. (2006). What people close to death say about euthanasia and assisted suicide: a qualitative study. Journal of Medical Ethics, 32(12), 706-710.
Riley, J. C. (2005). Estimates of regional and global life expectancy, 1800–2001. Population and Development Review, 31(3), 537-543.
Lancy, D. (2014). “Babies aren’t persons”: A survey of delayed personhood. In H. Otto & H. Keller (Eds.), Different Faces of Attachment: Cultural Variations on a Universal Human Need (pp. 66-110). Cambridge: Cambridge University Press.
Office for National Statistics. (2015). How has life expectancy changed over time? Retrieved from https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/lifeexpectancies/articles/howhaslifeexpectancychangedovertime/2015-09-09.
Sharp, T., & Saunders, G. (2011). A model for assessing the relative humaneness of pest animal control methods. Canberra, Australia: Department of Agriculture, Fisheries and Forestry.
De Magalhaes, J. P., & Costa, J. (2009). A database of vertebrate longevity records and their relation to other life‐history traits. Journal of Evolutionary Biology, 22(8), 1770-1774.
Salguero‐Gómez, R., Jones, O. R., Archer, C. R., Bein, C., de Buhr, H., Farack, C., ... & Römer, G. (2016). COMADRE: a global database of animal demography. Journal of Animal Ecology, 85(2), 371-384.
