Weather is a major factor in determining whether animals can live and thrive in certain areas. Temperatures, in particular, dictate which animals can live in which regions. If temperatures are too low or too high, habitation by animals of certain species may prove to be impossible. Temperatures that are within the perfect range for some animals can prove deadly for others. In fact, fluctuations in temperature in specific areas sometimes result in the death of all the animals of a certain population in that place.
If weather conditions in certain areas are sufficient to maintain a population of animals, they will reproduce for generations until the conditions become unfavorable for survival. However, animals can survive in environments that make it possible for them to survive, but in which they are very uncomfortable.1
Let’s consider a scenario in which some animals can only survive if the temperature remains between 40ºF and 90ºF. If the temperature is within this range, the animals will continue to live and reproduce, although this does not necessarily mean that they will be living good lives. Small temperature differences, for example, between 55ºF and 75ºF, are unlikely to cause the animals too much discomfort. However, if the temperature fluctuates above or below that range, they might survive, but will experience suffering from the extreme heat and cold. The optimal situation for the wellbeing of the animals would be for them to only colonize areas in which they can live comfortably. Unfortunately, this situation is idealistic and far removed from the realities of nature.
In nature, the tendency is not to maximize happiness, but to maximize the transmission of genetic information. As a result, whenever it is feasible for a group of organisms to colonize a certain zone, it will most likely happen. Most wild animals have anywhere from dozens to millions of offspring, most of whom die shortly after coming into existence (see our page on population dynamics). If there isn’t space for them, the surviving animals will tend to colonize any space that is available even if conditions would cause suffering, since the alternative is to die. It is only necessary for a small number of animals to survive and reproduce in the harshest weather conditions in order for the population to continue. But the fact that some animals live long enough to reproduce does not mean that they are thriving or comfortable.
Adverse weather conditions can also reduce population numbers because animals tend to have fewer offspring when weather conditions are very harsh; however, this tends to have only a small effect.2 In addition, the populations of animals living in harsh weather conditions may eventually evolve so that they do not suffer as much. They may end up growing more or less hair, they may develop a different shape, or other changes may occur in their physiologies that improve their tolerance for the weather conditions. However, this takes many intermediary generations of suffering. Features such as being more or less furry prevail in a certain animal population because those who lack it are less likely to survive. After this happens through many generations, the features favoring survival become common in the population.
Many animals suffer due to changes in weather conditions that occur naturally. They may be fine during part of the year but experience great discomfort and hardship during a particularly hot summer or a cold winter. In temperate areas such as large parts of North America, Europe, and Asia, there can be big differences between the average, minimum, and maximum temperatures during the summer and the winter. Birds, reptiles, amphibians, and mammals who don’t hibernate have to endure huge variations in the temperatures they experience. The temperatures may be within the range they can stand, but far from comfortable for them.
Of course, humans would suffer similar discomfort if it weren’t for our ability to adapt to changes in temperature by wearing suitable clothing and using heating and cooling options as the seasons change. Nonhuman animals lack the technologies that we humans have at our disposal and, as a result, they can suffer greatly when weather conditions are extreme. When there are deadly heat waves that kill some humans in an area, there may be many other animals who also die due to the heat or complications from it, such as dehydration.3 In extreme cases, or when there are changes in the climate that occur progressively over longer time periods, whole populations may die off, suffering a great deal in the process. Animals dying from extreme weather conditions can experience a lot of pain in addition to losing their lives. However, it is worth noting that the number of deaths in a local extinction is not very different from the number of deaths that occur when populations thrive (which does not mean that the individuals thrive). If a pair of animals has thousands or millions of offspring and only a couple of them survive, the survival rate is only marginally better.
As mentioned above, the conditions that make an area suitable for an animal population to exist over time may be different from the conditions that make it possible for individual members of the population to survive. Most animals who are born in an area where conditions are unfavorable will die; only a tiny minority will survive. Animals sometimes also move into areas in which none of them can survive, and the population dies off in that area.
We might suppose that when all the members of an animal population die in a particular area, that area will never be populated by those animals again; however, animals tend to re-colonize the same areas over and over, and for the same reason, because conditions such as scarce resources force them to find a new place to live or they will die, usually due to starvation. This results in a continuous cycle of colonization, agony, massive death, and re-colonization.
This happens according to what biologists studying metapopulations call “the dynamics of sources and sinks.” A metapopulation is a group of populations of a certain species living in different areas. Often the animals of that species have the means to survive in some of those areas but not in others. Still, they keep colonizing the other areas they can’t survive in. They would become permanently extinct in those areas (the “sinks”) if it were not for the fact that they continually migrate to them from the other areas (the “sources”).
Animal populations are affected by many factors other than extremes of temperature. Some animals need a certain level of humidity to thrive and can suffer significantly in arid regions, even though they can survive. For others, it’s the other way around. Too much humidity or rain can also harm animals. Although there are many animals who are not affected by rain, or who actually like rain, there are others who are bothered by it or have illnesses or physical conditions that are worsened by it. Just as rain, snow, and strong wind can have a negative impact on our own wellbeing, they can cause similar discomfort and stress to animals living in the wild. Even if these uncomfortable weather conditions don’t kill them, just as they usually don’t kill us, they can still cause suffering for nonhuman animals.
Several other weather phenomena can have a huge impact on animals, and can wipe out entire populations. Their effects can combine with other limiting factors such as availability of food and water, presence of predators, and diseases. Consider, for instance, droughts, heavy snows, and floods. These extreme conditions can kill animals directly, for example by drowning, or indirectly, for example by damaging the food supply (to read more on this, see Animals in natural disasters). Weather conditions can also cause diseases in animals or trigger epidemics. Many animals, such as mammals1 and birds,2 are weakened during the winter due to the harsh weather, which makes them more vulnerable to becoming sick. Other animals suffer from diseases transmitted by flies that spread when certain weather conditions occur.4 Finally, in some cases, factors aren’t causally related, but combine in ways that harm animals. Animals struck by disease may be able to survive, but it may depend on the weather conditions in which they are fighting the disease, just as can happen with humans. If you didn’t have a house and clothes, you might be able to recover easily from the flu in the summer season, but it might be much harder for you to overcome it in the cold of a harsh winter. The same happens to animals in the wild. So we can see that weather conditions not only harm nonhuman animals directly, but can also be an important cause of indirect harm to animals in the wild.
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2 See for instance: Sasvari, L.; Hegyi, Z. (1993) “The effects of parental age and weather on breeding performance of colonial and solitary tree sparrow”, Acta Oecologica, 14, pp. 477-487; Bradley, M.; Johnstone, R.; Court, G., & Duncan, T. (1997) “Influence of weather on breeding success of peregrine falcons in the Arctic”, The Auk, 114, pp. 786-791.
3 This study found that “[a] brief but intense heat wave on 9 June 1979 caused catastrophic chick mortality in a population of Western Gulls on Santa Barbara Island, California, USA. Mortality ranged from 0 to 90% in different areas of the colony”: Salzman, A. G. (1982) “The selective importance of heat stress in gull nest location”, Ecology, 63, pp. 742-751. This has also been researched in animals used as resources; see for instance: Moeller, R. B. (2011) “Heat stress in cattle”, cetulare.ucanr.edu [accessed on 12 May 2013]. Rural Chemical Industries (Australia), Heat stress in livestock and poultry, heatstress.info [accessed on 21 June 2013]. Schoenian, S. (2010) “Heat stress in sheep and goats”, The Maryland Small Ruminant Page [accessed on 9 March 2013].
4 Henning, J.; Schnitzler, F. R.; Pfeiffer, D. U. & Davies, P. (2005) “Influence of weather conditions on fly abundance and its implications for transmission of rabbit haemorrhagic disease virus in the North Island of New Zealand”, Medical and Veterinary Entomology, 19, pp. 251-262.