Beyond the Bars: Ethical Enclosures for Captive Animals (Part Three)

"Westland kassen". Licensed under CC BY 1.0 via Commons -

Climate-controlled greenhouses. (Photo source. CC by SA 1.0)


I’ve already discussed (in the previous article) ways to think about the amount of three-dimensional space an animal’s enclosure should have. The next consideration should be climate, both macro and micro.

Climate, as most of us know, is the general range of weather in an area: this can include average temperatures, humidity, precipitation, and sunlight. In terms of animal housing, climate refers not only to these things, but to ambient things such as noise, artificial light, and vibration.

You might think that climate would only apply to outdoor animal exhibits rather than those within temperature-controlled buildings, but this is incorrect. A pleasant indoor climate for humans is obviously not the ideal one for all animal species, and this needs to be taken into account when designing an enclosure. In fact, climate is one of the most important things to consider for any enclosure, more important than space, or enrichment, or social interaction. Why? Well, previously I talked about the difference between acute and chronic stressors. Housing an animal in a climate it is poorly adapted to is one of the greatest causes of chronic stress for animals in captivity, if not outright death.

Climate for animals in captivity can be divided into two parts: macroclimate and microclimate. The macroclimate is the general climate of the area at large: generally, it would be the weather with respect to animals in outdoor enclosures, and the climate of the building surrounding indoor enclosures. Ideally, the macroclimate will match the animal’s needs and no adjustments will have to be made to the microclimate. Of course, this doesn’t always happen.

Sometimes, even having the appropriate macroclimate isn’t enough due to the way animal enclosures are built. Glass aquariums have poor ventilation and will retain more heat, cold, and humidity compared to, say, a wire cage. This is great if you have an animal with high heat and humidity requirements, like a reptile, but not so great for a small mammal like a mouse. Not only will they find the lack of airflow stifling, but the smell of their feces and urine will be greatly magnified due to the higher humidity. I’ll discuss the benefits and drawbacks of different barrier materials in a later article, but for now let’s break down the different components of climate.


Speaking of humidity, this is an aspect of climate that many pet owners forget or neglect. But it is important for almost every group of animals- certainly for reptiles and amphibians, but also for insects, mammals, birds, and even fish. Yup, fully submerged fish can be affected by humidity! At higher humidities, water from aquariums will evaporate more slowly. Since surface evaporation causes cooling, aquariums at high humidities tend to have warmer water.

For mammals, high humidity causes the aforementioned issue with feces and urine that linger and stink up the air, but it’s not just the stink- it’s the increased likelihood of bacterial infection. Wetter bedding will also need to be changed more frequently. Conversely, extremely dry bedding due to low humidity is dustier and can cause irritation and respiratory infections.

These issues with dirty bedding also plague birds, and to a lesser extent reptiles and amphibians (cold-blooded animals are less frequent with their, er, eliminations than warm-blooded ones are). Amphibians obviously prefer to have wet skin, given that it is a breathing surface for them, so high humidity is generally a must- you don’t see many frogs in deserts or tundras! Reptiles require particularly high humidity when they are shedding their skin, because it can crack or become painful when too dry. Insects, too, need high humidity when shedding, and also because many of them quench their thirst using water suspended in the air.

Some animals, particularly reptiles, may appreciate the opportunity to visit areas of their enclosure with varying rates of humidity. These micro-micro climates can be as simple as plastic hideaways lined with moist bedding such as peat moss- a mini-sauna, if you will.

A leopard gecko enjoying this humidity hide. (Photo source.)

A leopard gecko enjoying a humidity hide. (Photo source.)

High humidity can contribute to heat stress in animals that sweat, such as cows, horses, and humans, as well as animals that pant, like dogs. Much like how an aquarium will be hotter if water can’t evaporate from the surface, animals that sweat or pant rely on moisture evaporating from the surface of their skin to cool them down. If the air is already saturated with water, sweating or panting becomes ineffective and the animals will overheat in high humidities at temperatures they might be comfortable at in low humidities.


Every animal species has what’s called a “thermoneutral zone.” This refers to the range of temperature where the animal’s metabolism works the most efficiently and no chemical or physical changes are needed to make it more comfortable (i.e., in the human thermoneutral zone we wouldn’t sweat or shiver). Being kept for long periods of time out of the thermoneutral zone is obviously quite stressful- the microclimate should always be kept within this range, except in special circumstances such as a mother with newborns who cannot maintain body heat as effectively as adults.

Ectothermic animals (i.e., cold-blooded animals) obviously need to be housed in microclimates with carefully managed temperatures. But mammals and birds are also sensitive to temperature, particularly tropical species. If a tropical animal is housed outdoors in a temperate climate, there needs to be a sufficiently warm indoor space for them to retreat to during the colder months. Likewise, if an animal adapted for extreme cold is being kept in a warmer climate, adjustments must be made. Some zoos feed their polar bears special diets so that they do not build up the insulating layer of fat that keeps them warm in Arctic regions.

The pet industry is most accommodating to reptiles as far as temperature adjustment devices go, with fish following as a close second. Yet many pet owners are under-educated about how to appropriately manage temperature. For many species (including our own) the difference of a few degrees can lead to great discomfort. Very rapid changes in temperature are also highly stressful, even if it’s a change from an inappropriate temperature to a more appropriate one. Heating and cooling should take place gradually, particularly for aquatic animals, which can go into temperature shock if too-hot or too-cold water is added to their tanks. Water temperature also affects how much dissolved oxygen is present, the types of filter bacteria, the toxicity of ammonia, et cetera, et cetera.

As with humidity, making areas with multiple ambient temperatures available for an animal can be highly beneficial, so long as they’re all in the thermoneutral zone. Again, reptiles in particular need varied temperature spots in order to micromanage their own body temperature- basking spots are important for initially raising body temperature, but the whole enclosure should not be basking temperature or the animal risks overheating. Having multiple ambient temperatures available may be particularly important for snakes, which use different temperatures for basking, resting, eating, digesting, and other activities that require different amounts of energy.

Experienced hobbyists encourage reptile owners to have not one but multiple thermometers placed throughout their enclosures in order to manage different temperature ‘strips’. Hides should be available in each area of different temperature as well so the animal does not have to flee to a too-hot or too-cold area in order to feel safe.

While access to multiple temperature zones is crucial for ectothermic animals, all animals may benefit from having the option to move to areas with different temperatures. Having the option to retreat under cool shade or into a warm den is critical for animals housed outdoors, and even animals housed indoors at a stable, comfortable temperature might prefer warmer temperatures while sleeping and/or cooler temperatures while active. This can be achieved fairly simply by creating ‘den’ areas lined with soft bedding as well as areas with strong airflow to generate cooler temperatures.

Cattle utilizing some artificial shade. (Photo source.)

Cattle utilizing some artificial shade. (Photo source.)

For species adapted to temperate environments, seasonal temperature variation will greatly affect behavior, and many animal caretakers try to mimic this (particularly for animals that use seasonal cues to breed). However, if the caretaker wants to imitate normal a seasonal cycle, they should be ready to facilitate other temperature-based changes, such as changes in coat, sleep, and most importantly, diet composition. Changes in temperature and photoperiod can greatly affect an animal’s metabolism. Speaking of photoperiod…


Humidity and temperature are, perhaps surprisingly, two of the most crucial factors to any captive animal’s welfare, but there is a third factor that often goes unnoticed or underappreciated: lighting. Light intensity and duration can actually have quite profound effects on both an animal’s behavior and their internal chemistry. It may make sense intuitively that too much light would bother a nocturnal or burrowing animal. But light can affect everything from metabolism to sex drive as well.

Let me go into a little more detail, since this science isn’t well known to many people. The photoperiod, or length of day, is what many animals instinctively use to determine what season it is. Longer days = summer, shorter days = winter, for example. For years, scientists and farmers have been able to manipulate photoperiods in order to make certain species hibernate or go into estrous. By the way, humans are affected by photoperiods as well, though exactly how is poorly understood.

Hours of day length by latitude and day of the year. "Hours of daylight vs latitude vs day of year cmglee" by Cmglee - Own work. Licensed under CC BY-SA 3.0 via Commons -

Day length by latitude and time of year. (Photo source. CC BY-SA 3.0)

Because so many animals undergo seasonal changes in body chemistry and behavior, light control is crucial to welfare, and applies mainly to animals in indoor enclosures who aren’t exposed to natural daylight. These animals should be subjected to the appropriate number of hours of light each day, and seasonal changes in photoperiods should be done gradually so that they have time to adjust. Note: it is extremely cruel to expose any animal to 24-hour-a-day lighting. This destroys their normal circadian rhythm and can lead to the refusal of food, inability to sleep, and even death. This goes for fish as well- I implore you to turn off the lights on your fishtank at night! The only exception to this would be for animals that live in polar regions during periods of 24-hour daylight.

Photoperiods aren’t the only welfare-relevant aspect of light. Like us, many animals are affected by the amount of ultraviolet light in the environment. Too much may give our sensitive skin burns or melanomas, but too little can also limit our body’s ability to manufacture vitamin D. Animals too use UV light to manufacture vitamins and to promote healthy bones- this is especially important for the development of delicate bird bones. When preening, birds actually spread a special oil secreted from a gland above their tail over their feathers. This oil reacts with sunlight to produce vitamin D, which the birds then consume during the next preening session. Birds kept in low-UV light enclosures are at increased risk for dull feathers, overgrown beak, wobbly legs, bone fractures, seizures, and a whole host of other health issues.

Reptiles have difficulty absorbing vitamin D through dietary changes and need UV light in their environment in order to synthesize it. Otherwise, they risk getting metabolic bone disease. Reptiles need both UVA (short-wavelength) and UVB (long-wavelength) light in order to stay healthy. (The one exception to this is snakes, who have evolved a different means of synthesizing calcium.)

A tortoise showing irregualr shell growth (pyramiding) due to low UV light exposure. "Gopherus agassizii - Buffalo Zoo" by Dave Pape - Own work. Licensed under Public Domain via Commons -

A tortoise showing irregular shell growth (pyramiding) due to low UV light exposure.

While the health of birds and reptiles crucially depends on the availability of UV light, it is important to remember that mammals benefit from it too. In fact, research is showing more and more that UV light exposure greatly affects the vitamin D levels of primates and rodents. Unfortunately, glass absorbs UVB wavelengths, so simply placing the cage near a window is not sufficient.

It is important to remember that even though exposure to UV light is required for the health of many animals, too much of it can be as bad for them as it is for us. Overzealous reptile owners can easily give their pets carcinomas if they aren’t careful about the composition of their light.

Beyond all the health benefits (and dangers), an animal keeper should note that birds, reptiles, amphibians, and even some mammals can actually see UV light, and providing it enables them to see certain colors in their environment. Many birds and reptiles have areas on their body that fluoresce in UV light that are used for signalling, and rodents that can see UV light use it to detect urine splashes while scent-marking.

Cockatiels and their eggs look dramatically different to the avian eye. (Photo by

Cockatiels and their eggs look dramatically different to the avian eye than the human eye. Left- human vision. Center- bird fluorescing under UV light. Right- simulated avian vision. (Image by Dr. Klaus Schmitt.)

Light intensity and shading is another factor to consider when designing animal enclosures. The intensity of the sunlight in the desert, for example, is likely greater than the intensity of the sunlight in the British countryside. Logically, it follows that animals from these different environments should be exposed to different light intensities. Animals that live in shaded forests are also more apt to prefer dappled and muted light than those from the open plains. Shadows will be comfortable for an animal like a rat, which depends upon them to hide in, compared to a meerkat, which seeks unshaded ground in order to watch for aerial predators. As ever: look to the wild behavior of an animal for answers.

Little shade present in the natural habitat of the meerkat.

There’s little shade present in the natural habitat of the meerkat. (Photo source. CC BY-SA 3.0)

Noise and Vibration

Keeping in mind that animals have different physiology than humans, we can’t assume that just because a noise is at a comfortable hearing level for us, it is safe for animals. Research suggests that noise over 85 decibels causes acute stress and can even damage the hearing of rodents and nonhuman primates. That’s about the loudness of a lawn mower.

Those aware of human limitations will note that hearing noises over 85 db for sustained periods isn’t particularly good for humans, either, and they’d be right. But animals such as rodents can also hear noises in frequencies we cannot, which makes it harder to control the noise in their environments. Much modern machinery, for example, consistently produces sounds in these frequencies, particularly video monitors.

Noise is an especially serious problem for animals exhibited in zoos. At peak traffic, zoo visitors can generate continuous noise of over 70 db, which is much louder than even the noisiest rainforest habitat. Unfortunately, the long-term effects of this on zoo animals are understudied, but what has been observed is that larger crowds increase vigilance, territoriality, and stress levels in many species. Some zoos are attempting to tackle this issue by launching campaigns to change visitor behavior or by adding sound-dampening material to habitats.

You probably expect to hear this by now, but noise levels do not just affect mammals and birds, but reptiles, amphibians, and aquatic animals as well. Snakes, despite their lack of external ears, can still pick up sound through vibrations that pass through their skull, through a single inner ear bone, and into the inner ear itself. This inner ear can still be damaged by excessive noise, so snake owners who like playing very loud music should take note of this.

Frogs appear not to have ears, but actually use the circular timpanic membranes located behind their eyes to hear with. "North-American-bullfrog1" by Carl D. Howe - Carl D. Howe, Stow, MA USA. Licensed under CC BY-SA 2.5 via Commons -

Frogs may appear not to have ears, but they actually use the circular tympanic membranes located behind their eyes to transmit sound waves to their inner ears. (Photo by Carl D. Howe. CC BY-SA 2.5)

Fish and fully-aquatic amphibians can also still hear, and are particularly sensitive to vibrations as well. (All sound, as a matter of fact, is simply rapid air vibration.) Given how noisy pumps, bubblers, and other underwater devices commonly used in tanks are, the effect of vibration and sound on aquatic animals is very understudied. Some preliminary studies suggest, unsurprisingly, that high, constant noise levels increase stress and weaken fish immune systems.

Noise pollution does not just lead to stress and hearing loss, however. It can also have a negative effect on signalling behaviors dependant on sound. Obviously, if a signal is hard to hear, it’s not going to be effective; this is why many studies have found that birds living near noisy roads tend to be extra-loud and extra-high-pitched. In many cases, animals also find constant noise distracting or frightening, which can further inhibit normal behaviors.

Of course, not all noise is bad- an absolutely silent environment would be nearly if not more cruel to keep an animal in than a very loud one. Environmental noise can function as positive enrichment when played at the appropriate levels. In fact, some studies suggest that soft music played during active hours actually promotes positive behaviors in laboratory animals and reduces stress. Elephants reduce stereotypic behavior when listening to classical music and dogs staying in veterinary hospitals show reduced stress responses when listening to someone play a harp. Cows produce more milk when listening to slow-tempo music than when listening to fast-tempo music.

One study on how music affected the behavior of members of a chimpanzee colony found that listening to music reduced aggressive and agitated behavior between individuals and increased prosocial behavior. Interestingly, it also correlated with a decrease in overall activity levels. The authors of the paper suggest that music is an effective way to calm animals during more stressful, active times of the day, but is better off not played during times of the day when the animals are already low-activity. As a side note, apparently these chimps particularly enjoyed a live concert from a classical orchestra.

Music may be effective in calming animals because it masks other, more stressful sounds. Allowing the animals to choose what sounds they hear can also be considered a form of enrichment. The authors of the chimpanzee study are already investing in ways to allow the chimps to pick which types of music they want to hear.

Auditory enrichment is not limited to just music. Many animal species contact their neighbors of the same species via long-distance calls, such as the wolf’s howl or the songbird’s song. By playing back these calls, zookeepers can induce captive animals to respond with their own calls as they would in the wild.

Sound can also be used in combination with other forms of enrichment- one of my favorite examples of this is one study where an author used recorded bird calls to induce predatory behavior in a leopard named Sabrina. Speakers with motion detectors were placed throughout her enclosure, so that when Sabrina located the source of one bird call, the next speaker would start playing- causing her to run and jump from area to area until the sounds finally led her to a food chute. If Sabrina didn’t trigger all the motion sensors and then reach the food chute fast enough, she wouldn’t get her treat. Essentially, what this all does is mimic natural hunting and foraging behavior: chase sound, get food. By running each part of this complex enrichment system on a random, varied schedule, the researchers kept Sabrina very well entertained for over a year and a half.


We don’t often think of climate as something that greatly affects our own health, but we, like every other animal, depend on certain temperatures, light levels, and humidity levels for our own survival. That we take most of these for granted is only because we have been able to engineer ideal indoor climates for ourselves. If animals are taken from their natural environment and placed somewhere that is the equivalent of plopping a naked human into the Sahara desert, there are obviously going to be consequences that we need to control for.

In terms of health, it is crucial to have an understanding and a means of replicating a captive animal’s ideal temperature, humidity, and light conditions within its enclosure. But this series of articles is about more than just physical health: it is about thriving, not just living. By offering animals choices and variation in all three of these aspects, as well as sound, we can greatly improve their mental health.

That’s about it for this article in the collection. Next time, we’ll hopefully get to talk about enclosure substrate, topography, shelters, barriers, and more!

Previously in this series:


Stress and Space

To view a complete listing of all the scientific articles I’ve written, check out my Nonfiction section.

References and Further Reading

Almazán‐Rueda, P., Van Helmond, A. T., Verreth, J. A. J., & Schrama, J. W. (2005). Photoperiod affects growth, behaviour and stress variables in Clarias gariepinus. Journal of Fish Biology, 67(4), 1029-1039.

Anderson, P. A., Berzins, I. K., Fogarty, F., Hamlin, H. J., & Guillette, L. J. (2011). Sound, stress, and seahorses: the consequences of a noisy environment to animal health. Aquaculture, 311(1), 129-138.

Bruintjes, R., & Radford, A. N. (2013). Context-dependent impacts of anthropogenic noise on individual and social behaviour in a cooperatively breeding fish. Animal Behaviour, 85(6), 1343-1349.

Chávez, A. E., Bozinovic, F., Peichl, L., & Palacios, A. G. (2003). Retinal spectral sensitivity, fur coloration, and urine reflectance in the genus Octodon (Rodentia): implications for visual ecology. Investigative Ophthalmology & Visual Science, 44(5), 2290-2296.

Dickinson, H. C., & Fa, J. E. (1997). Ultraviolet light and heat source selection in captive spiny-tailed iguanas (Oplurus cuvieri). Zoo Biology, 16(5), 391-401.

Emerson JA, Whittington JK, Allender MC, Mitchell MA. Effects of ultraviolet radiation produced from artificial lights on serum 25-hydroxyvitamin D concentration in captive domestic rabbits (Oryctolagus cuniculi). Am J Vet Res. April 2014, Vol. 75, No. 4 , 380-384

Ferguson, G. W., Brinker, A. M., Gehrmann, W. H., Bucklin, S. E., Baines, F. M., & Mackin, S. J. (2010). Voluntary exposure of some western‐hemisphere snake and lizard species to ultraviolet‐B radiation in the field: how much ultraviolet‐B should a lizard or snake receive in captivity?. Zoo biology, 29(3), 317-334.

Institute of Laboratory Animal Resources (US). Committee on Care, Use of Laboratory Animals, & National Institutes of Health (US). Division of Research Resources. (1985). Guide for the care and use of laboratory animals. National Academies.

Junge, R. E., Gannon, F. H., Porton, I., McAlister, W. H., & Whyte, M. P. (2000). Management and prevention of vitamin D deficiency rickets in captive-born juvenile chimpanzees (Pan troglodytes). Journal of Zoo and Wildlife Medicine, 31(3), 361-369.

Kendall, P. E., Nielsen, P. P., Webster, J. R., Verkerk, G. A., Littlejohn, R. P., & Matthews, L. R. (2006). The effects of providing shade to lactating dairy cows in a temperate climate. Livestock Science, 103(1), 148-157.

Kenny, D. E. (1999). The role of sunlight, artificial UV radiation and diet on bone health in zoo animals. In Biologic Effects of Light 1998 (pp. 111-119). Springer US.

Klaphake, E. (2010). A fresh look at metabolic bone diseases in reptiles and amphibians. Veterinary Clinics of North America: Exotic Animal Practice, 13(3), 375-392.

Kuiken, T., Fox, G. A., & Danesik, K. L. (1999). Bill malformations in double‐crested cormorants with low exposure to organochlorines. Environmental Toxicology and Chemistry, 18(12), 2908-2913.

Manser, C. E. (1996). Effects of lighting on the welfare of domestic poultry: a review. Animal Welfare, 5(4), 341-360.

Markowitz, H., Aday, C., & Gavazzi, A. (1995). Effectiveness of acoustic prey?: Environmental enrichment for a captive African leopard (Panthera pardus). Zoo Biology, 14(4), 371-379.

Oppedal, F., Juell, J. E., & Johansson, D. (2007). Thermo-and photoregulatory swimming behaviour of caged Atlantic salmon: implications for photoperiod management and fish welfare. Aquaculture, 265(1), 70-81.

Ortavant, R., Bocquier, F., Pelletier, J., Ravault, J. P., Thimonier, J., & Volland-Nail, P. (1988). Seasonality of reproduction in sheep and its control by photoperiod. Australian journal of biological sciences, 41(1), 69-86.

Patterson-Kane, E. G., & Farnworth, M. J. (2006). Noise exposure, music, and animals in the laboratory: a commentary based on Laboratory Animal Refinement and Enrichment Forum (LAREF) discussions. Journal of applied animal welfare science, 9(4), 327-332.

Rajchard, J. (2009). Ultraviolet (UV) light perception by birds: a review.Veterinarni Medicina, 54(8), 351-359.

Silanikove, N. (2000). Effects of heat stress on the welfare of extensively managed domestic ruminants. Livestock production science, 67(1), 1-18.

Smith, M. E., Kane, A. S., & Popper, A. N. (2004). Noise-induced stress response and hearing loss in goldfish (Carassius auratus). Journal of Experimental Biology, 207(3), 427-435.

Wells, D. L., & Irwin, R. M. (2008). Auditory stimulation as enrichment for zoo-housed Asian elephants (Elephas maximus). Animal Welfare.

Surmacki, A., & Nowakowski, J. K. (2007). Soil and preen waxes influence the expression of carotenoid-based plumage coloration. Naturwissenschaften,94(10), 829-835.

Warwick, C., Frye, F. L., & Murphy, J. B. (Eds.). (2001). Health and welfare of captive reptiles. Springer Science & Business Media.

Wells, D. L., Graham, L., & Hepper, P. G. (2002). The influence of auditory stimulation on the behaviour of dogs housed in a rescue shelter. Animal Welfare, 11(4), 385-393.


The Casual Murders: When Do Animal Lives Matter?

*Note: this essay, obviously, discusses animal death. Sensitive viewers are advised to be cautious.

During my college years, I worked for an environmental consulting company for a summer that was mist-netting for bats. If you have never mist-netted for bats (or birds), well, it can be quite a treat. Technicians set up delicate, nearly-invisible nets within gaps in the canopy to catch flying creatures unawares. The purpose of this is to be able to quickly identify and survey what is flying in the area in order to study them; the animals, sparing any accidents, are then released unharmed.

One of the unwilling subjects of our study.

One of the unwilling subjects of our study.

Since we were mist-netting for bats, we had to set up our nets at night, of course, and our nets occasionally caught other flying nocturnal creatures besides bats. We caught flying squirrels on occasion (don’t let their cute looks fool you, they bite far harder than any bat) as well as catbirds and even small owls. But the most frequent unwanted guests in our nets were giant nocturnal moths.

There was the occasional giant, gorgeous luna moth, but more common were brown polyphemus moths and yellow imperial moths. Both of those species are still quite striking and have a wingspan than can surpass the length of my palm, so I have to admit that I was enchanted when I first saw them. And when they got caught in our nets, I wanted to free and release them.


A polyphemous moth.

This was not what most of the biologists and technicians mist-netting for bats did, and a few scoffed at my attempts to rescue the insects. The problem is that it is much harder to detangle a soft-bodied insect from a fine net than it is to detangle a vertebrate with flesh propped up by firm bones. Removing the moths from the nets was time-consuming and inevitably they would come away wounded at best, with many scales missing from their glorious wings due to incessant flapping.

An imperial moth caught in one of our nets.

An imperial moth caught in one of our nets.

My enchantment with the giant moths waned rapidly as I spent more time mist-netting. Their struggles alerted the bats to our nets, driving them away, and on some nights our nets would simply be full of bright flapping wings. And they tended to reward their rescuers by slamming straight into their faces.

I regret to say that I only spent a few nights freeing moths. After a while, I began doing what the more experienced techs and biologists did: I ripped them out in pieces.

It does not sound pleasant, and it was not: I still remember the dreadful popping sounds. And the first time I did it, I was actually sickened by myself, watching the halves of the moth that I had destroyed flap vainly on the ground in the throes of death.


One of my final rescues pictured here.

But that was the first time. As it got later in the season, and we grew busier and busier- netting twenty, thirty, forty bats each night- the removal of moths became methodical.

I bring up this anecdote because it is a good example of animal death becoming casual. Moths are indeed animals, and very attractive ones at that. To have killed so many of them at a point in my life feels very disturbing. I certainly would attempt to free, rather than crush, a moth that I found caught in something now. Why the change? Because I find them less annoying when they aren’t interfering with my work? But isn’t a life a life, no matter the circumstance?

But here’s another wrinkle to this tale. That same summer, I killed hundreds of mosquitoes without a second thought. Both moths and mosquitoes are insects: but only killing the moths feels bad, because they are attractive to my human eyes.

Our perception of death, I think, changes constantly. As I mentioned before, we obviously want to believe that a life is a life no matter what. Yet it is difficult- I would argue impossible- to follow through with this credence. So if all lives aren’t equal, which lives do matter? Most restrict it to animals, ignoring plants, fungi, protists, archaebacteria, and bacteria- even though all those groups combined make up the vast majority of life, of which animals contribute just the tiniest sliver. We believe that animals have more of a right to live even than plants; this is obviously due to our own bias and perceptions.

A series of deer vertebrae I found embedded in the ground.

A series of deer vertebrae I found embedded in the ground.

But fine, let’s limit it to animals. We still give some animals more allowances than others. Moths deserve to live more than mosquitoes because they are more attractive and usually don’t bite us. Vertebrates deserve to live more than invertebrates (with the exception of the charming octopuses and other cephalopods) because they look and act more like us. Furry vertebrates get precedence over reptiles, fish, and amphibians… and so on.

At this point you could bring up the fact that some animals have a greater capacity to suffer than others. A bear, for example, is capable of feeling more complex pain than, say, an earthworm.

A luna moth, battered from an encounter with one of our nets.

A luna moth, battered from an encounter with one of our nets.

This is difficult to flawlessly prove, but probably true. But the thing is that we are not talking about suffering: we are talking about death. There are different shades of suffering; there is only one kind of death, and everybody, from single-celled protist to hairless ape, experiences it the same way.*

So while we can argue a great deal about suffering and the proper contexts that animals and others deserve to live their lives in, death is separate from all that. Death can result from suffering, it’s true. But it’s also true that we often euthanize our pets to stop their suffering.

As Gavroche said in Les Misérables, “Everyone’s equal when they’re dead.” So, again: if a mosquito and a chimpanzee experience death in the same way, is it really right to value one life over the other?

From a biologist’s point of view, yes. It is a factor of numbers: the mosquito population can survive the losses of thousands upon thousands of individuals each summer, but not so the ape population. But in this scenario, based upon populations, the right to life of any individual is totally erased: all that matters is how many there are in total. This would be terrifying if, say, we ever applied it to human populations (and in fact, across history, we have).

A pair of mating imperial moths.

A pair of mating imperial moths.

I’m not in favor of advocating for any lethal human-population control measures myself. Of course I’m not, I’m human too! And I think most humans would agree with this. But the problem is if we then try to apply this same rhetoric to the lives of other animals: simply put, we usually can’t follow through.

I think we all have to admit that we are biased.

And I don’t think that our bias is necessarily a terrible thing.

One of my early rescues rests momentarily on my face.

One of my early rescues rests momentarily on my face.

I don’t know whether valuing the life of an individual mosquito over the life of an individual human is really right or wrong. Right and wrong are quite frequently hard to discern; especially when you realize that there really isn’t a user’s manual on morality. But should we feel ashamed if we value human life over animal life? No, I don’t think so. I think it’s a factor of self-preservation; it’s who we are. And we value the lives of animals that look, act, or think like us more than those that do not because of this sense of self-preservation. Because if we apply death to these individuals, it feels only a step away from applying death to ourselves.

It stems from the most primitive type of morality: empathy. But our empathy is rarely fixed firmly in one place. When I was busy and the moths got more annoying, I killed them; otherwise, I did not. My sense of empathy was totally dependent on the circumstances, and it’s a little terrifying to realize.

When is a death a casual death? When is death excessive, and when is death acceptable?

We all need to admit that the answers to these questions are constantly changing. And I hope you didn’t read through this essay expecting me to give them definite answers: I cannot. If you think you can do it, kudos to you.

Perhaps, though, rather than considering the cost of death to the dying animal, we should focus more on what that death gives to the survivors. A mosquito, as far as we know, will not mourn for one of its smashed brethren: but the loss of a matriarch will shatter an elephant herd. Conversely, the deaths of a few hundred overpopulated deer might alleviate the suffering of their starving, disease-ridden brethren.

Yet this is not still not flawless, because we can’t apply it to humans. We still have to be biased: I think it is wrong to say that a human with no family deserves to live less than a human that would have a hundred mourners at her funeral.

Maybe the final difference there is that we are the only animals who have a concept of death, and are able to stay awake at night afraid of it.**

But who really knows? Again, I don’t claim to have any answers, though I think the most probable one is our inherent need for self-preservation. And honestly: is it wrong?

I am sorry about the moths I killed, though.

A caterpillar, species unknown, dropped from a silken line onto my knee. I set it down in the grass.

A caterpillar, species unknown, dropped onto my knee. I let it crawl away unharmed.



*Ok, not totally. Sometimes it is hard to define death when, say, an individual has their heart transplanted; similarly, organisms can swap cells and pieces of themselves all the time and how do you even define life, for that matter?? Is it just DNA? Are viruses alive?
**It’s interesting that I wrote this article with such a firm concept for what death is, yet now I can’t even come up with a proper definition of it. Well, I’ll see myself out.

White-Tailed Deer Overpopulation in the United States


If you live in the suburbs of the Northeastern US like I do, on any given day you might be able to look out your window and see a herd of deer like the one pictured above. In my neighborhood in particular, I am surprised if a day goes by where I don’t see any.

In 1930 the US white-tailed deer population was down to about 300,000. Today, estimates of how many there are range as high as about 30 million. That’s a 1,000-fold increase in less than 100 years.

What would an ideal number of white-tailed deer be in the US? Scientists estimate the average carrying capacity is about 8 deer per kilometer. The current average? Up to 100 deer per kilometer.

The shift in the white-tailed deer population can be attributed to many factors. In the 1920s the species was actually nearing extinction due to overhunting before government protection programs and national parks sought to save it. You could say that they succeeded. Unfortunately, a number of factors are now leading the deer population to spiral out of control. These include:

  • No predators. Wolves, cougars, and grizzlies, which all once preyed on old, sick, and newborn deer, are now extinct in most states, and much of their former habitat is gone. However, the increase in human population will not stop the deer because…
  • Deforestation actually helps the deer. The white-tailed deer is a species that flourishes in “edge” habitats: that is, habitats along the edges of forests and roadways, as well as newly-planted lawns. This is why they have been so explosively successful in the suburbs. Which also means…
  • Hunting rates are going down. On average, about 6 million deer are killed each year by hunters, though this number is decreasing. By contrast, the deer population will double every other year under ideal conditions; the latest estimate suggests that 12 million fawns were born after the last hunting season. And this number will keep increasing because…
  • Due to the fact that they preferentially graze on disturbed or edge habitats, white-tailed deer populations naturally fluctuate. As such, they have evolved few methods of self-regulation (such as birthing fewer fawns in crowded conditions).

So there are a lot of deer and the population is still growing. The impacts this has are not just the annoying ones that I see every day (deer poop everywhere, deer carcasses all over the roads, destroyed gardens, and the occasional deer attack).

Deer in the US eat 15 million tons of vegetation each year, which costs about $248 million in damage to crops and landscaping in the Northeast alone. About 150 people per year are actually killed due to car collisions with deer. Furthermore, deer carry deer ticks, which can transmit lyme disease to humans.

But the impacts are not limited to us. Native ecosystems are bearing the brunt of the damage. A study on one forest in Pennsylvania found that over half of all plant species diversity had vanished thanks to hungry deer. Other studies suggest that deer prefer eating native to exotic plant species, which facilitates the spread of invasive plants.

This can lead to a cascade of effects on other animal species. Nesting bird populations drop due to the loss of certain tree species (the deer like to eat the new saplings). Insect species, particularly caterpillars, may lose their food sources. Conversely, biting flies and other parasites that prey on deer will increase.

What we should do about the deer overpopulation has been a highly divisive issue in the US; specifically between those who favor lethal vs. nonlethal methods. There is limited success with methods such as fertility control, but these successes are mostly found in closed populations (i.e., fenced in or isolated) and take a long time to take effect.

Lethal methods also have their pros and cons. The possibility of reintroducing wild predators of deer in parts of the US where they are now extinct is often raised and just as often vetoed, given that the bulk of the deer population lies smack dab in the middle of the suburbs.

Similar concerns are raised when people bring up hunting; furthermore, hunters must be advised to take does rather than trophy bucks or they will not significantly affect the population. Studies have shown that controlled hunting programs are effective over small areas, but the effects are mixed over larger ones.

While people argue over what the best way to manage deer is, the population continues to grow and grow, leading to an increase of diseases (such as epizootic hemorrhage disease, which can also spread to livestock) and starvation.

With deer populations going well over carrying capacity in many areas, the risk of population crashes grows. While a crash- which dramatically decreases the number of animals- sounds like it might be a good thing in this case, crashes can be catastrophic. In one famous reindeer crash on St. Matthew island, 95% of individuals died in a single winter.

That, however, is the worst-case scenario, and since few deer populations are so constrained, the more likely one is that deer populations will eventually strike a kind of limbo- not increasing very much but still heavily overpopulated, and constantly on the brink of starvation.

In this case, what is the correct thing to do? The longer we wait, the more damage is done, not just to people, but to the local ecosystem as well. But methods like contraception take several years to really show positive effects, while hunting has to be carefully managed in order to be effective. And this isn’t even bringing in the “moral” aspect of hunting versus nonlethal methods. Yet either way, many, many deer are going to die, and the only way to improve their- and our- quality of life is to dramatically reduce their population.

This isn’t the first time I’ve written about the issues with animal overpopulation- check out my post on rodent plagues. I’ve also written an article about deer with fangs.

To see a list of all animal articles that I’ve written, head to the Nonfiction section of this site.


Alverson, W.S., D.M. Waller, and S.L. Solheim. 1988. Forests too deer: edge effects in northern Wisconsin. Conserv. Biol. 2: 348–458.

Brown, T. L., Decker, D. J., Riley, S. J., Enck, J. W., Lauber, T. B., Curtis, P. D., & Mattfeld, G. F. (2000). The future of hunting as a mechanism to control white-tailed deer populations. Wildlife Society Bulletin, 28(4), 797-807.

Eschtruth, A. K., & Battles, J. J. (2009). Acceleration of exotic plant invasion in a forested ecosystem by a generalist herbivore. Conservation Biology, 23(2), 388-399.

Horsley, S. B., Stout, S. L., & DeCalesta, D. S. (2003). White-tailed deer impact on the vegetation dynamics of a northern hardwood forest. Ecological Applications, 13(1), 98-118.

Insurance Institute for Highway Safety. 2009. Deer-vehicle collisions: no easy solutions but some methods work or show promise. Advisory No. 31.

Iowa State University, 2012. Epizootic hemorrhage disease in deer and cattle.

Kilpatrick, H. J., & Walter, W. D. (1999). A controlled archery deer hunt in a residential community: cost, effectiveness, and deer recovery rates. Wildlife Society Bulletin, 115-123.

Patterson, B. R., & Power, V. A. (2002). Contributions of forage competition, harvest, and climate fluctuation to changes in population growth of northern white-tailed deer. Oecologia, 130(1), 62-71.

Peek, L.J., and J.F. Stahl. 1997. Deer management techniques employed by the Columbus and Franklin County Park District. Ohio. Wildl. Soc. Bull. 25: 440–442.

Piesman, J. (2006). Strategies for reducing the risk of Lyme borreliosis in North America. International Journal of Medical Microbiology, 296, 17-22.

Rooney, T. P., & Waller, D. M. (2003). Direct and indirect effects of white-tailed deer in forest ecosystems. Forest Ecology and Management, 181(1), 165-176.

Rooney, T. P., & Dress, W. J. (1997). Species loss over sixty-six years in the ground-layer vegetation of Heart’s Content, an old-growth forest in Pennsylvania, USA. Natural Areas Journal, 17(4), 297.

Rooney, T. P. (2001). Deer impacts on forest ecosystems: a North American perspective. Forestry, 74(3), 201-208.

Roseberry, J. L., & Woolf, A. (1998). Habitat-population density relationships for white-tailed deer in Illinois. Wildlife Society Bulletin, 252-258.

Rutberg, A. T., & Naugle, R. E. (2008). Population-level effects of immunocontraception in white-tailed deer (Odocoileus virginianus). Wildlife Research, 35(6), 494-501.

Seagle, S. W., & Close, J. D. (1996). Modeling white-tailed deer< i> Odocoileus virginianus population control by contraception. Biological Conservation, 76(1), 87-91.

U.S. Department of the Interior, Fish and Wildlife Service, and U.S. Department of Commerce, U.S. Census Bureau. 2006. National Survey of Fishing, Hunting, and Wildlife-Associated Recreation.

Three Ethical Considerations For Exotic Pets

It’d be tough to give an exhaustive list of which animals I feel it’s morally wrong to keep as pets and which I don’t, because it really is a species-by-species basis. And there are exceptions on both ends- both animals that have very good lives in captivity thanks to capable owners and owners who I would never want to own a cat or dog, much less an exotic pet.

It’s annoying to hear the conversation on exotic pets get sidetracked again and again by the same meaningless statements: on the one hand you have the people saying “that animal belongs in the wild!” which is nice, but adds nothing, and on the other hand you have “cats and dogs used to be wild too!” which just mind-numbingly tosses thousands of years of evolution to one side.

I mentioned before the three* criteria I use when thinking about whether or not I’m morally comfortable with certain species as pets. They are: is the animal captured and sold directly from the wild or does it breed easily in captivity? can the animal be rehomed? and of course, can the animal live a fulfilling and healthy life in captivity?

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