Many years ago, I visited a friend of mine, John, who had taken up an internship at the United Nations in New York and had kindly offered to host anyone who wanted to experience this part of the USA. As a wide-eyed 20-something, I had a brilliant time exploring the city and all its vibrant cultures. Unfortunately, just before I returned home, John and I came down with a very nasty case of food poisoning. We suspected pizza from Grand Central Station, but let’s not point fingers.
One of John’s housemates was a chef, and she brought us a huge brown paper bag full of bread and soup and other wholesome ingredients to make us feel better. Right at the bottom of this paper bag were two large, ripe, plump oranges. Instinctively, both John and I reached for them. It was as if something was telling us, “These are what you need to feel better.” This memory has always remained with me.
Did my body instinctively know what I was lacking? What I had lost due to the illness and what I needed to make it better? Are we, as humans, good at acting on an inherent “nutritional wisdom”?
Balanced diets and nutritional wisdom
It goes without saying that providing a species with the correct diet – one that provides for all a species’ nutritional needs, promotes its physical health and enables the performance of natural feeding and foraging behaviours – is essential to keeping a species alive. Therefore, good nutrition is one of the most fundamental needs for captive husbandry and care.
Good nutrition is one of the most fundamental needs for captive husbandry and care
Even though we might provide the animals under our care with “a balanced diet”, species may not consume food in the way we hope or plan for. Individual animals may be selective in the dietary ingredients they choose to eat, consuming more of some food items than others and therefore not actually eating their total balanced ration.
If we consider the three examples in Figure 1, will the parrot, tortoises and geese have an inherent understanding of what they need to consume at a particular time on a particular day to ensure they always meet their energy, physiological and nutritional demands?
A balanced diet?
But first, let’s consider what we mean by a “balanced diet”. Feeding a “balanced diet” means providing a combination of nutrients in the appropriate proportions to meet a species’ specific nutritional requirements for maintenance, growth and development, reproduction and overall health. A balanced diet ensures that the animal receives adequate amounts of essential nutrients – proteins, carbohydrates, fats, vitamins and minerals – and energy in the right ratios for optimal physiological functioning.
Water is also a critical component of a balanced diet as it is essential for digestion, nutrient absorption, temperature regulation and waste elimination. Some species get their water entirely from their diet, whereas others need to drink to ensure they maintain adequate hydration. Thus different water consumption strategies must be factored into nutritional husbandry.
Some species get their water entirely from their diet, whereas others need to drink to ensure they maintain adequate hydration
Specific nutritional requirements vary by taxa, life stage (eg growing animals, lactating females and animals in moult) and health conditions. Feeding practices should consider these factors to tailor the diet to the unique needs of the animal. An animal’s physiological state, the availability of nutrients in the diet and the bioavailability of those nutrients for proper absorption and usage will ultimately impact how good a diet is at meeting an individual’s needs at a particular time or life stage.
For example, zebras are found across the plains of East Africa. Although zebras may look similar, the different species have differing ecologies and have evolved different traits to enable survival within a specific environment (Rubenstein, 2010).
The plains zebra (Equus quagga), the familiar species from Serengeti-featuring wildlife documentaries, lives in stable social groups in grassland habitats that provide more constant supplies of grazing and fresh water. This type of habitat is described as “mesic”, and the regularity of available resources means plains zebra herds are more harmonious and less competitive. Plains zebras also have the relative luxury of accessing water daily.
On the other hand, the larger Grevy’s zebra (Equus grevyi) occurs in xeric habitats, where food and water are widely separated and food resources can be patchy in distribution. Animals in these habitats need to travel long distances to access these resources, making herd animals more transient because of increased competition. Grevy’s zebras are larger than the plains zebra – in fact, this species is the largest of all wild equids – and this large size means it can drink less regularly to cope with environmental challenges.
Both species of zebra avoid competition when overlapping in the same range because they do not select for the same types of plant material (Rubenstein et al., 2016). Their differences in need for water dictate what sorts of vegetation they consume (Figure 2). Just because your equid is African, black and white and stripy does not mean it is the same as any other stripy black and white equid when it comes to husbandry and care.
What is nutritional wisdom?
The concept of “nutritional wisdom” refers to an organism’s ability to make appropriate dietary choices based on its nutritional needs (Provenza, 2018a). While the human animal can exhibit nutritional wisdom by selecting foods that provide essential nutrients, the same cannot be said for all non-human animals all the time (Harrison and Mcdonald, 2006). In fact, recent research has demonstrated that humans are actually much better at using their inherent, in-built nutritional wisdom than was previously thought (Brunstrom and Schatzker, 2022).
The concept of ‘nutritional wisdom’ refers to an organism’s ability to make appropriate dietary choices based on its nutritional needs
Wild animals are free-roaming and able to determine what they eat and when. They will choose from a variety of different dietary items that, overall, provide a diet of the correct nutritional quality and energetic density (Provenza, 2018b). However, there is debate as to whether domesticated animals can show this same degree of nutritional selectivity and flexibility when it comes to their choice of food. Has the process of domestication reduced their instinctive abilities to choose what is right for them? Debates and discussions continue.
The many species of wild animals have ultimately evolved to survive and reproduce, and their behaviours relating to feeding and foraging support these wider important goals. Free-living animals typically face unpredictable and variable food sources. In different habitats and different parts of its range, a species can show distinct seasonality in how it collects food and what it will choose to eat based on food availability, competition and other extraneous pressures.
Why don’t some animals show nutritional wisdom?
Several factors contribute to the absence of nutritional wisdom in animals, and these can be explained through evolutionary, physiological and behavioural perspectives, as well as by the challenges (and limitations) they face in the environment they are currently in. This latter point is particularly relevant to individuals managed under human care.
Several factors contribute to the absence of nutritional wisdom in animals, and these can be explained through evolutionary, physiological and behavioural perspectives
Physiological mechanisms
Animals often lack the physiological mechanisms necessary to assess the nutritional content of their food accurately. Humans, with their developed taste buds and a more sophisticated sense of taste and smell, can discern various flavours associated with specific nutrients. In contrast, many animals rely on basic taste and olfactory cues, which may not provide detailed information about the nutritional composition of the food.
Animals are adapted to specific ecological niches and local environments, where food sources may vary in nutrient contents. Evolution has shaped their digestive systems and metabolic processes to extract nutrients efficiently from the available food sources rather than to select foods based on nutritional composition.
At certain times of the year, animals may have to prioritise maximal energy intake over specific nutrient intake. In the wild, obtaining sufficient energy for survival and reproduction is crucial, and animals will adopt strategies such as opportunistic feeding to meet their energy needs without necessarily considering the balance of specific nutrients. When resource availability improves, feeding habits change back to enable the consumption of a more “balanced diet”.
Selective feeding behaviours
Species display selective feeding behaviours based on specific needs, which can be responses to immediate cues rather than demonstrating a comprehensive understanding of nutritional requirements. One example is the use of clay or salt licks by elephants or parrots in response to ingestion of under-ripe fruits, nuts or vegetable matter that contains high levels of anti-nutrients, such as tannins.
Conversely, these behaviours can be taught to others and passed on across generations, as in the case of elephants visiting the same patches of mineral-rich soils in the rainforest (Hii, 2017) because it is essential to how the animals digest their food. Such dietary information may be passed down between individuals in a group (Cassini, 1994). In fact, nutritional wisdom is often a by-product of social learning – learning new behaviours by observing and emulating the behaviours of others around you. The social environment provides young or inexperienced individuals with opportunities to see what food is edible and to learn how to collect and process it.
Dietary information may be passed down between individuals in a group. In fact, nutritional wisdom is often a by-product of social learning
In captivity, many species in the parrot family suffer from nutritionally related pathologies and behavioural problems caused by poor or inappropriate husbandry (Brightsmith, 2012). In the wild, parrots are naturally social and consume a mixed diet made of different seeds and nuts (among other things). Due to the complexities of avian digestion and the assimilation of nutrients, it can be difficult for birds that consume mixed diets to know what is best for them (Clarke, 2010). But evidence shows that inexperienced individuals learn from group members about what is best to eat – the social unit helps birds forage efficiently and appropriately by teaching them the best types of foods for a specific time of year.
How can we understand nutritional wisdom in non-human species?
Understanding nutritional wisdom in non-human animals is complicated. Owners should look at the information that is currently available on what a species will eat, and present diets according to reliable information and advice from experts.
Veterinary professionals should remain up to date on the evolving world of nutritional research for species they commonly see and be able to advise owners accordingly. Being able to identify any clinical signs of a nutritionally based disorder and recommend changes to feeding practices and husbandry accordingly will also be of great help to long-term improvements to animal health and welfare, for example recognising abnormal feather colouration (red instead of yellow) in a blue-and-gold macaw (Ara ararauna) (Figure 3).
This change in pigmentation is likely a cause of malnutrition, which is often associated with a bird being a “picky eater” and only consuming a diet high in sunflower seeds and pigments. The lack of nutritional wisdom on the part of the bird and a lack of understanding of macaw nutrition on the part of the owner can cause hepatic lipidosis and more chronic health issues (Harrison and Mcdonald, 2006; Salavati et al., 2023). It is important to remember that the quality of a bird’s feathers is an important clue as to its nutritional status.
Final thoughts
Going back to my story about being sick in New York and the magnetic draw of the orange, it seems I was experiencing the same cravings for good, honest fruit and vegetables that occur when humans are subject to a specific nutritional deficiency. Knowledge of the benefits of vitamin C from fresh fruit in combating scurvy is centuries old. Sailors would describe a craving for fruit as one of their first symptoms of the disease, a craving that would intensify as the deficiency worsened (Lamb, 2011).
Maybe animals are also capable of experiencing these kinds of urges? Perhaps we have only just scratched the surface with our knowledge of how species feed and what they feed on
Maybe animals are also capable of experiencing these kinds of urges? Perhaps we have only just scratched the surface with our knowledge of how species feed and what they feed on, including the potential variety of dietary ingredients some animals will choose to select. What is clear from this review is that animals in a free-living state will maintain a correct plane of nutrition to meet energy and physiological demands when provided with the resources and the choice of access to these resources. Our job is to mirror this key part of a species’ ecology in our captive care regimes.
