It’s a warm, humid evening. The sun is low. Birds begin their evening songs. And in the soccer field, there is an odd sight. Among the children, most of whom are not paying attention, the coach is limping around the kids. She’s a little bit hunched over, sometimes rubbing her legs and complaining about “horrible aching and sore muscles for no apparent reason.”

As practice comes to an end, the kids run off to their parents. And finally, the 21-year old volunteer kids soccer coach, Coach Jen, eases into the bleachers for some temporary relief and spends time catching up on text messages and emails, all while enjoying a sleeve of cookies.

Her face is the picture of both guilt and delight as she explains that her husband bought her eighteen boxes as a gift, and she’s been enjoying them for breakfast lunch and dinner.

The following Wednesday, Coach Jen had to call off practice. The pain was too much. But there was a game that Saturday. To keep the kids at least somewhat in shape, she emailed the parents asking them to try to run certain drills and make sure they get some good protein and healthy food.

That’s when it hit her.

For the past week and a half, Coach Jen’s diet had been mostly cookies. It was only when considering the nutrition of the kids on the team that she realized her own nutrition might be suffering. This was a lesson to her as a new adult without the frequent guidance from her mom. She could eat whatever she wanted, whenever she wanted. But that might be what was leading to the pain she was having.

Upon skimming over the box’s nutrition facts, Coach Jen was even more convinced this was the problem as the cookies were lacking a lot of important vitamins and minerals.

Lacking nutrition, sometimes one single micronutrient can have disastrous effects. This is as true for humans as it is for animals.

A significant example was seen in the European hamster, where a lack of a certain micronutrient resulted in filial cannibalism. That’s the nice way of saying the mother hamsters were eating their pups.

European hamsters can be found in grasslands and farmlands in parts of Europe and Asia. But recently, they have been in such extreme decline that they’re considered critically endangered (Tissier et al., 2017).

In 2017, Mathilde Tissier set out to evaluate how diet within monoculture farms affected hamster reproduction.

Monoculture farms are farms cultivating only one single crop or organism at a time. While monoculture allows scaled farming and widespread food production for people, it creates an ecosystem of very little nutritive diversity. And this can impact all wildlife present within that ecosystem.

This was believed to be the case for the European hamster residing in these crop fields. They fed mostly on the wheat or corn grown in the fields along with any worms found in the area.

Tissier looked at four food combinations: wheat with clover, wheat with worms, corn with clover, and corn with worms. Because corn (maize) was higher in energy than wheat, she predicted an observation of better reproductive outcomes for corn-fed hamsters.

Additionally, Tissier set up a secondary experiment looking at the effects of B3 supplementation. This was because a previous study showed corn was deficient in B3 leading to impaired growth in rats.

The surprising result was that the hamsters fed the wheat-worm combination had an 80% pup survival rate. In both of the corn-fed groups (corn with clover and corn with worms), pup survival rate was drastically reduced.

While all groups did not have a problem giving birth, the low survival rate in the corn-fed group was due to litter suppression, that is, the mothers ate their pups (95% of the cases).

What happened when the corn-fed hamsters were supplemented with B3? Their number of weaned pups increased by 85% (Tissier et al., 2017).

It’s easy to neglect the nutritional cost of reproduction. But essentially, one body is using its resources to produce another.

Components of bird eggs, for example, include protein, albumin, water and of course calcium carbonate (Leonard, 2017).

While calcium is a pretty ubiquitous mineral, what can happen in the birding community and reptile community is an overfeeding of one food type, particularly meal worm.

Meal worm has a low calcium content, which can be more problematic during egg-laying (Zwart & Rulkens, 1979).

Carolina chickadee with a meal worm.

In a study on the great tit bird species, researchers found that calcium deficiencies led to more fragile eggs, egg eating, and disruption in egg laying. Furthermore, a lack of calcium led to birds searching even more for calcium sources, even consuming sand and dirt when levels were low (Graveland & Berends, 1997).

Great tit bird eggs (Parus major) in a nest of moss and lined with fur. This photo shows 11 eggs. Typically, a bird will lay one egg a day, usually in the morning. Though this photo makes the eggs look large, they are only about the size of jelly beans.

Great tit birds (Parus major) are found throughout Europe and parts of Asia.

During egg-laying, observed females consumed 1.7 times the amount of calcium needed for the eggshells (Graveland & Berends, 1997).

This is one reason why some bird enthusiasts will supplement meal worm feeders for their backyard birds with pulverized eggshell (from hens).

But birders delight in another bird and put out a very distinct feeder for them: hummingbirds. The traditional composition of food people put out for hummingbirds is four parts water to one part sugar.

This diet alone, especially for the rapid hummingbird metabolism, could be fatal for their system. It wouldn’t take much to create a biochemical imbalance.

Fortunately, hummingbirds are not solely reliant on hummingbird feeders. In reality, these feeders just allow us to watch these tiny birds up close. Hummingbirds also fulfill their protein and mineral needs with insects.

Ruby throated humming birds at a window feeder.

Just like with other birds, however, the calcium demand during egg-laying can lead hummingbirds to take interesting approaches to supplementing calcium.

When studying Rufous Hummingbirds, Michael Adam and James des Lauriers discovered females eating soil. They hypothesized the hummingbirds did this to supplement mineral deficiencies, especially calcium deficiencies.

Adam and des Lauriers believed this was especially true given the cooler climate, which can influence electrolyte balance, and the low insect population of the area (1998).

In their limited study, they took soil samples from the areas of observations and analyzed it for minerals such as potassium, phosphorus, magnesium and calcium. Of the minerals, the soil samples were rich in calcium.

Further supporting their belief that this behavior was attributed to hummingbirds needing to supplement their calcium intake was that the observed behavior mostly occurred for females during breeding season. Many other studies have been published reporting birds eating sand, dirt, bone, snail shells and other calcium-rich items, and most of the observed behavior occurred in females (Adam & des Lauriers, 1998).

The need to balance calcium is, of course, not restricted to birds. Mammals stripping bark or gnawing on bone and antlers is believed to be attributed to a need to supplement calcium as well as other minerals, and has been especially observed in female and young mammals (Nichols et al., 2016).

Calcium is not the only micronutrient that needs supplemented. As illustrated by the European hamsters, animals can become deficient in any other type of micronutrient, especially when there is little variety in their diet or they have an underlying illness. This can ultimately lead to sickness, physiological issues and unnatural behavior.

So what did Coach Jen do after she discovered the possible reason behind all her body aches was poor nutrition?

She made it a point to vary her diet by eating healthy proteins, green vegetables and taking a multivitamin.

By game day, her aches were manageable. And by the following week, she had zero complaints and a valuable lesson.

The soccer game ended in a tie, by the way.


Adam, M. D., & des Lauriers, J. R. (1998). Observations of Hummingbirds Ingesting Mineral-Rich Compounds (Observaciones sobre Zumbadores Ingiriendo Compuestos Altos en Minerales). Journal of Field Ornithology, 257-261.

Graveland, J., & Berends, A. E. (1997). Timing of the calcium intake and effect of calcium deficiency on behaviour and egg laying in captive great tits, Parus major. Physiological Zoology, 70(1), 74-84.

Leonard, P. (2020, May 28). The Beauty and Biology of Egg Color. All About Birds.

Nichols, Christopher P., Julian A. Drewe, Robin Gill, Nigel Goode, and Neville Gregory. "A novel causal mechanism for grey squirrel bark stripping: The Calcium Hypothesis." Forest Ecology and Management 367 (2016): 12-20.

Tissier, M. L., Handrich, Y., Dallongeville, O., Robin, J. P., & Habold, C. (2017). Diets derived from maize monoculture cause maternal infanticides in the endangered European hamster due to a vitamin B3 deficiency. Proceedings of the Royal Society B: Biological Sciences, 284(1847), 20162168.

Zwart, P., & Rulkens, R. J. (1979). Improving the calcium content of mealworms. International Zoo Yearbook, 19(1), 254-255.

Coach Jen story is based tightly on a true event but with changed names for anonymity.