The chicken and the egg – a stable isotope story

Friday is blog day, and this Friday also happens to be World Egg Day! Yes, it seems we even have a special day to celebrate eggs. At Atomic Ecology, we (well, I) take pride in having a stable isotope story for almost any occasion — and today is no eggception (sorry…).

A couple of years ago, as we emerged from the COVID lockdowns and returned to more normal academic routines, I was once again teaching my stable isotope course in person. That meant I could bring undergraduates back into the isotope lab and dream up some fun group projects.

One group of students decided to explore the isotopic signals in their food. Since I happened to have a few backyard chickens at the time, I suggested they focus on eggs. Soon, we were collecting samples from everywhere — from the coop to the Co-Op.

But there was a serious question behind the fun. These students, like many undergrads, were on tight budgets but wanted to make ethical food choices. They were keen to avoid battery-produced eggs but were unsure if “free range” labels really meant what they claimed. So, we designed a small isotope study to test whether those labels actually reflected real differences in hen diets and living conditions.

Our prediction was straightforward:

• Free-range hens, with access to the outdoors, should supplement their grain feed with insects and other critters.

• This would give their eggs higher δ¹⁵N values, compared to battery hens fed mostly on grain.

We compared three groups:

1. “Cheap” eggs from battery chickens,

2. More expensive “free-range” eggs, and

3. A few from my own backyard flock.

After a few lively afternoons in the lab, the results were in — always an exciting (and slightly nerve-wracking) moment for any instructor! Fortunately, this time the data told a clear story.

The eggs fell into three distinct isotopic clusters, matching the students’ predictions beautifully.

Carbon and nitrogen isotope ratios of Battery, home grown and free-range eggs

• Top of the pile: our home-raised eggs — from hens that foraged freely on worms, beetles, and the occasional unsuspecting frog — showed the highest δ¹⁵N values.

• Battery eggs: lower δ¹⁵N values, consistent with grain-heavy diets.

• Free-range eggs: a mixed bunch — some resembled our home eggs, while others showed higher δ¹³C values, likely due to extra corn in their feed.

The students were thrilled: clear data, solid reports, and — most importantly — a tangible demonstration of how stable isotopes can reveal hidden truths about everyday products. The takeaway? In this case, eggs labelled and priced as “free range” really were the real deal.

I often think back to that little classroom project when considering new commercial opportunities for Atomic Ecology. While companies invest heavily in labelling and certification, it’s worth remembering that sometimes the most honest label of all is on the inside.