Discovering Secrets of the Andean Condor through an Ancient Fecal Time Capsule Dating back 2,200 Years

The Andean condors have been nesting and pooping in the same cliffside grotto for over 2,000 years. This massive pile of guano is granting scientists a never-before-seen glimpse into the birds' past as well as revealing their surprising adherence to raising chicks in the same location even when the region was going through significant changes.

The study of the deposit indicates that the condors transformed their diet after the European colonization in the Americas. Researchers report in Proceedings of the Royal Society B that the birds had, in fact, abandoned the site for a millennium, likely because of continuous volcanic eruptions.

"This material was once considered useless and overlooked, but it can actually provide a wealth of information on how populations, communities, and ecosystems adapt to environmental changes," says Rachel Reid, a paleoecologist at Virginia Tech in Blacksburg who was not involved in the research.

The Andean condors, which are the largest birds of prey with a wingspan of over three meters and a weight like that of a toddler, are only found in the Andes Mountains in South America and along the western coast of the continent. These birds are threatened with extinction, with only around 10,000 remaining, and their numbers are decreasing, making the need to understand their behavior and ecology increasingly critical.

However, studying Andean condors is challenging because they mostly spend their time on the wing in remote mountain areas. According to paleoecologist Matthew Duda of Queen's University in Kingston, Canada, the birds are difficult to capture and monitor.

In 2014, Duda's colleagues discovered a condor nest in Argentina's Nahuel Huapi National Park that was in a cliffside nook, which turned out to be a treasure trove of information. Researchers had to rappel down ten meters along the cliff and then hike an hour from the nearest road to reach the nest. Unlike most condor nest sites, this nest was secure from snow and rain, and thus, the droppings of successive breeding pairs accumulated layer upon layer, forming a dense, pale mound.

The poo's well-preserved information presented the ideal opportunity for the researchers to transport themselves back in time, according to Duda. They then carved a 25-centimeter-deep slice from the guano pile, and by examining DNA and ratios of certain chemicals in the excrement, they were able to determine what the condors had eaten over time. Other chemicals, including sulfur and potassium, as well as algae that was well-preserved, allowed the researchers to discover the changing environmental conditions.

According to the chemical dating of the samples, the deposit's oldest layers were at least 2,200 years old. Duda states that it is "extremely surprising" that the condors had been utilizing this nest site for so long. While most bird species return to the same area to raise young, they rarely use the same nest repeatedly. "If they keep returning to the exact nest over and over again, it implies that where these birds are nesting is integral to their ecology and behavior," he adds.

The researchers noted that the rate at which feces accumulated slowed down substantially from 1,650 to 650 years ago, decreasing from 0.08 cm per year to 0.003 cm per year. According to the researchers, this slowdown implies that the condors had abandoned the site for a millennium. During this time, nearby volcanoes underwent a series of eruptions. Thick ash covered the vegetation in the surrounding region, prompting herbivores to move away, resulting in fewer carcasses for the condors to consume, believe Duda and his colleagues. The birds must have flown away to hunt in other greener pastures and returned to the area after the volcanic eruptions stopped.

Dulcinea Groff, a paleoecologist at the University of Wyoming in Laramie who was not involved in the research, says that guano records have previously shown how eruptions lead to a decline in bird populations.

Duda and the researchers have also discovered a substantial shift in the condors' diet. Prior to European colonization, the birds primarily ate beached whales and some native mammals like llamas and guanacos. However, in recent centuries, their diet has mostly comprised of livestock like sheep, cows, and goats.

Their findings indicate that those condors that lived several centuries ago did not have high lead and mercury levels in their bodies, unlike modern condors. These toxic metals collect in scavengers that eat carcasses shot with lead ammunition. Scavengers excrete some of the metals in their droppings, which scientists can detect. The study helps confirm that heavy metal pollution is a recent issue.

The research “gives us a much longer timeline to understand what the natural variability is in a population,” Duda says. Since this study is a snapshot of just one nest, he and colleagues plan on collaborating with other researchers to find similar condor nests to see whether the same patterns written in guano emerge.

In the meantime, the condors’ apparent loyalty to this very specific nest site — even potentially through centuries of volcanic mayhem — highlights just how crucial the preservation of such sites may be for their successful conservation, Duda says.