Reconstructing Miocene bird mating behavior from a fossil track site

By: Nasrollah Abbassi 

Summarized by: Elizabeth Kolosovskiy is a senior at Binghamton University, majoring in biology and minoring in forensic health. She plans to graduate in December and take a few months off to travel before coming back in May to start the accelerated nursing program at Binghamton University to obtain her second degree. During this time, she plans to continue working at UHS Wilson Memorial Hospital. After earning her degrees, she plans to continue to advance her education to become a CRNA. When she is not working or studying, she enjoys going to the gym and spending time with her family and friends.

Data: Scientists studied a small, fine-grained sandstone slab predicted to be between 7.5 – 17.5 million years old that they found in the Chehr-Abad area, 90 kilometers west of Zanjan, Iran. More specifically, they found the slab 1,256 meters above sea level on the side of a cliff within the Upper Red Formation (URF). The URF is a universally important Miocene rock unit in Northwest Iran, known for its distinctive red color, which is attributed to the presence of iron in the rock. This formation enabled scientists to learn that the Miocene was a warm and dry period characterized by many diverse species that lived in deserts or plains with occasional sources of water, such as rivers, providing a better understanding of how ecosystems changed over time and why. The slab researchers removed contained 70 small tetradactyl (a bird with four fingers on one limb, three facing forward and one backward) footprints left in various patterns based on the different movements that were most likely made during mating dances.

Hypothesis: Behavioral traces do not always fossilize, and if they do, it is difficult to predict what organism created them because the organism that made the trace does not usually fossilize alongside it and can leave more than one type of trace behind. However, these fossilized bird mating prints were distinct and well-preserved. Since modern birds exhibit specific mating behaviors that also leave behind traces, scientists hypothesized that they can gain a deeper understanding of contemporary bird behaviors by drawing parallels between these ancient traces and modern traces.

Methods: Scientists were not able to collect the full sample due to the difficult terrain, so researchers took detailed photos of the remaining slab using a quadcopter (drone with four spinning propellers and a camera). They then combined all the images to measure and shape the footprints and tracks using Adobe and Photoshop software. Researchers identified features of the footprints, such as length, width, angle, pace, stride, and area, to help differentiate between various behaviors. They measured the distance between the left and the right tracks to determine the pace, the distance between a set of two left or two right tracks to determine the stride and measured how far each track was pointing from the line of travel (a straight line down the center of the tracks) to determine the angle of the track. After grouping each track into a behavior type, scientists recorded how often one behavior led to another, excluding a track if it only showed one behavior (Fig. 1). Finally, they used a a statistical test called a Markov chain that assumes that each behavior occurs based on the one that comes before it and compiled these results into a chart that shows how many times a behavior changed and the probability of the change occurring. This helps scientists understand if there is a pattern in the tracks. 

Results: Scientists discovered seven types of behaviors in the fossil tracks: walking, high stepping, stomping in place, short-distance flying, hopping, pecking, and lateral leaping. Walking was the most abundant movement, characterized by a straight line of tracks with a consistent, repeated pattern in stride and pace. High-stepping was the second most common behavior, marked by many newer footprints overlapping the ends of older prints in a dense, repeated pattern, all in one spot. Stomping was the third most abundant movement, characterized by multiple small areas at the beginning, middle, or end of tracks with overlapping, dense footprints similar to high-stepping, but accompanied by digging. Short-distance flying was indicated by short gaps in tracks with no footprints. Finally, hopping was identified by paired footprints, pecking was shown by repeated scratches on the side, beginning, or end of tracks, and lateral leaping was the least abundant behavior, characterized by short lateral jumps and are found within high-stepping tracks (Fig. 5). When analyzing the data they obtained on the transition of behaviors they ruled that there was a relationship between hopping and singing, but that they needed more data from other ancient and modern dances to compare and definitively determine a pattern. However, when comparing the tracks’ shape and patterns to those of modern birds, they were able to definitively state that these footprints represent the same quick movements used by modern avian birds during complex mating tap dances and that multiple animal organs were involved. Since the measured prints were 20 mm long and wide, scientists estimated the birds to be around 6cm tall and believe the tracks and peck marks belong to a species closely related to modern semi-aquatic plover birds, called Gruipeda fuenzalidae.

Significance: This trackway fossil is significant because it is some of the only fossil trace evidence has been found showing bird dances from millions of years ago. This helps scientists understand and track how bird behavior evolved, rather than focusing on the birds’ change in morphology and assuming bird behavior from this. This discovery also led to the creation of a new behavioral fossil classification category, called Goshnichnia, for fossil mating traces.

Broader Implications beyond this study: The discovery of this fossil track and the creation of a new behavioral classification category mean researchers will be able to assess more data for comparison between species and time periods, confidently determine more mating tracks and patterns, and predict how these changes influenced survival, reproduction, competition, and whether there was environmental influence.

Citation: Abbassi N. (2025). Reconstructing Miocene bird mating behavior from a fossil tracksite. Scientific reports, 15(1), 25563. https://doi.org/10.1038/s41598-025-11727-y