“Our study helps to emphasize that competitive dominance between the species is more complex than aggression alone.” — Amanda Herbert

“Based on previous research, we expected the duration of aggression to differ based solely on species; however, our results suggested that aggression was dependent on the combined effect of species and flock composition, and not species alone,” lead author Herbert said. “Our study helps to emphasize that competitive dominance between the species is more complex than aggression alone. It also highlights other forms of competition used to outcompete individuals of a different species.”

While competition is alive and well among species of scavengers, it seems Aristotle Onassis may have been right. Alas, the birds of a feather may face more competition from their own species than bullying from their dinner companions of the other species.

“Scientists might need to reconsider their thoughts on how these two species compete for carrion.” — Pat Zollner

“This paper has interesting implications for researchers, primarily that the conventional preconception of black vultures always bullying turkey vultures may not be accurate,” Zollner said. “Scientists might need to reconsider their thoughts on how these two species compete for carrion. More broadly, beyond vultures, studies like Amanda’s that directly compare the influence of exploitative versus interference competition are rare and certainly not common for large birds like raptors. This paper provides a rare and valuable example of a study contrasting these approaches in an understudied system.”

Additional research and next steps

Herbert’s paper is the second from the Zollner lab to be published in 2024, following Marian Wahl’s paper on Taphonomic Signatures of Early Scavenging by Black and Turkey Vultures  in PLOS One summer 2024, which established control measurements from scavenged calves for use in future comparison.

A third article, Drivers of Agricultural Producers’ Tolerance Towards Less-Charismatic Avian Species, exploring the interactions between livestock producers and black vultures in Indiana and Kentucky, co-authored by Brooke McWherter, Zhao Ma from the Human Dimensions Lab and the Zollner lab, was published in the January 2025 issue of Biological Conservation.

Future publications also include Alex Dudley’s research using GPS movement data from 12 black vultures to show how they change their movement patterns in response to deer hunting season. This article will be published in The Wildlife Society Bulletin in 2025.

Wahl will also publish two more chapters of her dissertation based on GPS telemetry data from 24 black vultures gathered during a three-year span. The first will quantify habitat selection by black vultures in ag landscapes in Indiana and Kentucky. The second will look at how black vultures change their movement patterns when their roosts are disrupted as a mitigation measure to ameliorate their effects on people in local communities affected by them.

Landon Jones, a former postdoctoral researcher in the Zollner lab, has been involved in several of the black vulture/turkey vulture projects, assisting with the utilization of the same datasets for multiple projects and publications.

“For Marian’s project on understanding what scavenged calves look like to compare to predated calves by black vultures, we needed cameras on the calves to know when and how vultures were scavenging them,” Jones explains. “Thus, we knew the camera footage would be available later to tease out behavioral interactions between black and turkey vultures. Amanda was then able to go through the camera footage, score the behaviors and write the second paper as a way to double our productivity from that same field effort.

“For my part on the project, all I did was put out some calf carcasses, remove them at the right moments, and help our veterinarian (Grant Burcham) with the necropsies a bit during my first postdoc in the lab. However, while doing that, I enjoyed near constant thinking about how to use that data for extra papers, what ideas to test, hypotheses about how the black and turkey vultures found, consumed and competed over the carcasses, et cetera. Most we couldn’t test or didn’t have data for, but it was still fun and led to some extra efforts or discussion topics that went into one or both papers that we wouldn’t have had otherwise. Some of these ideas connected with a current study I’m finishing on adaptations of bill shape in vultures and carrion-feeding raptors for their respective diets.”

The possibilities for future black and turkey vulture projects from the Zollner lab are endless, but, with help from additional grant proposals and funding, projects could include a deeper dive into the interactions of these two species while scavenging. Specifically, that could include gathering data for longer exposures and at other times of the year.

Editor’s note: Wendy Mayer is a senior communications professional in the College of Forest and Natural Resources at Purdue University.

Angus Beef Bulletin EXTRA, Vol. 17, No. 3-A