Using Female Antlers to Understand Caribou Landscape Use

Historical Landscape Use of Migratory Caribou: New Insights From Old Antlers

Joshua H. Miller, Brooke E. Crowley, Clément P. Bataille, Eric J. Wald, Abigail Kelly, Madison Gaetano, Volker Bahn, and Patrick Druckenmille

Summarized by Claudia Johnson, who is a geology major at the University of South Florida. She is currently a senior who will be graduating in Fall 2021. She is interested in environmental geology and may like to work in the National Park Service after graduation. In her free time, she enjoys biking and reading.

What data were used? Caribou are a type of deer where both the males and females shed their antlers, contrary to most other deer where only males exhibit this behavior. The female caribou typically shed their antlers after they calve (i.e., give birth). Due to this timing, these antlers can give insight about the seasonal travels of the caribou. These herds have been living on this land for over 700 years but have only recently started being studied. By analyzing past antlers shed, a fuller picture of their history can be put together. This study looked at two herds in the Arctic National Wildlife Refuge of Alaska: the Central Arctic Herd on the Western Coastal Plain, and the Porcupine Caribou Herd on the Central and Eastern Coastal Plains. Their seasonal ranges are shown in Figure 1.

Methods: These antlers were collected from Alaska and analyzed for a number of variables. First, each antler was categorized based on degree of physical weathering by observing how much of the original bone texture was preserved. The antlers were separated into either recent (post-1980) or historical (pre-1980). Next, rubidium–strontium dating, a type of radiometric dating was performed. When a particular isotope of rubidium decays, it slowly decays into stable (i.e., non-decaying) strontium at an extremely consistent rate. So, by measuring the amount of strontium (⁸⁷Sr/⁸⁶Sr) in the bone, they will be able to determine the age of the antler. This analysis was also used to try to determine differences in herds and location by comparing it to available ⁸⁷Sr/⁸⁶Sr in the environment.

Results: A question posed by the researchers was whether the ⁸⁷Sr/⁸⁶Sr of the antlers would be enough to differentiate the two herds from each other in both recent and historical times. This study was able to do so. Comparing the recent and historic female antlers, no difference was found in the ⁸⁷Sr/⁸⁶Sr of the Porcupine Caribou Herd. However, the Central Arctic Herd had many differences, including an increase in variation and ⁸⁷Sr/⁸⁶Sr from historical to recent antlers. These differences in ⁸⁷Sr/⁸⁶Sr are used to understand landscape use, and these findings coincide with existing biomonitoring records, meaning that this is an accurate way to realize historic landscape use. 

Why is this study important? This study was able to provide data on caribou patterns further into history than had been done before in this area. By being able to analyze antlers hundreds of years old, as well as present-day age, the caribou’s response to environmental changes is clear. This study was able to occur because the Arctic provides excellent conditions for the preservation of antlers. The Arctic also provides a valuable setting to study the effects of climate change due to the acute effects of it that occur there. Only the Central Arctic Herd changed landscape use during the interval of change studied here, which researchers concluded was likely due to development for oil exploration, including roads and pipelines that became intrusive to the herd’s ranges in the 1970s.

The big picture: The Central Arctic Herd’s landscape use was shown to be affected by human influence. This solidifies the knowledge that human alteration of land does indeed affect organisms living in the area. In the ranges of this herd specifically, development for oil exploration has been occurring since the 1960s. It was around this time that the pregnant females had to change their old routes to avoid this infrastructure. These principals can be applied to animals elsewhere to better recognize how infrastructural development is affecting the way they live and could be harming them because they must seek out new places to live. 

Citation: Miller, Joshua H., et al. “Historical Landscape Use of Migratory Caribou: New Insights From Old Antlers.” Frontiers in Ecology and Evolution, vol. 8, 22 Jan. 2021, doi:10.3389/fevo.2020.590837.

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