Deer return to fire-ravaged territories while trees are "still smoldering"

In the recent past, California has seen some of the worst wildfires in history. With more than a century of fire suppression, and the effects of climate change, the wildfires in the area have become bigger and more devastating. Although many species of animals are adapted to surviving the effects of smaller, more frequent wildfires, scientists do not know how animal populations will cope with the consequences of these more severe fires.  

In a rare case of serendipity, researchers from the University of Washington, the University of California, Berkeley, and the University of California, Santa Barbara, were involved in a study at the University of California’s Hopland Research and Extension Center, where the movements of black-tailed deer were being monitored. The team had placed tracking collars on 18 deer and positioned several dozen motion-activated cameras across the area. And then came California’s third-largest wildfire, the 2018 Mendocino Complex Fire. 

The megafire, that burned more than 450,000 acres in northern California, swept through half of the research center’s land and destroyed much of the scientists’ established study site. Instead of giving up on their study, the researchers decided instead to use the wildlife tracking technology and cameras already in place to investigate how deer change their use of space as a consequence of large disturbances like wildfires. They also monitored how this event affected the body condition and survival of the deer. 

“We don’t have much information on what animals do while the flames are burning, or in the immediate days that follow after wildfires,” said co-lead author Kaitlyn Gaynor, a postdoctoral researcher at the National Center for Ecological Analysis and Synthesis at UC Santa Barbara. “It was kind of a happy accident that we were able to see what these animals were doing during the wildfire and right after, when it was still just a desolate landscape.”

“There are very few studies that aim to understand the short-term, immediate responses of animals to wildfires. When a fire sweeps through and dramatically changes the landscape, its impact in those initial days is undervalued and absent in the published literature,” said co-lead author Samantha Kreling, a doctoral student at the UW School of Environmental and Forest Sciences.

The researchers found that all 18 deer survived. Initially, the animals had to flee the flames but they soon returned to their home ranges, despite the fact that some areas of the landscape were completely burned and devoid of vegetation to eat. Most of the deer returned home within hours of the fire, while trees were still smoldering.

“Seeing the drastic changes on the landscape got me wondering what it’s like for animals on the land to actually deal with the repercussions of having an event like this sweep through,” Kreling said. “Having the infrastructure in place was very useful to see what happened before, compared to what happened after.”

Deer returning to home ranges that had been burned had very little to eat. They had to work harder and travel further in order to find green vegetation, and their body condition soon declined. The researchers propose that this strategy of returning to home range, even though the vegetation is burned, is probably a tactic that has helped individuals to survive wildfires in the past. 

However, this loyalty-to-home strategy may prove harmful in the future, as wildfires become more severe. Smaller fires encourage new vegetation growth, which provides good food for deer, but massive wildfires can actually destroy seed banks, which reduces the availability of forage plants. 

“These deer have evolved this behavioral strategy that has clearly worked for them, but the big question mark is, as fires get more intense and frequent, will this behavior actually trap animals in these habitats that are seeing massive disturbances on the scale of nothing that has happened before in their evolutionary history,” said Gaynor.

The authors acknowledge that the response patterns observed for the deer will probably be different from those exhibited by other large mammals responding to unpredictable or extreme events. However, this study does give insight into what extreme disturbances, such as large wildfires, might mean for animals. Kendall Calhoun, co-author of the study and doctoral student at UC Berkeley, will continue to investigate the long-term effects of the fire on the health and reproductive capacity of this population of deer.

The results of the study are published today in the journal Ecology and Evolution.

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By Alison Bosman, Earth.com Staff Writer