Life Science

From the field: Unearthing sociality

By Shannon O'Brien

December 4, 2019

I am startled awake by the sound of my phone alarm at three o’clock in the morning. Not a single trace of light can be seen from inside the old Toyota Tacoma. My body aches as I uncurl from the fetal position that I slept in to keep warm in the near freezing temperatures. Once I manage to shut off my phone alarm in my groggy state, there is total silence. Now begins our 68th hour doing round-the-clock radio-telemetry data collection.

My field assistant and I turn on our headlamps before gathering our equipment: a radio receiver, hand-held antenna, and field notebook. Faint beeping from the radio receiver grows louder as we approach our first stop, a low dirt mound in the expansive puna grassland. We carefully point the antenna in all directions to verify we have found the correct spot. A final point of the antenna to the ground and loud chirping from the radio receiver confirms that we have found our target animal. After sticking a marker flag in the dirt to indicate the animal’s location, we walk to the nearest grid flag, counting our steps—perfected with practice so each is one meter—as we go. We read the information written on the grid flag to determine the coordinates of the animal’s location, giving us our first data point of the hour. After gathering our marker flag, we change the frequency on the radio receiver to locate the next animal. A loud chirp from the radio receiver makes me grin. Underneath our feet nest two highland tuco-tucos.

Tuco-tucos are subterranean rodents found in South America, ranging from southern Peru to the southern-most tip of Argentina. While there are over sixty described species to date—making tuco-tucos the most diverse mammalian genus (Ctenomys)—very little is known about their behavior. My keenness to research their behavior brings me 11,500 feet above sea level to Momumento Natural Laguna de los Pozuelos in northwestern Argentina. This remote national park is famous for the 62 square mile laguna that attracts nearly 25,000 overwintering flamingos each year. But unlike the many researchers and tourists that travel to the laguna, I am not here to observe the flamingos.

Historically, most tuco-tuco species were thought to be solitary, with each individual occupying its own underground burrow. However, little scientific evidence backs up that idea. Since the late 1990s, studies using radio-telemetry to track the underground movements and social behavior of tuco-tucos have been conducted for only six of the more than 60 known species. While these studies have shown that a few species are indeed solitary, research conducted by Berkeley Professor Eileen Lacey and colleagues confirmed at least one species is social. The aptly named colonial tuco-tucos (Ctenomys sociabilis) share underground burrows, and females nest together in small family groups. Studies of other tuco-tuco species may reveal that sociality is more common than previously realized.

In a continued effort to gather data on the social structure of multiple tuco-tuco species, Lacey and her team set out to Momumento Natural Laguna de los Pozuelos in 2009 to track highland tuco-tucos (Ctenomys opimus). While some individuals were solitary as predicted, other individuals were unexpectedly found sharing burrow entrances and nesting together. Was this just a fluke? Eight years later, as a graduate student eager to learn more about animal sociality, I journeyed to Pozuelos to retrace their steps.

My team and I arrived on site and set up our trapping grid at the same location used by Lacey, an approximately 1000 by 150-foot plateau. With our grid in place, we hunted for signs of activity. Fresh excavation and feces informed us of likely trapping successes. For the first few days, we set out flags baited with carrots near the entrances of seemingly active burrows. We sat patiently with our binoculars, waiting for tuco-tucos to emerge. Every few hours, we checked our flags to see if any tuco-tucos had nibbled on the carrots.

Confident of the tuco-tucos where-abouts, our team set out live-capture traps baited with carrots at the entrances of active burrows and hid at opposite ends of the field site, making sure all traps were in clear view. After just thirty minutes, a hefty, feisty male thrashed in one of the traps. Before he could escape, we brought his trap back to the truck bed, which serves as our portable laboratory. We efficiently moved through our field protocol by inserting a permanent identification tag under the skin and noting the animal’s weight and reproductive status. A sample from a toe was collected for future DNA analysis to determine if individuals living in social groups are related. Finally, we put a radio collar around his neck and released him back at his point of capture. My team and I repeated this routine over the next few weeks until we were confident that all the adult tuco-tucos in our grid had been captured and radio-collared.

Now, nearly one month after arriving on site, we are collecting radio-telemetry data at all hours to track individual space use and nest locations. What Lacey’s team discovered eight years ago was not a chance occurrence. The ranges of individual tuco-tuco homes overlap extensively, and while some individuals nest alone, others nest in groups of varying sizes. This evidence suggests that the highland tuco-tucos found here are often social and provides the first description of an intermediate form of sociality in a tuco-tuco species.

We collect our final telemetry point for the hour and return to the truck. After set-ting our telemetry gear safely in the back seat, we climb into the front and do our best to make ourselves comfortable. I double-check that my phone alarm is set for 4 a.m. If I’m lucky, I’ll drift off to sleep for the next thirty minutes before my alarm awakens me for the next telemetry round. Just a few more hours until the sun rises, and other members of my field team will come take our place.

Shannon O'Brien is a graduate student in integrative biology

Design: Katya Rakhmatulina

This article is part of the Fall 2019 issue.

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