The underGROUND SQUIRREL
Family Sciuridae consists of both tree squirrels and ground squirrels. The prairie dog shape is distinctly squirrel in type with some special characteristics well-suited for navigating underground tunnels: a long quadrupedal body, short legs, plantigrade feet (wherein the entire foot is in contact with the ground during movement), tapered faces with round noses they use to pack dirt with, long claws for digging and moving soil, and eyes high on the head for visibility when peeking out of holes.
Prairie dogs are fossorial mammals. The term fossorial refers to burrowing, specifically species for whom burrowing underground is a necessary part of their lifestyle template. Prairie dogs are burrowing rodents, and their fossorial nature lends the species an air of mystery that has both captivated and frustrated John and other researchers - what is going on underground? Standing in a prairie dog colony, all we can see are the telltale burrow entrances and the dark holes leading to extensive underground tunnels that remain in large part unexplored by research (though advances in technology have pushed us toward strides in this area). For certain species, like the black-tailed prairie dog, these burrow entrance mounds can look like miniature volcanoes protruding from the ground; for others, like the Gunnison's prairie dog, the burrow entrances can be slightly raised and easy to see, or sometimes tiny and so hard to spot you can step right into them even when you're looking for them (field rookies and veterans alike).
Key Invisible Behaviors
The prairie dog burrow is a place of rest and refuge, and certain behaviors, events, and life stages are restricted to the underground, making them invisible to researchers. Over the decades, we have come to define aboveground cues that will tell us what is happening underground. We do not take a single cue but rather multiple cues to make behavioral conclusions. And opportunities to witness typically-underground activities happening aboveground (such as mating) have offered us confirmation that the cues we have refined over the years are accurate.
Though occasional aboveground copulations are observed, the majority of copulations between prairie dogs take place underground. Over the years, John has been able to define and verify several key behaviors indicative of a female going into estrus and copulations occurring. One of the first signs is a male's increased attention in the estrous female, and an uptick in chasing and herding the female into her burrow. These chase herds may occur several times before the male will follow the female belowground. If he remains with her for at least 15 seconds, the interaction is scored as a Both Down (BD). BDs may last anywhere from 15 seconds to several minutes. Several short BDs typically occur over a period of time (sometimes hours) before the critical copulation occurs. The critical copulation can last anywhere from a few minutes to over an hour, and is believed to be the inseminating event.
Using the submergence of the estrous female and her mate as a visible cue, we can track their behaviors to conclude that mating has occurred. Sometimes the male will give us even more indication, sounding a mating call before and/or after the critical copulation occurs. This mating call sounds similar enough to an alarm call that context is needed to differentiate between the two calls. But if we have missed prior BDs, or prior BDs simply have not happened, we can often be cued to a potential mating by following an "alarm call" and seeing that it is, in fact, a mating call. Additional aboveground cues happen after copulation occurs, including the male licking his penis and the female licking her vulva. Often the male or female will also roll in the dirt, which we calla dustbath. Licking and dustbaths do not happen for every mating, and neither do alarm calls, which makes tracking submergences and any missing males (we check for them every 20 minutes) critical during the mating season. You can learn more about mating behaviors under THE MATING SYSTEM.
Parturition is the act of giving birth, and among prairie dogs is strictly an underground activity. On the day a mother gives birth, she will emerge in the morning much later than normal from her burrow (sometimes into the afternoon). There may be no physically distinct sign, though if the researcher is close enough he or she may see blood from the birth. John and the squad make sure to arrive every morning before the prairie dogs wake up and emerge, as most prairie dogs habitually come up around the same time every morning, and knowing typical wake-up times informs us when a pregnant female has remained belowground significantly later than normal.
Prairie dogs spend their first 5-6 weeks of life underground; and with the exception of the mother conducting a transfer from one nursery burrow to another, babies are not seen during their first few weeks. During those weeks, the mother will disappear into her nursery burrow for anywhere from several minutes to an hour or longer to nurse her offspring. We use aboveground cues to confirm that the mother is lactating and her litter is still alive. Before and after birth, the mother will continually bring nesting material into her burrow. Nesting material is typically dry grass gathered in clumps, though as the babies are approaching emergence age the mother may begin to bring fresh grass into the burrow as well (presumably to introduce her offspring to edible greens). Nursing rings during lactation and weaning are most visible after a nursing episode, and the mother's teats will be distended as long as she has offspring to milk. If a mother has lost her offspring, whether to infanticide or unknown reasons, her teats will soon become less visible, and we can use that along with a decrease in other maternal behaviors (defense of the nursery burrow, nesting material collection, and long periods underground) to determine that she is no longer nursing a litter.
Infanticide is the killing of juveniles in their first year. Infanticide may occur underground or aboveground, but the actual killing itself most often occurs within the burrow. Sometimes the killer will emerge from the burrow with the baby; if the baby is not dead, the killing will occur immediately and swiftly; if the baby is already dead, the killer will subsequently cannibalize the carcass. Consumption of the carcass may be partial or full. But for those infanticide events which occur entirely underground, with no carrying-out of the carcass, we must use aboveground cues to verify what has occurred. They include the marauder being submerged (or missing) for 5 minutes to half an hour or longer, followed by licking of the front paws and rubbing the face in the dirt upon emergence, and sometimes even visible blood on the face. Putting all of the context clues together, we can conclude that an infanticide has occurred; final confirmation comes later, as we watch for the victim mother's behavior to turn from maternal to non-maternal, and as we see that no litter emerges from that burrow during the emergence period. Read more about infanticide and cannibalism under INFANTICIDE.
Burrows are also useful for escaping predators. The most significant behaviors for predator-avoidance do occur aboveground (alarm calling, alerting, running away), and submerging underground in the presence of a predator is a last resort. Prairie dogs prefer to stay aboveground so they can see when the threat has cleared. But when the predator gets much too close, sometimes the prairie dog is given no choice and will flee into their burrow. After disappearing for a number of minutes (but sometimes up to an hour or more), a head will bob out and look around. While many grassland predators such as coyotes and birds of prey cannot reach prairie dogs inside their burrows, there are predators that can and will - including badgers, weasels, and snakes. If the prairie dog is fast and lucky enough, they might pop out of an escape route (a connected burrow entrance), but often the predator will reach them in their tunnels before they get that chance. Nocturnal predators like the badger are most dangerous; prairie dogs remain in their burrows throughout the night but some intrepid predators will take advantage of this fact to catch a sleepy prairie dog unawares. Read more about grassland predators under THE PREY ANIMAL.
Sleeping & Refuge
Periods of wakefulness and activity are defined as diurnal (daytime), nocturnal (nighttime), cathemeral (sporadic day or night), and crepuscular (around dawn and dusk). Many species exhibit strict activity periods, and prairie dogs are one of those. As a strictly diurnal species, prairie dogs limit their aboveground activities to daylight hours only. They will submerge into their burrows only for key events or needs, as seen in the list of behaviors on this page. After the sun has set on the prairie, as the sky is growing quickly dark, the prairie dogs will finish for the day and submerge underground for the night. With poor eyesight in the dark, it's important that prairie dogs stay safe in their burrows and avoid encountering possible nighttime dangers; additionally, the burrow offers refuge from overnight weather.
Extreme conditions can quickly put a prairie dog in danger of hypothermia or hyperthermia, and even during the day prairie dogs will use their burrows as refuge from exposure. During cold days, the burrow serves as a hibernaculum of warmth for a few hours; and during hot days, the underground remains much cooler than the outside air. Prairie dogs also take refuge from heavy rain and snowfall, as getting wet compromises the animal's ability to thermoregulate (control its body temperature).