WE BEGAN CONDUCTING ULTRASOUNDS on pregnant females last week. Using non-invasive ultrasound technology, we can locate fetusts in utero (in the womb) and conduct counts for every mother. Ultrasounds are critical to answering our research question on offspring survival in Gunnison’s prairie dogs (GPDs). Prairie dog litters can range from 1 to 8 babies at extremes, but more commonly number 4 to 5, born after a 28-day gestation period. Counting fetuses in utero gives us an idea of how many babies to expect when they emerge aboveground 5-6 weeks after birth. Without an underground view into nursery burrows, we can only infer maternal care activities using aboveground cues John has come to define over the years - nesting material collection, mound work, aggressive burrow defense, increased foraging, and tell-tale nursing rings around the female's teats.
Infant mortality before litter emergence can be attributed to many causes, including a failure to adequately care by the mother, a failure to thrive by the infant, and even infanticide (rare among GPDs but accounting for over 35% of infant mortality in black-tailed prairie dogs). In early June, if only two babies emerge from a nursery burrow where we expected three, we can infer that one of the offspring did not make it. Where in the timeline between gestation and litter emergence that baby was lost, we could not say. Perhaps it never made it out of the womb.
It is important that we take care when conducting ultrasounds to get as accurate a count as possible, as it would compromise our data if more babies pop up from the nursery burrow than were counted in utero. Over the last few years, the crew has done a great job with the portable ultrasound machine John uses in the field. Though not easy to conduct, ultrasounds give us a unique and incredible view of prairie dog fetuses in the womb, as bone illuminates white on the screen and backbones can be seen with surprising clarity. Sometimes, even a moving foot appears presses up toward us, and even the most hardened research assistant softens at the sight.