Two weeks have now passed since we first captured the group of male ground squirrels for our phase-shift experiment. These squirrels have been living in an environmental chamber under artificial lights. During this time, the lights were set to turn on one hour earlier than the previous day. This was done for twelve days; by the end of the process, the squirrels were phase-shifted by 12 hours and were now waking up at 9:00 pm. After a few more days with this night time wake up, it was time to release them. At wake-up hour, Team Squirrel moved into action. The idea was to place collars with radio-transmitters and light recorders on each animal. These were not placed on the animals earlier as it was feared they were likely to chew on the antennas while captive. This could still be a problem when they are released, but at least the delay added a couple of weeks to the life of the transmitter. The plan is to return in two more weeks and locate each of the experimental animals with telemetry. It is likely that they will be in the same burrow that they were originally captured from and released to, but there are no guarantees. Male squirrels are known to disperse over distances of a mile or more.
this guy is about to go home
When the squirrels are recaptured, the light collar and body temperature loggers will be recovered and downloaded. We are all placing bets on the length of time it will take the squirrels to resume a normal, diurnal rhythm. The premise of the experiment is that the environmental cues to reset the animals internal clocks are absent or at least not as obvious. The sun is a few degrees higher in the sky at noon than at midnight, and it is usually warmer during daytime than at night. However, local weather affects these a great deal. During the past three weeks at Toolik, we have had more cloudy days than sunny, and the fog seems to clear in the evening. Some of the nights were the warmest and clearest times of the day. On these occasions, that is certainly when the humans left the confines of their labs or cabins to venture outside. Anecdotally, I noticed squirrels might behave similarly. One recent day was cold, windy, and the view obscured by fog from early morning until about 8pm. On a walk we noticed multiple squirrels active until after 11 pm. This is not too surprising based on the weather of the day and their need to get outside to forage for food-especially the females with pups. It also shows that circadian rhythms are not fixed rigidly, but depend also on environmental conditions. Another consideration in terms of cues for the the squirrel's rhythm is the idea that other animals in the immediate vicinity will be active on a regular diurnal schedule, and that the experimental animals will adapt to their rhythm. It should be noted that the Arctic Ground Squirrels are not particularly social, and that after mating season the males have little direct contact with the females and pups. The general consensus among the team was that the phase-shifted squirrels would return to a normal circadian rhythm within 2 to 4 days. I'm leaning to the latter. It is possible that in the absence of significant environmental cues this time could be much longer; only time and the successful recapture of the squirrels, will tell. I'll keep you posted.....
Ear tags are another way of keeping track of individual squirrels
To prepare the squirrels for release upon their 9 pm wake up call, they were individually transferred to our anesthetizing jar for a few minutes of sleepy gas (Isofluorane). Once asleep, the squirrels were weighed (most gained some weight), photograhed (to see fur molt patterns), then the collar was placed around the neck and closed with epoxy. Once the squirrels were all ready, we loaded up for a 20 minute drive to the Atigun study site. I bet the squirrels will be pretty happy to be home. Each one immediately dashed out of the trap and into their burrow.
We plan to recover the light logger and radio transmitter in about two weeks to download data from the experiment.