Living Clocks of Arctic Animals

The seed of this mornings discussion in neurobiology was “Time, Love, Memory” by Jonathan Wiener. As has been the norm in past weeks we met in the on campus cafe bringing along with us four insightful questions each to keep the discussion rolling along throughout the hour. Wiener describes later in his book (p192) the three necessary components of living clocks. Living clocks are the basis of circadian rhythms and must have an input pathway so that the clock can be reset by the sunrise and sunset. A good example of why this is important is that humans actually have a twenty-five hour clock that resets itself everyday to correlate to the actual day length of twenty-four hours (23 hours, 56 minutes, and 4.1 seconds for any physicists reading this). People who are blind or people who are not exposed to the sun at all will exhibit a twenty-five hour clock, out of synchronization with the earth’s rotation.

So my question was about animals that live near the poles. How do polar bears or lynxes reset their clocks in the arctic summer when the sun doesn’t set? Some thoughts were that perhaps the living clocks are reset by magnetism but quickly realized that there is no shift of magnetism that corresponds to the length of a day. Another thought was that if it’s always light out, does it matter when the polar bear sleeps? The polar bear could have a period of activity, followed by a period of decreasing activity, and then rest and sleep. Lynxes often hunt at night and rest during the day but if it’s always light out does their clock remain synchronized with the earth’s rotation? PZ mentioned there isn’t much research pertaining to this but If anyone knows of any interesting papers that would enlighten this topic post them up.

References: Jonathan Wiener. “Time, Love, Memory.” Vintage Books, A Division of Random House, Inc. New York. 1999.


  1. #1 PoxyHowzes
    November 28, 2007

    Not to go OT here or anything, but earth’s tides change on roughly a 25-hour “day” from lunar influences. Could a “circadian (hu)man” be looney?

  2. #2 Brownian, OM
    November 28, 2007

    If I recall correctly, in The Other Side of Eden Hugh Brody describes the Inuit as staying up and sleeping in later and later as the days in the Arctic get longer, until by mid-summer they’re sleeping during the day and up all night. I don’t recall that he mentions why this is the case, but it is interesting to think that animals (such as humans) living in the high Arctic might vary their sleep cycles so dramatically in different seasons.

  3. #3 Bruce
    November 28, 2007

    I concur with #2.
    Studies have shown that when you deprive human experimental subjects of a sense of time (lock ‘em in a room without a clock, etc.), they settle into a 25-hour cycle, which is also a “lunar day”. I think there have also been some studies that have shown that human women tend to menstruate on a 28-day cycle, but I’ve no first-hand experience with that.
    So I theorize that our bodies are sensitive to lunar cycles, though our minds might not be, and when our minds have nothing to synchronize on, our bodies latch onto tides. Maybe it qualifies as ESP, but not as crackpot-ish.
    Only way to test my theory is to remove humans from earth; guess I should apply for a research grant while Bush is anxious to get to the moon. Could be a good research subject for the space station occupants.
    What about the humans posted to the south pole for extended periods?

  4. #4 faunistic
    November 28, 2007

    When visiting my son and his family in the Yukon this past summer, I wondered what do strictly nocturnal (as opposed to crepuscular) mammals such as northern flying squirrels do under the midnight sun. What about bats?

  5. #5 ACW
    November 28, 2007

    The mean solar day is as near as makes no difference to 24h 00m 00s. In fact, the original definition of an hour was “one twenty-fourth of a mean solar day”. The current mean solar day is about two milliseconds longer than exactly 24 hours. A mean solar day is the average elapsed time between consecutive local noons, averaged over a long timebase.

    The poster mentions a different period in a parenthesis: 23h 56m 4.1s. This is the length of a sidereal day, which is the average elapsed time between meridional transits of an arbitrarily-chosen distant star. Our biological clocks resynchronise, not to the stars, but to the sun, and so the length of the sidereal day is not relevant.

  6. #6 Coturnix
    November 28, 2007

    Also, there was a study on small mammals in the Arctic recently.

  7. #7 g
    November 28, 2007

    What’s the variation of that “25-hour cycle” among individual humans? Is it closer to 25 +/- 0.5 hours, or 25 +/- 6 hours?

  8. #8 Bruce
    November 29, 2007

    But more relevant to the arctic animals, tidal amplitude has much to do with the declination of the moon, which varies about 27 degrees north and south, and the sun declination. Resonances in local bathymetry affect tide height, a bit different from amplitude. So with Sun and moon at same 20 degree declination on a hypothetical smooth and spherical Earth, tidal effects at 80 degrees latitude match those at 40 degrees in the other hemisphere.

    So if migratory birds can sense Earth’s magnetic field, maybe arctic lynxes can sense the tidal variation.
    Should be someone out there smart enough to devise an experiment.

  9. #9 Eddy
    November 29, 2007

    IIRC, a day is, always was and will always be 24 hours. The time it takes the Earth to rotate the full 360 degrees around it’s axis, on the other hand, is about 23 hours and 56 minutes. explains the difference.