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In this week’s eSkeptic, William D. Stansfield asks whether groundhogs and swallows are really able to predict the arrival of spring as accurately as reported in the popular press. Stansfield is Emeritus Professor in the Biological Sciences Department at the California Polytechnic State University.


Punxsutawney Phil from the official website of the Punxsutawney Groundhog Club

Punxsutawney Phil and
Animal Weather Predictions

by William D. Stansfield

THERE IS A GROUNDHOG NAMED PUNXSUTAWNEY PHIL living on Gobbler’s Knob, located about two miles east of the town of Punxsutawney, Pennsylvania. On February 2 each year, Phil is said to wake from hibernation and amble outside his den. According to tradition, if he sees his shadow and returns to his den, the country will have six more weeks of winter weather. But if Phil does not see his shadow, spring will be “early” that year. According to the Punxsutawney Groundhog Club, Phil is immortal and has been making these weather prognostications for the last 123 years. Phil and the town of Punxsutawney were immortalized in the 1993 movie Groundhog Day, starring Bill Murray, although the scenes were really filmed in Woodstock, Illinois.

Groundhogs (Marmota monax) are also known as woodchucks. They are common rodents of northern and eastern North America. They eat mainly grasses during the warmer half of the year and build up large amounts of body fat in preparation for up to six months of hibernation sleep during the colder months. Ground squirrels, jumping mice, marmots, and woodchucks are true hibernators whose body temperature drops to almost that of the ambient temperature of their underground burrow or den. Breathing may slow to as few as one breath every five minutes. Groundhogs will awaken if the den temperature drops dangerously low and shiver or move around to raise its body temperature through muscular activity. Other mammals that experience prolonged periods of torpor without true hibernation, such as bears, badgers, opossums, and racoons, reduce their breathing rate significantly, but their body temperature remains almost normal. Hibernating bears can be awakened if sufficiently disturbed. A biologist found this out the hard way when he tried to take a sleeping bear’s rectal temperature with a thermometer.

Actually, Phil is cared for by members of the club year round. Viewing the video of this year’s celebration of Groundhog Day on the club’s website, we see that Phil’s den is a poor imitation of a dead tree stump with a hinged door that is opened by his handler and Phil is pulled forth on February 2 to meet the people who have come to witness the ritual. The time of day is not specified. However, one photograph on the club’s website shows a clock with 10:40 on its face. Phil does not come out of his den on his own. He appears to be fully awake. We do not see Phil placed on the ground where he might cast his shadow. The weather that day in Punxsutawney is not specified. If it was foggy or overcast, Phil would make no shadow.

If the forenoon sun is shining, a groundhog could have a shadow. Taller objects cast longer shadows. Groundhogs typically come out of their burrows and sit upright on their haunches to give them a better chance of spotting potential predators. But if Phil is not allowed to be free of his handlers, he never has the opportunity to cast his best shadow. Longer shadows are cast to the west early in the day. At or near noon, however, an animal built close to the ground, like a groundhog, would cast little or no shadow except directly underneath itself where it would probably not be noticed by the animal. In 2009, a club member speaks for Phil from a written script, saying this year Phil saw his shadow; so he predicts six more weeks of winter weather. The video ends without showing whether Phil goes back into his den on his own or not.

One report claims meteorologists find that on any given day at Punxsutawney the temperature tends to be colder if the day is sunny, and warmer if the day is cloudy. So, if Phil does return to his den on his own, is he responding to the cold weather on a sunny day or is he responding to his shadow, or both, or neither? Winter begins on the winter solstice, about December 22, when the sun is in the zenith over the tropic of Capricorn. The first day of spring occurs about March 21 when the sun crosses the celestial equator on the vernal equinox. These seasonal dates are fixed by the motion of the Earth in its orbit around the sun. So spring officially cannot arrive early or late regardless of what Phil thinks.

The Earth’s axis of rotation is tipped at an angle of about 23.5o from a line perpendicular to the plane of its path around the sun. This tilt of the Earth’s axis is the cause of the seasons. On or near March 21, the sun is directly over the equator. This is called the vernal (spring) equinox, and it marks the beginning of spring in the Northern Hemisphere (autumn in the Southern Hemisphere). I have always wondered why a groundhog that sees its shadow would go back into its burrow for another six weeks. March 16, 2009 is about six weeks after February 2. This is five days earlier than March 21 (the vernal equinox). Was this a consideration of those who concocted the story about the ability of groundhogs to predict the beginning of spring weather?

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The most vertical (direct) rays of sunshine reach their most northern point on the Earth on or about December 22. This date is called the winter solstice, and it marks the beginning of winter. Because the Earth’s path around the sun is slightly elliptical rather than perfectly circular, the Earth is actually nearest the sun about January 1 (winter in the Northern Hemisphere), and it is farthest away about July 1. Many people do not realize that Earth’s path is elliptical, and even fewer know that during summer in the Northern Hemisphere the Earth is actually farther from the sun than during the winter.

The temperature inside the animal’s burrow doesn’t change as much as the temperature at or near the surface. About every two weeks during hibernation, groundhogs warm up enough to become sluggishly active for a short period of time to check the temperature outside their burrows. It would be unusual if a groundhog came out on the second of February rather than some other date to check the temperature. They might not come out until March. The terms “spring weather” and “winter weather” have not been adequately defined. Winter weather is not necessarily over just because there is a warm day or two in early February.

There are several other sites in the U.S. and Canada where groundhogs are employed to forecast the weather, but Punxsutawney Phil seems to be the most widely reported by the media. Balzac Billy (Alberta, Canada), Buckeye Chuck (Ohio), General Beauregard Lee (Georgia), Shubenacadie (Nova Scotia, Canada), Smith Lake Jake (Alabama), Staten Island Chuck (New York), Sir Walter Wally (North Carolina), and Wiarton Willie (Ottawa, Canada) are some of the other weather forecasters. It has been reported that these groundhogs correctly predicted early spring weather about 37 percent of the time. For the last 112 years, Phil has predicted 14 early springs (13%). Even if a groundhog makes an accurate weather prediction, it stretches credulity to think that the forecast of a groundhog could apply anywhere other than locally; certainly not across the whole lower 48 states and southern Canada. About half the time, my local TV weatherman on the central coast of California seems unable to accurately predict the weather 24 hours in advance as winter turns into spring. I doubt that his long range forecasting is any better than Phil’s.

Another Animal Prognosticator

There is at least one other animal species that is also famous for its alleged ability to exhibit specific behaviors correlated to the arrival of spring. According to legend and the information promulgated by the city and mission of San Juan Capistrano, northern cliff swallows (Petrochelidon pyrrhonota) begin arriving at the Franciscan Mission of San Juan Capistrano (in coastal Southern California) each year on or about March 19, the Feast of St. Joseph. The 19th is at least one day prior to the celestial first day of spring (vernal equinox) that varies from March 20 to March 21. However, according to sources that may be less subject to biased tourist information, these birds usually return to Capistrano sometime between early February and mid-March. It has been suggested that many people do not see the swallows until about March 19 because they simply have not been looking skyward in expectation until then.

These birds spend the North American winter 7,500 miles south in the “sister town” of Goya, Argentina. Here they fatten themselves on insects, spiders, and worms in preparation for their long migration back to California. They begin the return flight from Goya about February 18 and arrive about 30 days later. They do not eat during these migratory flights and spend about 15 hours during daylight in flight, covering about 450 miles per day. The time of the spring flight varies a few days from year to year.

This species is widely distributed over North America and can be found as far north as Alaska and as far east as Nova Scotia. They also can be found in Central America and in several countries in South America east of the Andes Mountains. These birds do not breed while in their southern latitudes. When the various populations begin their migrations north, they gather into large bands. Their various flight paths coalesce at the southern tip of Central America (Panama-Columbia border), continue along the eastern coast of Central America, cross over the Yucatan Peninsula in Mexico, then fan out in all directions over North America toward their summer breeding territories. The group that settles at San Juan Capistrano flies along the shore of Baja California and enters California through the valley of Riverside. In their home territories, the birds feed voraciously to replace their fat stores, they build their mud nests, mate, lay eggs, and rear their young. Around October 23, the swallows gather into bands again and head towards their various winter homes (such as Goya for the San Juan Capistrano population).

Not all bird species migrate annually over well defined routes such as those for the swallows. Relatively few migratory bird species cross the equator. Migratory species probably assure themselves of a richer and more constant supply of food throughout the year if they migrate to more favorable climates. But what factors trigger the mass migrations of the swallows on (or very near) specific dates? Cliff swallows are difficult to rear in captivity, so other species, such as white-throated sparrows and slate-colored juncoes, have been used for research on their breeding cycles. An organism’s “photoperiod” is the cumulative number of daylight hours to which it must be exposed in order to stimulate specific physiological and/or behavioral responses. The photoperiod of swallows is involved in synchronizing the breeding cycle with the various seasons. Perhaps the amount of fat stored in the bird’s body may be part of the trigger for migration. A bird without a “full tank” of fuel for the long migration probably would perish en route. Although the exact physiological mechanisms have not all been discovered, it seems as though a bird in its southern territory is almost able to “count” the number of hours of daylight, and when a threshold total number is attained, the bird is ready to migrate north.

Although the behaviors of groundhogs and swallows are not the precise predictors of spring weather commonly attributed to them in the popular press, they nonetheless deserve our admiration and respect for their adaptability to survive and reproduce in the face of unfavorable environmental conditions.


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10 Comments »

10 Comments

  1. Joe Hilbig says:

    Re: Punxsutawney Phil and Animal Weather Predictions by William D. Stansfield

    An article such as this gives our detractors enormous ammunition against “skeptics.” The author apparently thinks that people actually believe the whole groundhog/shadow shtick. It’s just fun, William, like Santa Claus or the Easter bunny. You really don’t have to prove that groundhogs can’t predict the weather; we all know that.

    But if you’re going to write a stuffy pseudo-scientific tome, you really should get your facts straight. You have some real boners in your article.

    “At or near noon, however, an animal built close to the ground, like a groundhog, would cast little or no shadow except directly underneath itself where it would probably not be noticed by the animal.”

    That would be true on July 1, but it is not true on February 2. At the latitude of Punxsutawney, at 10:40, the sun would be about 30° above the horizon. A shadow would be 1.75 times the object’s height. I’d say that that’s a substantial shaddow.

    This is a really bad error, William, and one even a child shouldn’t make. School children know that the sun is low in the winter and high in the summer; apparently you don’t! It’s unacceptable that someone who would pass himself off as an expert in anything, could make such a mistake .

    “The most vertical (direct) rays of sunshine reach their most northern point on the Earth on or about December 22.”

    Wrong by exactly 180°. On Dec 22, the sun’s rays are least direct (the sun is lowest elevation) for any given point on earth, and reach the least northern point. On June 20 (this year), the sun is as high as it gets at noon, and reaches its most northern point. At Punxsutawney, the sun will be at around 73°, and an object’s shadow will be very short.

    You could have used the Google to find out that the animal in Nova Scotia is Shubenacadie Sam, and that Wiarton Willie checks his shadow in Wiarton ON, some 600km from Ottawa where you think he performs.

    I would guess that there are other errors in the article, but I no longer trust you enough to finish reading it.

    Shame. No wonder a majority of Americans don’t trust “scientists.”

    Joe Hilbig; 3 Galbraith Cr.; Saskatoon, Saskatchewan (Check with Google Maps).

  2. Chris Miedema says:

    I agree with Joe. This article never needed to be written. I let out a long groan as I got farther into it.

    As a side, Wiarton Willie can be found in Wiarton, not Ottawa.

    M.C. Miedema

  3. Keith Nunn says:

    Count me in on this too. I was quite surprised by this filler piece which is the sort of fluff one might see in a newspaper on Groundhog day, not masquerading as real inquiry.

  4. Donald Prothero says:

    Another thing not mentioned about the swallows: they are vanishing from San Juan Capistrano (where my family lives) because development has wiped out the swampy muddy habitat that breeds the insects on which they feed, and have moved elsewhere. Their required nesting areas, large overhanging structures to which they attach their mud nests, are scattered all over now, and not just focused on the Mission (the only large structure back when the legend started). Nowadays when San Juan Capistrano holds its big swallow festival, the place is crowded with people who identify EVERY bird as a “swallow”, while there are actually almost no real swallows to be seen.

  5. R. J. Allen says:

    Glaring errors should never have gone so far as to be printed. I caught the

    “The most vertical (direct) rays of sunshine reach their most northern point on the Earth on or about December 22.”

    error right away, but missed the “Shadow” error. I guess it was because I took the whole article as humorous. No one makes a career debunking Santa, or the prognosticating earthworm (I made that up!). I did learn a few things (the earth is most distant from the sun on July 1st – I thought it was the summer solstice – June 21st). By the way, I am a scientist (chemist), and am surrounded by people who believe we didn’t land on the moon (until I convinced him otherwise) and too many who believe that the Bible is the inerring word of a god…Yes, hard to believe! These people are very critical thinkers for work related matters but when their critical skills could serve them best, become banana slugs (with all due respect to the slug population).

    “One would not be a successful scientist without realizing that, in contrast to the popular conception supported by newspapers and mothers of scientists, a goodly number of scientists are not only narrow-minded and dull, but also just stupid” James Watson, The Double Helix. (see Skeptic Vol 9 No2, 2002).

    Unfortunately we’re self-concious naked apes, with nukes, in a time where we are still saddled with religion.

    Peace,

    Bob

  6. Eugene says:

    I logged in with the intent to point out a small (very small) litany of errors, only to find the bulk was already addressed by other astute cyber readers. As a regular passerby through Wiarton, Ontario, I’m glad.

    I am a biologist on the day job, as I believe the author is. However, I have always regarded photoperiod as referring to the amount of light over the course of a day to which an organism is exposed, not “the cumulative number of daylight hours to which [an organism] must be exposed in order to stimulate specific physiological and/or behavioral responses.” The semantic difference is subtle, but real. In other words, I don’t conceive of “photoperiod” as a property of an organism (e.g., I do not think of the “photoperiod of a swallow”), but rather think of photoperiod as a property of the environment (independent of organisms in definition) that can happen to trigger various organismal responses.

    …And I didn’t find Murray’s mannerism to involve any noticeably intense ocular focus in Groundhog’s Day.

  7. Kennypo65 says:

    I live in western Pennsylvania, so I grew up with Punxatawney Phil’s “predictions” every year. Of course it’s crap, but it’s fun crap. It also brings attention and tourist dollars to a lovely American small town. So what’s the big deal?

  8. Mark says:

    The groundhog day dissection is one of the most pointless rants I’ve ever read on this site. Most of the supporting information is completely irrelevant to the topic; it reads like an Intelligent Design article throwing out a series of facts that – while more or less true – do little to support the author’s case. The section on swallows isn’t bad.

  9. DC says:

    I feel like such a dupe, after 50 years of planning my spring vacation based on the Ground Hog. And why didn’t I know about all the other ground hogs that disagreed with Phil? Another failing of the main stream media, refusing to cover the story; and another failure of schools, refusing to teach the controversy.

  10. Alex says:

    “These seasonal dates are fixed by the motion of the Earth in its orbit around the sun. So spring officially cannot arrive early or late regardless of what Phil thinks.”

    The “Official” first day of any season is a myth – there has never been a decree by any governing body stating that the first day of spring is on the vernal equinox. The seasons are actually, by nature, quite unofficial and their starting dates vary from country to country even within the same hemispheres and weather systems.

    Yet somehow every calendar lists the “official” start dates, but no reference is ever given to the officiating body. The groundhog’s “interpreters” seem as good of an authority as anyone!

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