This paper is presented here with the consent of Vagn Flyger, the author, a professor emeritus at the University of Maryland.
THE 1968 SQUIRREL "MIGRATION" IN THE EASTERN UNITED STATES
By Vagn Flyger
Natural Resources Institute
University of Maryland
College Park, Maryland 20742
Contribution No. 379
Paper to be presented at the Northeast Fish and Wildlife Conference, White Sulphur Springs, West Virginia, February 1969.
The 1968 Squirrel "Migration" in the Eastern United States
During September of 1968 gray squirrels (Sciurus carolinensis) showed unusual activity throughout portions of the eastern United States from Vermont to Georgia. The first reports of anything unusual came from a colleague who drove from Maine to Maryland on September 13th and, along the way, noticed a large number of dead squirrels on the highways in southwestern Vermont and eastern New York State. At the same time, an article in the Asheville, North Carolina CITIZEN of September 15th reported hoards of squirrels emigrating from Maggie Valley, North Carolina because of a food shortage. This was followed during the next two weeks by other newspaper accounts of vast mass migrations, mass starvation, and unusual activities such as swimming lakes, damaging farmers' crops, or entering areas where they had previously been absent.
Information concerning the squirrel "migration" was picked up by the Smithsonian Institution's Center for Short-Lived Phenomena which promptly notified me. The Center expended every effort to keep abreast of all the happenings and maintained a continuous survey of newspapers in addition to making telephone calls to biologists, game wardens, and other interested people throughout the East. I was kept informed by daily phone contact with Robert Citron, Director of the Center. Joseph S. Larson of the University of Massachusetts personally investigated the New England-New York State area for unusual activity and alerted biologists in that area.
I drove to North Carolina and spent the week of September 22nd through the 28th in the Western North Carolina-Eastern Tennessee area. Upon arrival in the area, I contacted the local game protectors and biologists who took me to areas of squirrel activity. I later contacted the Southeastern Cooperative Wildlife Disease Study at the University of Georgia, and a team of biologists was dispatched by Frank A. Hayes to help in the investigation. This team consisting of Lawrence Andrews, James Smith and Martin Perry arrived on September 26th. We set up a laboratory in a motel room in Boone, North Carolina for the examination of squirrel specimens. Game protectors shot 11 squirrels in western North Carolina and 5 in eastern Tennessee which were examined together with fresh road kills in the laboratory. Some of the material was preserved and taken back to Athens, Georgia for more detailed analysis.
On October 9th I drove to Delmar, New York to pick up squirrels collected by New York State biologists and also discussed the recent squirrel activity with C. W. Severinghouse, Joseph Dell, Joseph S. Larson and others.
FINDINGS
During September of 1968, squirrel activity in portions of eastern United States was unusual and spectacular enough to be noticed by sportsmen, motorists, and farmers as well as game wardens and biologists. Local newspapers, radio and television stations reported the activities but greatly distorted the situation; some going as far as to advise people to feed squirrels. Signs in supermarkets and elsewhere gave similar advice in the North Carolina area, and some people responded by sending checks to the North Carolina Game and Fish Department to help pay for squirrel food and requested that the department undertake a squirrel-feeding program immediately. Enterprising Tennesseans organized volunteer Florida residents to gather acorns for shipment to Tennessee. Sportsmen requested that the North Carolina and Tennessee Game and Fish Departments open the squirrel seasons early and double the bag limits, and indeed this was done by the Tennessee Game and Fish Commission.
The number of dead squirrels on the highways was spectacular. For example, Mr. C. M. Teseneer, Game Protector, reported 28 dead squirrels on a 22-mile stretch of highway, over 100 dead squirrels on an 80-mile stretch, and 100 dead specimens on a 27-mile stretch -- all near Asheville, North Carolina. On September 24th, I counted 48 dead squirrels on a 32-mile stretch of road near Asheville. Wildlife Protector Thomas Osborne of Boone counted 50 squirrels on a 5-mile stretch of road near his home on the 18th of September. Other people made similar reports (Citron, R., 1968). Game Protectors Wade Cram and Wayne Beard commented that in addition to many dead squirrels found on the road, they noticed more dead foxes than usual on the highways, probably because the foxes, initially attracted by the squirrel carcasses, were in turn killed by automobiles.
Another instance of unusually high numbers of dead squirrels on highways was reported by Larson (1962) where the number of dead squirrels seen during September of 1960 ranged from one to five per mile on the Massachusetts Turnpike. To give some idea of how much the squirrel activity during September 1968 differed from ordinary conditions, I made the following rough calculations. I drive an estimated 30,000 miles every year throughout the state of Maryland, and over 14 years this amounts to 420,000 miles. The number of squirrels picked up (including those brought in by colleagues) amounted to 105 specimens during this time. Of course, I saw more than this number of squirrels on the road but was unable to stop often because of traffic conditions or for other reasons. However, the number of squirrels picked up is one for every 4,000 miles or more. If by conservative estimate I was able to pick up one out of four (I picked up more than this), this means that the road kills in North Carolina exceeded the normal road kill by a factor of more than 1,000. Road kills are often indicators of mammalian activity, and whenever the number of dead squirrels on highways exceeds an average of more than one per ten miles, it can be assumed that some sort of unusual activity is taking place.
Various observers reported squirrels both swimming and drowned in TVA reservoirs in the North Carolina-Tennessee area, and unusual numbers of drowned squirrels were also reported from the Hudson River in New York State (Smiley, 1968). Eighty dead squirrels were taken from the raceway at Cheoah Dam and an additional 37 specimens were collected a week later in the same spot.
The squirrels found dead on the road and those found drowned in the reservoirs of North Carolina and Tennessee had a sex ratio of 63% females and 37% males. Ninety percent of the animals were subadult, i.e. animals from the February-March litters. In contrast, the sex ratio for New York State animals was essentially equal, and 65% of these squirrels were subadult. Only one animal (a New York State specimen) of those examined was from the July-August litter. These data differ considerably from the usual sex and age ratios found in road kills collected during the past 14 years where 61% of the animals are males and the age ratio is 4% immatures, 19% subadults, and 77% adult animals. Unfortunately there is not enough data to break this down by seasons for comparative purposes (Table I).
The examination of these squirrels showed no unusual pathological conditions nor an abnormal number of parasites (Andrews, 1969). The parasites found by the Southeastern Cooperative Wildlife Disease Study included:
Bohmiella wilsoni
Rictularia sp.
Citellinema bifurcatum
Heligmodendrium hassalli
Eimeria sp.
Neohaematopinus sciuri (louse)
Microfilaria
Cysticercus (prob. Taenia pisiformis)
Trichostrongylus sp.
Sarcocystis sp.
Orchopeas howardi (flea)
Ixodes texanus (tick)
The ecto-parasite infestation was considered light. Game Protectors Wade Cram and Wayne Beard commented that many squirrels which they had rescued on the Fontana Reservoir seemed to have numerous "flea bites" on their ventral sides. I, too, observed this on some of the specimens; possibly these were chigger bites. Conceivably, squirrels moving about a great deal on the ground would be subjected to more chiggers than those not engaged in such activity. However, we were unable to determine the precise cause of these spots.
None of the squirrels examined in the laboratory (about 30, including 16 collected by shooting) appeared emaciated or gave any indication of being in poor condition. Some animals were infested with warbles (Cuterebra) but there was no indication that the squirrels were either under any form of unusual stress or trying to escape areas of high population density because of intraspecific strife. The food supply was certainly adequate to feed all of the squirrels at the time of the unusual activity, and many of them were fat with stomachs containing black cherries and acorn mast. Dogwood trees in the area were heavily loaded with berries (a food not buried by gray squirrels) but the food supply would not have been enough to last throughout the winter.
In discussions with knowledgeable observers in the area there was almost total agreement that the entire activity took place during the month of September and that the peak was somewhere in the middle of the month. Newspapers, administrators and others not in the field were usually not up to date on the activities and assumed that the "migration" was at its peak when actually it had occurred the week before.
The behavior of squirrels during September seemed unusual according to many observers. Squirrels appeared in areas where they were not usually seen, and one man commented on the "dancing" of squirrels on the highway. As cars approached, squirrels on the road would sometimes jump into the air, zigzag back and forth, and behave erratically. I also observed this. One man explained this by saying that the migrating squirrels had traveled so far that the soles of their feet were very thin and therefore they felt the vibrations of approaching cars, and the tickling sensation made them jump into the air. A more likely explanation is that emigrating squirrels caught out in the middle of the road were unfamiliar with the area and, not knowing which way to run, behaved erratically because they were terrified and confused.
EXTENT OF SQUIRREL ACTIVITY
Additional information on squirrel activities can be obtained from the November 4, 1968 Report of the Smithsonian Institution's Center for Short-Lived Phenomena.
Vermont - One observer noticed an unusual abundance of road-killed squirrels on September 13th (Davis, 1969).
Connecticut - Two observers related unusual numbers of dead squirrels on the Merritt Parkway on September 9th (Davis, 1969; Andrews, 1969).
New York State - Many reports of dead squirrels on highways and squirrels drowned in the Hudson River (Davis, 1969; Smiley, 1968; Chambers, 1969; and others). The New York State Conservation Department collected 122 specimens on highways from the Hudson River south of Albany.
Pennsylvania - A few reports of unusual numbers of dead squirrels on highways (Chambers, 1969; Lindsey, 1968).
Maryland - No unusual activity or road mortality reported.
New Jersey - A report of some activity along the Delaware River on the Pennsylvania border.
Virginia - No unusual activity or heavy road mortality reported.
West Virginia - No unusual activity or high road mortality reported.
North Carolina - Many reports of dead squirrels on highways or drowned in reservoirs in the western portion of the state.
South Carolina - A few reports of unusual numbers of road kills. Georgia - Numerous reports of activity in the northwestern portion of the state.
Tennessee - Much activity reported in the eastern portion of the state.
Kentucky - An abundance of squirrels but no indication of unusual activity.
Florida - No unusual activity but the acorn crop was good.
DISCUSSION
Squirrel "migrations" occurred during recent historic times and have been described by Seton (1920) and Schorger (1949). These "migrations" occurred almost invariably during September and Seton believed them to be caused either by psychological factors or an overabundance of fleas. September is the time of year that food is most abundant and therefore food shortage did not seem to be a likely factor in the cause of these "migrations".
As the forests of eastern North America were cut in the late 1800's, gray squirrel "migrations" became less frequent and on a smaller scale; during the last 100 years they have become relatively rare. The reason why these "migrations" occur especially during the month of September when food conditions are at their best has been puzzling. Squirrel "migrations" occur unannounced, and by the time a biologist arrives on the scene to investigate the situation, the event has usually ended. As far as I know, this is the first "migration" that has received much attention by biologists. An interesting and detailed account of this "migration" was published in mimeographed form by the Smithsonian Institution (Citron, R., 1968).
The gray squirrel does not cache food in the manner of the red squirrel (Tamiasciurus hudsonicus) which stores large amounts of seeds or nuts in tree cavities or elsewhere. Gray squirrels, however, do store food and during September can be seen gathering acorns and burying them individually beneath leaves and in the soil (Seton, 1921). At this time of year, gray squirrels also take part in what is called the "fall reshuffle". Studies involving marked squirrels have shown that at this time of year squirrels may move about and take up residence in new areas (Brown and Yeager, 1945; Allen, 1952).
The reason for these activities may possibly be explained as follows: during the late summer and early fall gray squirrels are active burying nuts and acorns; if at this time, squirrels do not find enough acorns or nuts to keep themselves occupied they move elsewhere looking for such a supply; if and when an adequate supply of acorns is found, the squirrels devote much of their time and energy to burying these individually and in so doing become acquainted with the surrounding area where they take up residence. In this process they have made a scattered cache of nuts and acorns which will help them during the winter months when other foods are scarce. This probably accounts for the "fall reshuffle" when squirrels in an area where late summer food is not abundant may move about until they find such food and in the process of burying it find a new area in which to settle.
Based upon discussions with many individuals as well as upon my own observations, 1967 was a year with a bumper acorn crop; 1968 in contrast was an unusually poor year for acorns. Squirrel numbers, at least as far as Maryland hunters were concerned, were low in 1967 but high in 1968. This increase in squirrel numbers from one year to the next is a possible result of the heavy acorn crop which resulted in low winter mortality and increased reproductive success during early 1968.
During September of 1968 an unusually large number of squirrels was present in most of the eastern United States, possibly resulting from the successful reproductive season following the 1967 excellent crop of acorns. Biologists from a number of the states as well as sportsmen have reflected on the high number of squirrels present in 1968. A great number of squirrels, largely from the February-March litters, found few acorns and nuts to bury; they kept moving, and the few acorns they did find were quickly buried compounding the situation so that more squirrels were moving about much more than usual.
There were no indications that the movements of squirrels were directional except over lakes. I encountered no one who had seen mass directional movements, but of the 14 squirrels which I saw swimming across North Carolina reservoirs, 13 were swimming north. These reservoirs, with their long axes running east and west, are the southern boundaries of the Great Smoky National Park. The elevation of this park is greater than that of the surrounding area, and the park vegetation runs more to northern hardwoods and evergreens. Therefore, it is relatively less desirable for gray squirrels and better suited for red squirrels; the park would probably have lower gray squirrel densities than would be found in the neighboring forests. Assuming that the squirrel density south of the lakes was high and squirrels were moving in all directions with no overall pattern or directional movement, an observer watching swimming squirrels would think that a mass northerly movement was taking place. Assuming that few squirrels occur on the north side of the lake and that animals would always swim across in the most direct manner, there would be few squirrels swimming the lake in a southerly direction or any direction other than north (Fig. I).
Messrs. Cram and Beard made the interesting observation that in their rescue operations of gray squirrels swimming the reservoirs, they could not persuade the swimming squirrels to turn around and swim back to where they came from. Possibly swimming squirrels had their attention fixed on some aspect of the far shore and headed for that.
No other suggested explanation for squirrel movement seems to be consistent with available knowledge. Theories involving stress and starvation are untenable and parasites do not seem to be involved. Fleas which were considered to be one of the possibilities by Seton do not seem likely because fleas were not as common as they usually are. Possibly the preponderance of females could be accounted for in the North Carolina animals by the fact that gray squirrel males are more active (Flyger, 1960) than females and start moving earlier. Had the investigations been initiated earlier perhaps a larger proportion of males would have been found. More data is needed on this aspect.
Squirrel emigrations may serve a valuable function in the evolution of the species as a factor in genetic adaptation. Prior to the time of heavy cutting by civilized man of the forests of eastern United States, the gray squirrel occupied an almost continuous distribution over that portion of the United States east of the Mississippi and several hundred miles west of this river. During periods between mass movements, local squirrels (in common with other organisms) undergo mutations and the pressures of selection according to local conditions. When a large number of squirrels move about, these mutations plus new combinations of genetic characters are spread about in the range of the species. In so doing, additional recombinations of genetic characters are brought about permitting selection to operate on the new combinations. Because of the great number of genetic characteristics present in most organisms the number of combinations and recombinations within an animal such as the gray squirrel approaches infinity, and in this way selected pressures are able to work on the general characteristics which make the animal most highly adapted to the general conditions of its range. In areas where squirrels occupy small habitats, such as parks, islands or small woodlots, it is to their advantage to adapt to local conditions and not fluctuate greatly in numbers or partake in mass movements. For a small population to fluctuate wildly in numbers would threaten the local population with extinction because the number could become too low to recover. Local races develop specifically adapted to local conditions. Probably these factors account for the aberrant coat colors which are found in so many small local urban populations of squirrels in a high proportion of the population.
The fox squirrel (Sciurus niger) occupies small woodlots such as the oak openings of the Midwest and habitats along rivers and streams. It does not fluctuate greatly in numbers nor partake in mass movements as do the gray squirrels; possibly for this reason, many varieties or subspecies of fox squirrels exist compared to gray squirrels.
During historic times, before the virgin timber of North America was cut for man's use, squirrel migrations occurred from time to time and were documented by Seton (1920) and Schorger (1949). Since the late 1800's these mass movements have become rare and minor in extent, but it is tempting to speculate that with the current return of forests mass migrations may increase in frequency.
RECOMMENDATIONS
Squirrel migrations are poorly understood and should be investigated in greater detail to determine their causes. When such an eruption of squirrels occurs, it does so quickly and without warning. Field personnel should be alerted to the possibility of such occurrences especially during September and encouraged to report any unusual activity immediately by telephone to the Smithsonian Institution's Center for Short-Lived Phenomena. The telephone number is 864-7910, Area Code 617 [THIS IS A 1968 TELEPHONE NUMBER]. If reports go through normal channels, by the time the interested biologist hears about it the event may be over.
Game departments can be caught unawares by a squirrel eruption because hunters may demand an earlier opening date for the season and an increased bag limit without the department's being aware of the facts. If commission members are unaware of what is happening, they cannot act upon the request until they gain more knowledge and have time to think about the matter. For this reason, field personnel should also alert their administrators immediately upon learning of unusual squirrel activity. However, if a region has an unusual abundance of squirrels in the late summer of any one year and a poor mast crop at the same time or if a "migration" takes place, it is suggested that consideration be given to increasing the squirrel harvest because the large number of squirrels present during late summer will consume most of their winter food supply resulting in a severe winter mortality and a lower squirrel population the following fall. Here is a case where increased harvest produces an increased number of squirrels - i.e. the hunters can have their cake and eat it too.
TABLE I
Sex and Age of Road-Killed Squirrels
New York State (includes drowned specimens)
September 1968 Unknown Age Immature Subadult Adult Total
Males 21 1 17 12 51
Females 27 0 17 6 50
Unknown Sex 19 0 0 0 19
TOTAL 67 1 34 18 120
North Carolina - Tennessee (includes drowned specimens)
September 1968
Males 16 0 2 4 22
Females 23 0 14 0 37
Unknown Sex 1 0 0 0 1
TOTAL 40 0 16 4 60
Maryland
All Seasons - 1954-1968
Males 2 1 8 42 53
Females 1 2 8 23 34
Unknown Sex 0 0 0 0 0
TOTAL 3 3 16 65 87
GRAND TOTAL 267
BIBLIOGRAPHY
Allen, John M. 1952. Gray and Fox Squirrel Management in Indiana. Indiana Dept. of Conservation. P-R Bulletin No. 1. 112 pp.
Andrews, Lawrence. 1969. Personal Communication.
Andrews, Lawrence. 1968. Necropsy report on gray squirrels collected in North Carolina and Tennessee in October 1968. Southeastern Cooperative Wildlife Disease Study. Mimeo.
Brown, Louis C. and Lee E. Yeager. 1945. Fox Squirrels and Gray Squirrels in Illinois. Bull. Illinois Natural History Survey 32(5):443-536.
Chambers, R. E. 1969. Observation and opinion on highway mortality of squirrels - Fall 1968. Unpub. ms.
Citron, Robert. 1968. Smithsonian Institution Center for Short-Lived Phenomena. Appalachian Squirrel Migration, Appalachian Mountain Areas Event Report.
Davis, Robert M. 1969. Personal Communication.
Dell, Joseph. 1969. Personal Communication.
Flyger, V. F. 1960. Movement and home range of the gray squirrel, Sciurus carolinensis, in two Maryland woodlots. Ecology 4(2):365-369.
Larson, Joseph S. 1962. Notes on a recent squirrel emigration in New England. Jour. Mamm. 43(2):272-273.
Schorger, A. W. 1949. Squirrels in Early Wisconsin. Trans. Wisconsin Acad. Sci., Arts & Letters 39:195-247.
Seton, E. T. 1920. Migrations of the gray squirrel (Sciurus carolinensis). Jour. Mamm. 1(2):53-58.
Seton, E. T. 1921. Gray squirrels and nuts. Jour. Mamm. 2(4):238-239.
Smiley, Daniel. 1968. Gray Squirrels on the Move. The Chirp 15(11):1-2.
Mimeo.
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