During the 1939 season 95 ground squirrels and 4 Allen chipmunks were taken in live traps in the rim area. Ninety squirrels were released (many squirrels were retaken and released several times) and 5 squirrels were kept captive for observation of their winter behavior. The data that might be expected to accrue from this procedure are:

The age distribution and sex ratio.
The population density in the area examined
The winter survival rate.
The foraging area of individual squirrels.
The special distribution of young of the year after they leave the mother's burrow.

Although the returns from this project are for the most part purely ecological there is the possibility of some practical utility should the squirrels, as has happened elsewhere, become infected with some communicable disease which would require their elimination from a give area. A proof that they are not migratory would greatly simplify the eliminative procedure.

METHODS

Squirrels were taken in wire box traps obtained from the National Live Trap Co., Tomahawk, Wisconsin, and rewired to hold squirrels. They were marked by cutting hind toes for numbers 1 to 10 (toes cut in order from left to right), and by cutting front toes in order from left to right for 10 to 20, etc. Correspondence on the subject had elicited the information that ear tagging with metal tags is unsatisfactory because the tags come out. Cut toes were disinfected with 70% alcohol and did not appear to cause the squirrels any considerable inconvenience although some swelling of the cut digit could be observed and squirrels occasionally were noted to be favoring the foot in question for a day or so after the operation. However since many squirrels were seen foraging as usual within an hour after release and as no squirrel was retaken with an obviously infected foot the method seems to have been a good one.

The data are presented in tabular form.

ASSEMBLED DATA

Age and sex of trapped squirrels

Reproduction in terms of the season as determined by lactation of adult females

Number of times squirrels were retaken

SUMMARY

1. Seventy-three squirrels were trapped between the Crater Wall Trail and the Lodge in a strip of territory about 150 feet broad. This represents a very dense population.
2. Squirrels do not, in a season, move around much. They may repeatedly be taken in the same territory, rarely are found more than 100 feet away from it.
3. The sexes are equal in number in the population; an excess of young males balances an excess of old females. This is the situation to be found in other rodent populations such as the deer mouse.
4. All young squirrels taken in the vicinity of a mother's burrow were found to have traveled only a short distance away after weaning. This is a tentative inference and awaits further trapping data.
5. Young are born during the months of June, July, and August and emerge from the mother's burrow during July, August, and September. At the Rim Area in 1939, the first newly emerged young were seen July 15th and the last September 20th. A lactating female was taken as late as August 24th. In 1938 the first young were noted in the Rim Area on July 31st and the last on September 15th. This seems to suggest that occasionally a mother may have a second brood.