Vo 1. 18, No, 9 
Page 3 
Ecology and Management of Sguirrels 
C. M. Nixon, 
S. P, Havera 
In previous research letters we have reviewed the problems encountered in 
attempting to determine the direction and magnitude of annual changes in the 
statewide squirrel population (see MWRL 17, Nos. 7, 8 , 9 , 11 , 12). 
Use of midwinter squirrel counts, previous harvests, and low temperatures 
in spring failed to provide any consistent or significant correlations with the 
subsequent squirrel harvest. 
The basic assumption is that the size of the squirrel harvests and the 
midwinter squirrel counts are annually dependent on squirrel abundance and thus 
are valid indices of squirrel abundance. If both indices are valid indications 
?In q ^ r : e, , ab ^ danC n. then We W ° uld expect them to be correlated with each other. 
Failure to find significant correlation suggests that either one or both indices 
ay not be valid for Illinois. Both the harvest estimate and the midwinter 
^ S hfc?° nta '£ Ser,ous fai >jngs and there is no way of knowing which index is 
h(a .. 1 °? e f ° r , use m 111ino,s * We have recommended that the midwinter census 
be discontinued because we can suggest no practical means of improving this 
census without greatly increasing costs. Studies have shown that time-area 
counts like the Illinois midwinter census have not proven to be accurate when 
tested against more intensive census techniques, such as 1 ivetrapping. 
We have also recommended use of several techniques to improve estimates of 
Deoartment f r rV6St (S “ T* ,7(,2):2 - 3 >‘ The S^vey a "d Inventory Project, 
Department of Conservation, has begun to modify its procedures for sampling 
0 U ^ rS by questionnaire, using preseason notification of hunters and repeated, 
thl IT t0 ,ndUCe nonres P onde "ts to reply. In at least one year, 
considered t0 ^ vlrtua,, y nonrespondents should be 
considered so that the entire sample of selected hunters could be used to 
determine the squirrel harvest. If suitable means are used to sample squirrel 
hunters, we expect the estimate of the state-wide harvest to decline drastica ly 
perhaps as much as a million squirrels below present harvest estimates ^ 
n. o '; lna ! ,y i !f have rec0fT| mended that the Survey and Inventory Project, 
and 3 ^ Conservat '° n ' be 9 *n to monitor tree seed crops, squirrel harvests, 
and sex and age ratios of squirrels on a selected sample of public hunting 
areas scattered throughout Illinois. P nunting 
the f ° reSt !' Studies have co nfi™ed a relationship between 
fcarvl LnV / ! eed u Cr ° P ' Chlef,y ac0rns ^ ercus S PP-) a " d hickory 
s f sec iuent squirrel reproduction, condition, and density. 
r smaller forests often surrounded by agricultural crops, the 
a ^! .° a mast shor tage are much less severe. It was determined in fowa 
harve^' 9a n T* did n0t a,wa y s affect subsequent squirrel 
^ ^ 80 h t tud ' eS conc,uded that the availability of agricultural crops 
provided squirrels with sufficient food during years of poormast production! 
