Vol. 22, No. 12 
Page 2 
Ecology and Management of Sguirrels Nixon, 
L. P. Hansen 
Within unexploited populations of fox squirrels, the survival of young squirrels 
is typically quite low; fewer than 30% of those born are still in the population 
6 months later. From the number of females known to have nursed young each year, 
we presume many juvenile squirrels die or disperse shortly after weaning, for they 
are never captured in livetraps. 
We base this conjecture on the fate of those squirrels ^4 months old that 
we have been able to mark. These squirrels were found to have a significantly 
reduced survival interval (P<0.001) compared with squirrels first marked at 
4-6 months of.age. Apparently only those juveniles who are able to compete with 
the older squirrels for food and den sites remain to breed. 
We believe most of these "lost" juveniles emigrate shortly after weaning in 
response to aggressive interactions with older squirrels. Such dispersal, defined 
as the distance from birthplace to breeding site, has obvious advantages for the 
species, despite the high rate of mortality associated with movement into strange 
areas. 3 
One advantage to a fox squirrel population is the ability to regulate density 
e ow carrying capacity, defined here as an evolutionary response to long term 
average levels in food abundance. Fox squirrels have never been reported to have 
experienced the large scale migrations so evident in gray squirrels in the ]8th 
and 19th centuries in the midwest. A lack of large scale migrations suggests 
that fox squirrels are more capable of regulating their abundance than are gray 
squirrels. a ' 
h^-* D ! SperSa a,so a,lows fox squirrels to spread their range rapidly as favorable 
abitats are created and to quickly reinvade areas that may have been depopulated, 
such as overhunted woodlots. Such a range extension began almost as soon as 
w ite settlers began clearing the virgin forests of the midwest. The presettle¬ 
ment range of the fox squirrel was the prai reforest edge centered in the 
Mississippi Valley. Yet by 1900, this species had invaded all of Illinois, 
Indiana, and Ohio and most of lower Michigan. As trees wee planted in the short 
grass prairie of the west, the fox squirrel moved wetward and has now reached 
the foothills of the Rocky Mountains in Colorado. 
Re sponses of Prairie Chickens to Habitat Manipulation R. L. Westemeier 
Last month's newsletter (MWRL 22(ll):3-4) discussed prairie restoration and 
the apparently increasing use of and increasing nest success in prairie grass by 
prairie chickens on the Bogota Study Area. Also, nest densities and nest success 
w r compared for 4 categories of prairie management: (1) no disturbance, (2) 
nwwing for weed control, seed, or nesting enhancement, (3) haying, and (4) fresh 
burn Among these categories, mowing for weed control, seed, ousting enhance- 
ment showed the best results. y 
and 2 Sh ° WS 3 f " rther r breakdown of these data. Prairie chicken nest numbers 
and nest success are shown for burned and unburned fields dominated by prairie 
grass according to the nest season after prescribed burning and according to the 
