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MATURATION OF REPRODUCTIVE BEHAVIOR 
AGE IN DAYS 
Figure 150. — Maturation of reproductive behavior. This index, P 2 , as defined in the text, is the product of the proportion of 
parous females times the proportion of these which successfully rear litters. It assumes that the failure to reach 1 .0 at earlier 
ages relates to environmental disruptions of learning or innate behaviors in the realms of relationships between the sexes, 
or of maternal behavior. 
there dig a new burrow, or if she chooses to 
remain at an established burrow she must be able 
to express sufficient territoral behavior to exclude 
her associates from the cavity where she will have 
her young. Then during the critical first 4 days 
after parturition she must not only nurse her young 
but refrain from eating them. During their first 
2 weeks of age the young have a better chance of 
survival if the mother inhibits entrance by other 
adults, and if she plugs neighboring entrances 
providing access to her section of the burrow. 
From birth through at least the third week of life 
the mother must express adequate retrieving be- 
havior. This enables her to change residence when 
danger threatens her young. And if they should 
wander outside the nest, as they certainly can 
from 12 to 21 days of age, before they are able to 
acquire their own food other than from nursing, 
the mother’s failure to retrieve would certainly 
lead to the death of the young. Lastly, the mother 
must provide a cache of food adjacent to the nest 
so that weaning to solid food may proceed during 
the fourth week of life without the young having to 
go exploring prematurely. 
269 
