Female rabbits typically pull out their fur due to an increase of estrogen levels during pseudopregnancy, prompting them to carry out maternal behaviors such as building a nest. This stage of the pseudopregnancy (release of ova prior to gestation), which usually occurs between 15 and 18 days after ovulation, is accompanied by a loosening of fur.
The loosening of fur makes it easier for female rabbits to pull it out, generally from the abdominal and shoulder areas within reach.
During this nest-building period, female rabbits will tend to collect whatever materials are available and carry them to a nesting point. These might include hay, paper and even fur.