I'm not going to defend the behavior you are describing. It's simply wrong to be mean. We all know that.
However, I am going to try to explain at least a little of it -- because some of you are wondering "why" people behave that way. As a very experienced NICU nurse who is now in staff development and teaching people about horizatal hostility and relational aggression, here are my thoughts on the "why."
1. Experienced nurses have seen many new nurses "come and go" over the years. Many have probably precepted and mentored many new people over the years. Early in their careers, they may have been very welcoming and nice to the new people. However, over time, they have invested much of their emotional energy welcoming new people into their unit who have not stayed for one reason or another -- and not necessarily because of having been treated badly. Many leave because their husbands get transferred, or they have a baby, or they decide that the patient care is too stressful for them at this stage of their career, or they don't like the hours, or they go to grad school, or they only took the job to get the training and always planned on leaving after a year regardless, etc. etc. etc. Anyway ... after a few years, some of the experienced nurses get burned out from having invested so much of their emotional energy into the orientation of these folks year after year. So, they begin to take a "wait and see" attitude. They think, "Let's see if this person has what it takes to be successful and is going to stay a while before I invest emotionally in helping her. I can't keep giving and giving to people for whom the investment is not going to pay off." I'm not saying it's right ... I'm just saying that's part of the explanation. Don't take it personally. Once they see you are competent and are planning to stay for a while, those folks may very well start to be much more helpful and friendlier.
2. When people are frustrated in their personal lives or in their jobs, they often don't know how to deal with that frustration productively. Rather than address the sources of their frustrations directly, they just become grouchy and crabby in general. The vulnerable people in their environment (secretaries, nursing assistants, orientees, etc.) bear the brunt of their grouchiness. Again, it's not right -- but it's nothing personal against you. As you establish your competence in the unit and develop a reputation as being a good nurse to have around, you become less vulnerable and less of a target.
3. Many people, especially women, grew up using relationships and social interactions as a means of controling their environment and maintaining their self-esteem. By being "queen bees," they bolster their inner sense of self-worth and maintain a sense of being in control in a world in which they often feel out of control and vulnerable themselves. In many cases, it is the same behavior we see amoung 12-year olds continued on into adulthood. "If you become friends with that new girl, I won't be your best friend anymore." There are cliques, and gossip, and social climbers, and cat-fights, etc. just like in junior high. For some women, maintaining the social order in this way is the only way they know how to be in the world with other women -- because this has been their social reality since they were children. Researchers have found that even girls under the age of 5 use social relationships in this way. Little boys compete openly and directly with each other and remain friends as they compete for sports victories and social status. Little girls often use their social skills to manipulate relationships to gain status.
As I said above, I am not justifying the bad behavior ... but maybe some people will be helped by understanding it a little better.
Good luck to you all.