I have ducklings between 3-2 weeks old, what age can you place them outside safetly. Once they start to feather? I am in northern NJ and its been in the mid 60s-70s during the day and low 60s at night. Lot of rain though. Do I need a heat lamp in there with those temps? I am looking forward to putting them in their pen, cause they are making a mess inside...lol.