Most good hatcheries will put off the shipping date if it is too cold to ship. If you didn't order enough then expect to receive "packing peanuts" along with your order for warmth. Packing peanuts are either males or straight run of chicks that they were not able to sell. Warm up the brooder the night before you are expecting them and make sure the hatchery has your phone number. I used Ideal and they put my phone number on the box so the post office could call me when they came in. Depending on your area, you may get a really early call. I live in a small town and pick mine up at 4:30am. You may also want to call or stop by your local post office and give them your number as well just in case. Rural post offices are more likely to have warming stations for the chicks but many post offices do not so it is important that you pick them up as soon as possible. Sometimes chicks do pass due to stress of shipping so I suggest to add vitamins to their water for the first day or so to combat this. I have never lost a chick after giving them vitamin or sugar water. I have also not lost a chick during shipping, the time to loose any is in that first day at your house. Good luck!
