First off, Welcome to BYC!!! We're happy to have you!
At only 5 months old, they wouldn't be molting; however, this is nothing to be worried about! Since you just got them last Friday, they are no doubt still adjusting to their new home, which is likely stressful and can lead to feather loss. This feather loss should decrease in the coming weeks as they become accustomed, both to their environment and each other.
A few questions to ask yourself about helping reduce stress:
- Is your flock receiving a balanced diet? (Proper feed & available oyster shell and grit)
- Are they over-crowded? (~4 feet per chicken inside the coop, and about double that in a yard/run)
- Is there routine? Or is their daily routine being disturbed by predators, loud noises, or other external influences?
If they are still loosing feathers after an extended period of time, you may want to look into checking for lice/mites or seeing if they are pecking each other.
For treating lice/mites:
For treating feather pecking:
Hope that helps! And congratulations on your new flock!!