Hi Robert,
This is a worry. Unless its an obvious cause like its really hot where you keep them which would make them breathe fast, then I think they are sick. Respiratory diseases in birds can have a variety of causes from parasites or other infectious causes. Keep their environment clean and well ventilated and provide good quality food. To diagnose the problem your best move would be to consult a vet with any of the sick ones to check for diseases because if you don't you may start losing birds. Generally birds dont show signs of illness until they are really sick.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]