Negro J.J., Bildstein K.L. & Bird D.M. (1994) Effects of food deprivation and handling stress on fault-bar formation in nestling American kestrels: Falco sparverius. ARDEA 82 (2): 263-267

We document the extent of fault-bar formation in the wing and tail feathers of 45 hand-reared and 18 parentally reared American Kestrels Falco sparverius raised in captivity on temporarily interrupted (30 birds) and uninterrupted (15 birds) ad libitum diets. Hand-reared birds were handled extensively throughout the experiment, parentally reared birds were not. Hand-reared nestlings developed an average of 2.8, 8.0 and 4.3 and parentally reared nestlings an average of 0.6, 1.4 and 0.4 fault bars on their rectrices, primaries and secondaries, respectively. All hand-reared birds, including the group whose diet was not interrupted, had significantly more fault bars on their rectrices, primaries and secondaries, than did parentally reared birds. Fault-bar formation in birds whose ad libitum diets were interrupted did not increase at times of food deprivation and handreared birds from which ad libitum food had been withheld for 24 to 48 hours did not have more fault bars than hand-reared birds whose diets had not been interrupted. Our results suggest that excessive fault-bar formation in captive birds is most likely due to handling stress, rather than to food deprivation.