Simplifying the phytohaemagglutinin skin-testing technique in studies of avian immunocompetence

1. Researchers involved in ecology and toxicology, as well as many other aspects of avian biology, use phytohaemagglutinin (PHA) skin testing as a means of evaluating the immune status of individuals.
2. Immune function, one measure of individual quality, can be used as a sensitive, non-lethal variable that may be negatively affected in animals exposed to degraded, contaminated or otherwise disturbed ecological zones.
3. Typically this test has been applied by challenging one wing web with the immunostimulant PHA, while the other 'control' wing is injected with phosphate buffered saline (PBS). Injection sites on the wing web are measured before and 24 h after injection with PHA or PBS. The immune response is considered to be the difference between the two wings.
4. Results from PHA skin tests conducted on 608 birds in seven studies representing passerines, waterfowl, upland game birds and raptors are examined.
5. Numerous advantages to eliminating the PBS injection as the experimental control are: (i) decrease by half, the time required for testing; (ii) decrease handling-related stress on the birds (proportional to handling time); (iii) reduce the probability of errors at injection time; (iv) spare the other wing for different tests or uses (e.g. tuberculin DTH testing); and (v) decrease the coefficient of variation that is due to measurement inaccuracies.
6. The only disadvantage identified is that hypersensitive individuals (outliers) could be missed, which in this case represents 2 of 608 individuals.