Semi-quantitative assessment of wing feather mite (Acarina) infestations on passerine birds from Portugal. Evaluation of the criteria for accurate quantification of mite burdens

Abstract

Wing feather mite burdens on seven species of passerine birds (Carduelis carduelis – goldfinch; C. chloris – greenfinch; Serinus serinus – serin; Sylvia atricapilla – blackcap; Sylvia melanocephala – Sardinian warbler; Turdus merula – blackbird; Passer domesticus – house sparrow) from Portugal were assessed by the subjective semi-quantitative scoring system of Behnke et al. (1995) in order to evaluate more fully the accuracy and reliability of the technique. Our analysis indicated that in all species, scores allocated to flight feathers showed a significant positive relationship with mite counts as assessed through microscopical examination of the same feathers. However, there were differences between species of birds. Of the species examined, goldfinches and greenfinches showed the weakest relationships between assigned mite scores and actual mite numbers indicating that the technique was less accurate when applied to these species compared with the remaining five. No evidence was found that anything more was to be gained from scoring both wings, rather than just one. Feather mites (Proctophyllodes spp., Trouessartia incisa) were also detected on tail feathers, but the assessment of these feathers presented additional problems and it was concluded that in the interests of minimizing handling time of birds, tail scores had little more to offer. We conclude that scoring all the flight feathers (including all primary, secondary, and tertiary feathers) on one entire wing, but alternating between left and right wings of birds within a species, represents an acceptable compromise between sufficiently detailed examination and minimization of bird handling time in the field.