The bird fleas of Fair Isle

Abstract

Approximately 5000 birds (78 species) were trapped on Fair Isle and examined for fleas. Six species of flea were recorded: D. g. gallinulae (430 records), C. gallinae (205 records), C. borealis (126 records), C. garei (4 records), C. fringillae and C. vagabundus (1 record each).The infestation rate among spring-passage migrants was 52·2% and among autumn-passage migrants only 2·7%. Spring migrants released and retrapped after ‘de-fleaing’ in the Fair Isle apparatus showed a 55% re-infestation rate. On spring migrants D. g. gallinulae was the dominant flea, but on autumn migrants C. gallinae was dominant. The most heavily infested group of birds were the Turdidae (61% spring, 3% autumn infestation rate) and Sylviidae (53% spring, 1% autumn infestation rate).A number of double and triple infestations with 2 or 3 species of flea is recorded. Double infestations involving D. g. gallinulae and C. borealis occur more frequently than would be expected for purely chance associations. More male birds (90) than female birds (70) were infested.The sex ratio of the fleas (on the bodies of birds) was: D. g. gallinulae 294 males, 325 females; C. gallinae 115 males, 214 females; C. borealis 77 males, 77 females. On the spring migrants there was an excess of male D. g. gallinulae and on the autumn migrants an excess of females.On the resident birds there was definite evidence of host preference. The starling was the chief host of C. gallinae, the pipits of D. g. gallinulae and the wheatear of C. borealis. The re-infestation rate of ‘de-fleaed’ retraps showed a higher rate than original trappings in all cases, but the lack of D. g. gallinulae on retrapped starlings suggested some host selection on the part of the flea.The proportions of the three principal species of flea found in (i) the nest of the wheatear, and (ii) on the body of the bird were strikingly different.