Detecting Omnivory with Δ Δ 15 N

is no unambiguous evidence that plumicolous feather mites chew holes in feathers; such damage is usually caused by feather lice. Also, it has been reported that feather mites of the great-spotted woodpecker (Dryobates major) and the hoopoe (Upupa epops) avoid white spots on the feathers and instead aggregate on melanized areas 5. Thus, as we stressed in our review 3 , extrapolating from lice to mites is not always straightforward. Harper and Randall 2 provide a critique of the pros and cons of feather plucking. They argue that a combination of examining mites on dead birds and rough counts of mites on the wings of live birds is a superior method because feather plucking: (1) is illegal in many countries; (2) might hinder flight performance; (3) gives a less-than-perfect estimate of overall mite abundance; and (4) interferes with longitudinal studies of mite–bird interactions. Although we agree that ornithologists should be critical about their mite-counting techniques, we do not think that feather plucking (or cutting) should be rejected. With respect to criticisms (1) and (2), the legal and moral difficulties described are not unique to this method and should be dealt with by weighing scientific merit against probable harm. To our knowledge, feather plucking and/or cutting has been employed in Europe, Asia, North America and Australasia to study feather development 7 , flight performance 8 , energetics 9 , environmental pollution 10 , sexual selection 11 and genetics 12. Similarly, criticisms (3) and (4) are true of many methods and can be dealt with by conventional control treatments 4,8,9,11. Finally, we would like to urge caution regarding the examination of dead birds alone to study mite–bird interactions. Although mite specimens and some qualitative information can be gained from corpses, it would be a bold ornithologist who assumed the numbers and identities of mites on dead birds reliably reflected those found on healthy individuals. The contribution of insulation changes to the energy cost of avian moult. Can. Feathers as a means of monitoring mercury in seabirds: insights from stable isotope analysis. Experimental analysis of sexual and natural selection on short tails in a polygynous warbler. A single plucked feather as a source of DNA for bird genetic studies. In a recent TREE review, Eggers and Jones 1 suggest that recently published isotopic data 2,3 provide 'evidence that omnivory is common in soil food webs'. Being the authors of one of these studies …