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Mites on birds
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References 1 Proctor, H. and Owens, I. (2000) Mites and birds: diversity, parasitism and coevolution. Trends Ecol. Evol. 15, 358–364 2 Verbeek, N.A.M. and Morgan, J.L. (1980) Removal of primary remiges and its effect on the flying ability of glaucous-winged gulls. Condor 82, 224–226 3 Davidson, W.R. et al. (1989) Feather damage due to mycotic infections in wild turkeys. J. Wildl. Dis. 25, 534–539 4 Burtt, E.H. and Ichida, J.M. (1999) Occurrence of feather-degrading bacilli in the plumage of birds. Auk 116, 364–372 5 Bonser, R.H.C. (1996) The mechanical properties of feather keratin. J. Zool. London 239, 477–484 6 Purslow, P.P. and Vincent, J.F.V. (1978) Mechanical properties of primary feathers from the pigeon. J. Exp. Biol. 72, 251–260 7 Crenshaw, D.G. (1980) Design and materials of feather shafts: very light, rigid structures. Symp. Soc. Exp. Biol. 34, 485–486 8 Kose, M. and Møller, A.P. (1999) Sexual selection, feather breakage and parasites: the importance of white spots in the tail of the barn swallow (Hirundo rustica). Behav. Ecol. Sociobiol. 45, 430–436 9 Hillerton, J.E. et al. (1982) On the indentation hardness of insect cuticle. J. Exp. Biol. 96, 45–52 10 Bonser, R.H.C. (1995) Melanin and the abrasion resistance of feathers. Condor 97, 590–591 11 Choe, J.C. and Kim, K.C. (1991) Microhabitat selection and adaptation of feather mites (Acari: Analgoidea) on murres and kittiwakes. Can. J. Zool. 69, 817–821 12 Müller, W. and Patone, G. (1998) Air transmissivity of feathers. J. Exp. Biol. 201, 2591–2599 13 Ennos, A.R. et al. (1995) Functional morphology of the vanes of the flight feathers of the pigeon Columba livia. J. Exp. Biol. 198, 1219–1228 PII: S0169-5347(00)02012-7
Mites on birds Comment from Harper & Randall
Proctor and Owens’ TREE review1 of the mites associated with birds will encourage improvement in research design. However, we have reservations about one of their suggestions for studying feather mites: ‘[p]lucking a few feathers from the wings will provide a fair estimate of incidence and will allow identification of mite taxa’. This claim is only partially true and the method has serious drawbacks. We agree that plucking feathers allows observers to count mites more reliably and reproducibly than if feathers are left in situ1,2, and that these mites remain available for identification3 or behavioural studies4. Neither advantage is unique, however, to feathers plucked from live birds because feathers from freshly dead birds (e.g. road accidents, predator kills) provide similar material. Moreover, data from a few feathers could be seriously misleading with respect to mite incidence
TRENDS in Ecology & Evolution Vol.16 No.1 January 2001
and species composition, both of which can vary dramatically across the wing2,4. The usual method of estimating feather mite load is an index based on visual inspection of the flight feathers of one ‘wing held to light’ (or against a bright background)2,4–7. Using this method, most of the diurnal variation in apparent mite load4 occurs when mites move between the feather shaft (rachis) and exposed vane5. This ought not to cause problems so long as observers are aware of the possibility of this movement, and use a magnifier lamp when necessary. Movements of mites between the flight feathers and other plumage tracts4,5 will make any estimate of mite load imprecise unless the entire plumage is sampled. We conclude that plucking feathers usually offers little advantage over a combination of examining dead birds in detail and obtaining a crude index quickly from live birds using the ‘wing held to light’ method. This method is, however, difficult to apply to some of the wildfowl (Anseriformes), raptors (Accipitriformes) and gamebirds (Galliformes) because mites can be hidden by ventral extensions on the barbs of the flight feathers4,8. The main scientific drawback to plucking feathers is that it alters the host’s mite load, preventing the longitudinal studies of individual hosts5–7 that are required to answer many of the outstanding questions about feather mites1. More important is the ethical problem: removing flight feathers seriously harms birds9,10 and is illegal in many countries, including the UK. Everyone inspired to study feather mites by Proctor and Owens’ review1 should think before they pluck. David G.C. Harper* David P. Randall School of Biological Sciences, University of Sussex, Falmer, Brighton, UK BN1 9QG. *e-mail: [email protected] References 1 Proctor, H. and Owens, I. (2000) Mites and birds: diversity, parasitism and coevolution. Trends Ecol. Evol. 15, 358–364 2 Behnke, J. et al. (1999) Semi-quantitative assessment of wing feather mite (Acarina) infestations on passerine birds from Portugal: evaluation of the criteria for accurate quantification of mite burdens. J. Zool. 248, 337–347 3 Gaud, J. and Atyeo, T. (1996) Feather Mites of the World, Musee Royal de l’Afrique Centrale 4 Dubunin, V.B. (1951) Feather mites (Analgesoidea). Part I. Introduction to their study. Fauna USSR 6, 1–363
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5 McClure, H.E. (1989) Occurrence of feather mites (Proctophyllodidae) among birds of Ventura County lowlands, California. J. Field Ornithol. 60, 431–450 6 Thompson, C.W. et al. (1997) High parasite load in house finches (Carpodacus mexicanus) is correlated with reduced expression of a sexually selected trait. Am. Nat. 149, 270–294 7 Harper, D.G.C. (1999) Feather mites (Acari, Proctophyllodidae), pectoral muscle condition, wing length and plumage coloration of passerines. Anim. Behav. 58, 553–562 8 Peterson, P.C. (1975) An analysis of host-parasite associations among feather mites (Acari: Analgoidea). Misc. Publ. Entomol. Soc. Am.9, 237–242 9 Møller, A.P. et al. (1995) Morphological adaptations to an extreme sexual display, stone-carrying in the black wheatear, Oenanthe leucura. Behav. Ecol. 6, 368–375 10 Moreno, J. et al. (1999) Maternal energy expenditure does not change with flight costs or food availability in the pied flycatcher (Ficedula hypoleuca): costs and benefits for nestlings. Behav. Ecol. Sociobiol. 46, 244–251 PII: S0169-5347(00)02014-0
Mites on birds Response from Proctor & Owens
Both sets of correspondents1,2 focus on feather mites. Although we agree with many of the issues that the authors raise, some aspects merit further comment. Bonser1 raises two points: (1) medullaeating mites might weaken the feather; and (2) ‘feather-chewing mites’ might lead to poor flight performance. We agree with Bonser’s first point. His measures of the importance of the medulla and of the negative effects that medulla-feeding mites might have on the structural integrity of feathers are fascinating and support the conjecture we made in our recent TREE review3. However, we disagree with Bonser’s second point. He suggests that plumicolous feather mites – those living on the outside of the feather – chew holes in feathers and might feed preferentially on unmelanized areas. Unfortunately, it seems that Bonser has misread the report by Kose and Møller4, which deals with feather lice (insects) rather than feather mites (arachnids). As we discussed in our original article3, the vast majority of plumicolous feather mites feed on feather oils and the pollen and fungi that accumulate in these oils, not on the keratin of the feathers themselves. The best known exceptions are mites that live in the plumage of herons and bitterns (Ardeidae) and feed on powder down5 – material that has a grooming, rather than a structural, function6. To our knowledge,
http://tree.trends.com 0169–5347/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
References 1 Proctor, H. and Owens, I. (2000) Mites and birds: diversity, parasitism and coevolution. Trends Ecol. Evol. 15, 358–364 2 Verbeek, N.A.M. and Morgan, J.L. (1980) Removal of primary remiges and its effect on the flying ability of glaucous-winged gulls. Condor 82, 224–226 3 Davidson, W.R. et al. (1989) Feather damage due to mycotic infections in wild turkeys. J. Wildl. Dis. 25, 534–539 4 Burtt, E.H. and Ichida, J.M. (1999) Occurrence of feather-degrading bacilli in the plumage of birds. Auk 116, 364–372 5 Bonser, R.H.C. (1996) The mechanical properties of feather keratin. J. Zool. London 239, 477–484 6 Purslow, P.P. and Vincent, J.F.V. (1978) Mechanical properties of primary feathers from the pigeon. J. Exp. Biol. 72, 251–260 7 Crenshaw, D.G. (1980) Design and materials of feather shafts: very light, rigid structures. Symp. Soc. Exp. Biol. 34, 485–486 8 Kose, M. and Møller, A.P. (1999) Sexual selection, feather breakage and parasites: the importance of white spots in the tail of the barn swallow (Hirundo rustica). Behav. Ecol. Sociobiol. 45, 430–436 9 Hillerton, J.E. et al. (1982) On the indentation hardness of insect cuticle. J. Exp. Biol. 96, 45–52 10 Bonser, R.H.C. (1995) Melanin and the abrasion resistance of feathers. Condor 97, 590–591 11 Choe, J.C. and Kim, K.C. (1991) Microhabitat selection and adaptation of feather mites (Acari: Analgoidea) on murres and kittiwakes. Can. J. Zool. 69, 817–821 12 Müller, W. and Patone, G. (1998) Air transmissivity of feathers. J. Exp. Biol. 201, 2591–2599 13 Ennos, A.R. et al. (1995) Functional morphology of the vanes of the flight feathers of the pigeon Columba livia. J. Exp. Biol. 198, 1219–1228 PII: S0169-5347(00)02012-7
Mites on birds Comment from Harper & Randall
Proctor and Owens’ TREE review1 of the mites associated with birds will encourage improvement in research design. However, we have reservations about one of their suggestions for studying feather mites: ‘[p]lucking a few feathers from the wings will provide a fair estimate of incidence and will allow identification of mite taxa’. This claim is only partially true and the method has serious drawbacks. We agree that plucking feathers allows observers to count mites more reliably and reproducibly than if feathers are left in situ1,2, and that these mites remain available for identification3 or behavioural studies4. Neither advantage is unique, however, to feathers plucked from live birds because feathers from freshly dead birds (e.g. road accidents, predator kills) provide similar material. Moreover, data from a few feathers could be seriously misleading with respect to mite incidence
TRENDS in Ecology & Evolution Vol.16 No.1 January 2001
and species composition, both of which can vary dramatically across the wing2,4. The usual method of estimating feather mite load is an index based on visual inspection of the flight feathers of one ‘wing held to light’ (or against a bright background)2,4–7. Using this method, most of the diurnal variation in apparent mite load4 occurs when mites move between the feather shaft (rachis) and exposed vane5. This ought not to cause problems so long as observers are aware of the possibility of this movement, and use a magnifier lamp when necessary. Movements of mites between the flight feathers and other plumage tracts4,5 will make any estimate of mite load imprecise unless the entire plumage is sampled. We conclude that plucking feathers usually offers little advantage over a combination of examining dead birds in detail and obtaining a crude index quickly from live birds using the ‘wing held to light’ method. This method is, however, difficult to apply to some of the wildfowl (Anseriformes), raptors (Accipitriformes) and gamebirds (Galliformes) because mites can be hidden by ventral extensions on the barbs of the flight feathers4,8. The main scientific drawback to plucking feathers is that it alters the host’s mite load, preventing the longitudinal studies of individual hosts5–7 that are required to answer many of the outstanding questions about feather mites1. More important is the ethical problem: removing flight feathers seriously harms birds9,10 and is illegal in many countries, including the UK. Everyone inspired to study feather mites by Proctor and Owens’ review1 should think before they pluck. David G.C. Harper* David P. Randall School of Biological Sciences, University of Sussex, Falmer, Brighton, UK BN1 9QG. *e-mail: [email protected] References 1 Proctor, H. and Owens, I. (2000) Mites and birds: diversity, parasitism and coevolution. Trends Ecol. Evol. 15, 358–364 2 Behnke, J. et al. (1999) Semi-quantitative assessment of wing feather mite (Acarina) infestations on passerine birds from Portugal: evaluation of the criteria for accurate quantification of mite burdens. J. Zool. 248, 337–347 3 Gaud, J. and Atyeo, T. (1996) Feather Mites of the World, Musee Royal de l’Afrique Centrale 4 Dubunin, V.B. (1951) Feather mites (Analgesoidea). Part I. Introduction to their study. Fauna USSR 6, 1–363
19
5 McClure, H.E. (1989) Occurrence of feather mites (Proctophyllodidae) among birds of Ventura County lowlands, California. J. Field Ornithol. 60, 431–450 6 Thompson, C.W. et al. (1997) High parasite load in house finches (Carpodacus mexicanus) is correlated with reduced expression of a sexually selected trait. Am. Nat. 149, 270–294 7 Harper, D.G.C. (1999) Feather mites (Acari, Proctophyllodidae), pectoral muscle condition, wing length and plumage coloration of passerines. Anim. Behav. 58, 553–562 8 Peterson, P.C. (1975) An analysis of host-parasite associations among feather mites (Acari: Analgoidea). Misc. Publ. Entomol. Soc. Am.9, 237–242 9 Møller, A.P. et al. (1995) Morphological adaptations to an extreme sexual display, stone-carrying in the black wheatear, Oenanthe leucura. Behav. Ecol. 6, 368–375 10 Moreno, J. et al. (1999) Maternal energy expenditure does not change with flight costs or food availability in the pied flycatcher (Ficedula hypoleuca): costs and benefits for nestlings. Behav. Ecol. Sociobiol. 46, 244–251 PII: S0169-5347(00)02014-0
Mites on birds Response from Proctor & Owens
Both sets of correspondents1,2 focus on feather mites. Although we agree with many of the issues that the authors raise, some aspects merit further comment. Bonser1 raises two points: (1) medullaeating mites might weaken the feather; and (2) ‘feather-chewing mites’ might lead to poor flight performance. We agree with Bonser’s first point. His measures of the importance of the medulla and of the negative effects that medulla-feeding mites might have on the structural integrity of feathers are fascinating and support the conjecture we made in our recent TREE review3. However, we disagree with Bonser’s second point. He suggests that plumicolous feather mites – those living on the outside of the feather – chew holes in feathers and might feed preferentially on unmelanized areas. Unfortunately, it seems that Bonser has misread the report by Kose and Møller4, which deals with feather lice (insects) rather than feather mites (arachnids). As we discussed in our original article3, the vast majority of plumicolous feather mites feed on feather oils and the pollen and fungi that accumulate in these oils, not on the keratin of the feathers themselves. The best known exceptions are mites that live in the plumage of herons and bitterns (Ardeidae) and feed on powder down5 – material that has a grooming, rather than a structural, function6. To our knowledge,
http://tree.trends.com 0169–5347/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.