Feather hole

File:Feather hole.jpg lice on the tail feather of Barn swallow.]]

Feather holes often characteristically occur on wing and tail feathers of some small-bodied species of passerines. In the case of barn swallows, it was suggested that the holes were feeding traces of avian lice, either Machaerilaemus malleus and/or Myrsidea rustica (both Phthiraptera: Amblycera).{{cite book|last=Møller|first=A. P.|year=1991|title=Parasites, sexual ornaments and mate choice in the Barn Swallow Hirundo rustica. In: Loye, J. E.; Zuk, M (eds) Bird-parasite interactions: Ecology, evolution, and behaviour|publisher=Oxford University Press| pages= 328–343}}

Hole counts were shown to be highly repeatable, and thus counts appeared to be useful measures to quantify the intensity of infestation. Since then, a number of influential papers have been published on the evolutionary, ecological, and behavioral aspects of host-parasite interactions based on the assumption that holes were chewed by Machaerilaemus malleus. More specifically, host sexual selection,{{cite journal | last= Kose| first= M. |author2=Mand, R. |author3=Møller, A. P.| s2cid= 24583746 | year= 1999| title= Sexual selection for white tail spots in the barn swallow in relation to habitat choice by feather lice | journal= Animal Behaviour | volume= 58| issue= 6 | pages= 1201–1205 | doi=10.1006/anbe.1999.1249 | pmid=10600140}} feather breakage,{{cite journal | last= Kose| first= M.|author2=Møller, A. P.| year= 1999| title= Sexual selection, feather breakage and parasites: the importance of white spots in the tail of the barn swallow (Hirundo rustica) | journal= Behavioral Ecology and Sociobiology | volume= 45| issue= 6| pages= 430–436 | doi=10.1007/s002650050581| bibcode= 1999BEcoS..45..430K| s2cid= 22196756}} flight performance,{{cite journal | last= Barbosa| first= A |author2=Merino, S. |author3=de Lope, F. |author4=Møller, A.P. | year= 2002| title= Effects of feather lice on flight behavior of male Barn Swallows (Hirundo rustica)| journal= The Auk | volume= 119| issue= 1 | pages= 213–216 | doi=10.2307/4090025| jstor= 4090025 | doi-access= free }} immunity levels,{{cite journal | last= Møller| first= A. P. |author2=de Lope, F |author3=Saino, N.| year= 2004| title= Parasitism, immunity, and arrival date in a migratory bird, the Barn Swallow | journal= Ecology | volume= 85| issue= 1 | pages= 206–219 | doi=10.1890/02-0451| bibcode= 2004Ecol...85..206M | doi-access= free}} arrival dates,{{cite journal| last= Pap| first= P. L.| author2= Tökölyi, J.| author3= Szép, T.| year= 2005| title= Frequency and consequences of feather holes in barn swallows Hirundo rustica| journal= Ibis| volume= 147| pages= 169–175| doi= 10.1111/j.1474-919x.2004.00386.x| doi-access= free}} and even song characteristics{{cite journal | last1= Garamszegi| first1= L. Z.|last2=Heylen |first2=D. |last3=Møller |first3=A. P. |last4=Eens |first4=M. |last5=de Lope |first5=F. | year= 2005| title= Age dependent health status and song characteristics in the barn swallow | journal= Behavioral Ecology | volume= 16| issue= 3| pages= 580–591 | doi=10.1093/beheco/ari029| doi-access=free }} were shown to covary with the number of holes. Cross-fostering experiments showed that infestation levels were heritable.{{cite journal | last= Møller| first= A. P. |author2=Martinelli, R. |author3=Saino, N.| year= 2004| title= Genetic variation in infestation with a directly transmitted ectoparasite | journal= Journal of Evolutionary Biology | volume= 17| issue= 1 | pages= 41–47 | doi=10.1046/j.1420-9101.2003.00660.x| pmid= 15000646 | doi-access= free }}

Recently, however, it was shown that Machaerilaemus malleus is apparently absent from Europe, where all these studies were carried out. Correlational evidence supports the hypothesis that feather holes are feeding traces of lice, however, the occurrence of Brueelia spp. lice (Phthiraptera: Ischnocera) provides the best fit to the distribution and abundance of feather holes both in barn swallows and across several small passerines.{{cite journal | last= Vas| first= Z. |author2=Csörgő, T. |author3=Møller, A. P |author4=Rózsa, L. | year= 2008| url= http://www.zoologia.hu/list/Vas_et_al.pdf |title=The feather holes on the barn swallow Hirundo rustica and other small passerines are probably caused by Brueelia spp. lice | journal= Journal of Parasitology | volume= 94| issue= 6 | pages= 1438–1440 | doi=10.1645/GE-1542.1 | pmid=18576840| s2cid= 6713948 }}