1 3 Oecologia DOI 10.1007/s00442-015-3238-1 PLANT-MICROBE-ANIMAL INTERACTIONS - ORIGINAL RESEARCH Manipulation of parental effort affects plumage bacterial load in a wild passerine Grete Alt · Pauli Saag · Marko Mägi · Veljo Kisand · Raivo Mänd Received: 13 February 2014 / Accepted: 14 January 2015 © Springer-Verlag Berlin Heidelberg 2015 Keywords Microbe–host · Microbiota · Parental care · Brood size · Preening Introduction Avian plumage is a diverse ecosystem that harbors a com- plex community of ectoparasites and microorganisms (Clayton and Moore 1997; Clayton 1999; Hubàlek 2004). While plumage invertebrates, especially mites, are rela- tively well studied (Dabert and Mironov 1999; Proctor and Owens 2000; Blanco et al. 2001; Møller et al. 2010; Rubt- sov and Yakimenko 2012), the study of plumage microbiota has only recently come into focus, with the majority of such studies concentrating solely on feather-degrading bacteria (Gunderson 2008; Burtt 2009). Nonetheless, microorgan- isms are expected to play an important role in shaping the life history traits and behavior of their avian hosts (Clay- ton and Moore 1997; Burtt and Ichida 1999; Muza et al. 2000; Gunderson et al. 2009; Peele et al. 2009; Archie and Theis 2011; Møller et al. 2012; Sorci 2013). Consequently, the relationship between wild birds and microorganisms is increasingly becoming a focus of ecological research (e.g., Burtt 2009; Goodenough and Stallwood 2010; Saag et al. 2011a, 2012; Kilgas et al. 2012; Giraudeau et al. 2013; Romano et al. 2014; Sorci 2013; Czirják et al. 2013; Møller et al. 2013). Plumage microorganisms interact with birds in different ways. Certain bacteria are capable of degrading β-keratin, a protein that constitutes more than 90 % of feather mass (Burtt and Ichida 1999; Sangali and Brandelli 2000; Lucas et al. 2003b). Damaged plumage may be costly in terms of thermal insulation (Brush 1965; Stettenheim 2000; Ichida et al. 2001) and flight efficiency (Swaddle et al. 1996; Møller et al. 2012). Several authors have also suggested Abstract It has been suggested that plumage microorgan- isms play an important role in shaping the life histories of wild birds. Some bacteria may act as pathogens or cause damage to feathers, and thereby reduce individual fitness. Intense parental care in birds can result in a reduction of self-maintenance and preening behavior in parents and therefore might affect the dynamics of microbiota living on their feathers. However, experimental evidence of this relationship is virtually absent. We manipulated the paren- tal effort of wild breeding pied flycatcher (Ficedula hypole- uca) females by modifying their brood size or temporarily removing male partners. We expected that experimentally decreasing or increasing parental effort would affect feather sanitation in females and therefore also bacterial density on their plumage. In accordance with this hypothesis, manipu- lation affected the density of free-living bacteria: females with reduced broods had the lowest number of free-living bacteria on their feathers, while females left without male partners had the highest. However, manipulation did not have a significant effect on the densities of attached bacte- ria. Our results provide experimental evidence that a trade- off between self-maintenance and parental effort affects plumage bacterial densities in birds. Communicated by Oliver P. Love. G. Alt (*) · P. Saag · M. Mägi · R. Mänd Department of Zoology, Institute of Ecology and Earth Sciences, University of Tartu, 46 Vanemuise Str., 51014 Tartu, Estonia e-mail: grt@ut.ee V. Kisand Institute of Technology, University of Tartu, 1 Nooruse Str., 50411 Tartu, Estonia