title: Social cues are unlikely to be the single cause for early reproduction in urban European blackbirds (Turdus merula).
abstract: Despite urban ecology being an established field of research, there is still surprisingly little information about the relative contribution of specific environmental factors driving the observed changes in the behavior and physiology of city dwellers. One of the most reported effects of urbanization is the advanced phenology observed in birds. Many factors have been suggested to underline such effect, including warmer microclimate, anthropogenic food supply and light pollution. Since social stimuli are known to affect reproductive timing and breeding density is usually higher in urban populations compared to rural ones, we experimentally tested whether social interactions could advance the onset of reproduction in European blackbirds (Turdus merula). We housed male blackbirds of rural and urban origins with or without a conspecific female, and recorded their seasonal variation in gonadal size and production of luteinizing hormone (LH). Paired and unpaired males of both urban and rural origins did not significantly differ in their timing of gonadal growth. Moreover, rural and urban birds did not differ in their response to the social stimuli, rather they became reproductively active at the same time, a result that confirms previous studies that attributed the difference in reproductive timing observed in the field to phenotypic plasticity. We conclude that social stimuli do not contribute substantially to the observed early onset of reproductive physiology in urban bird species, rather other factors such as light pollution are likely to be stronger drivers of these physiological changes.
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G128QQ, UK; Department of Migration and Immuno-ecology, Max Planck Institute for Ornithology, 78315 Radolfzell, Germany; Department of Biology, University of Konstanz, 78457 Konstanz, Germany. Electronic address: davide.dominoni@glasgow.ac.uk.
authors.forename: Davide M
authors.initials: DM
authors.lastname: Dominoni
authors.affiliation: Takizaki Corporation, 2-4-7 Honkomagome, Bunkyo-ku, Tokyo 113-0021, Japan.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Van't Hof
authors.affiliation: Department of Migration and Immuno-ecology, Max Planck Institute for Ornithology, 78315 Radolfzell, Germany; Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
authors.forename: Jesko
authors.initials: J
authors.lastname: Partecke
mesh_terms: D000818:Animals; D002947:Cities; D003463:Cues; D004777:Environment; D005260:Female; D065928:Forests; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009929:Organ Size; D046109:Passeriformes / Q000033:anatomy & histology / Q000502:physiology*; D017440:Photoperiod; D012098:Reproduction / Q000502:physiology*; D012919:Social Behavior; D013737:Testis / Q000033:anatomy & histology / Q000502:physiology; D013997:Time Factors
chemical_list: D007986:Luteinizing Hormone
keywords: Light at night; Light pollution; Social cues; Social stimuli; Timing of reproduction; Urbanization