title: Metal pollution does not bias offspring sex ratio in great tit (Parus major).
abstract: OBJECTIVE
  We measured offspring sex ratios in a resident insectivorous passerine bird, the Great tit Parus major, to find out whether metal pollution around a Finnish copper smelter would bias sex ratios in this territorial forest bird species. Besides a direct effect of pollutants, we were interested in possible indirect effects of pollution-related resource limitation, i.e., changes in food quality and quantity, on sex ratio.
  
  
  METHODS
  We manipulated the diet quantity and quality (carotenoid levels) of P. major nestlings in polluted and unpolluted environments to find out if variation in dietary resource levels has any effect on fledgling sex ratios. Faecal metal levels of nestlings were analysed to monitor the level of pollution exposure at each territory. Near the time of fledging (at the age of 15 days), feather samples were collected for molecular sex determination.
  
  
  RESULTS
  We did not find any association between metal exposure levels and offspring sex ratio, and thus, our results do not support the hypothesis that metal pollution would have direct effects on P. major offspring sex ratio. We found that, irrespective of pollution level, high nestling mortality was associated with male-biased sex ratio, most likely due to sex-specific mortality. Our feeding treatment, however, showed no significant effects on offspring sex ratio, possibly because natural variation in food availability outweighed the effect of our food manipulation on nestling mortality.
  
  
  CONCLUSIONS
  We conclude that metal exposure at the levels found in our study area does not bias fledgling sex ratios in this species, but biased sex ratios may follow under natural or pollution-related resource limitation.
authors.affiliation: Section of Ecology, Department of Biology, University of Turku, 20014, Turku, Finland. tapio.eeva@utu.fi
authors.forename: Tapio
authors.initials: T
authors.lastname: Eeva
authors.forename: Saila
authors.initials: S
authors.lastname: Sillanpää
authors.forename: Esa
authors.initials: E
authors.lastname: Lehikoinen
mesh_terms: D000818:Animals; D001835:Body Weight; D003300:Copper / Q000737:chemistry / Q000633:toxicity*; D017753:Ecosystem; D004781:Environmental Exposure; D004784:Environmental Monitoring / Q000379:methods*; D004785:Environmental Pollutants / Q000737:chemistry / Q000633:toxicity*; D005260:Female; D005387:Finland; D008297:Male; D008669:Metallurgy; D008670:Metals / Q000737:chemistry / Q000633:toxicity*; D046109:Passeriformes / Q000502:physiology*; D012744:Sex Ratio
chemical_list: D004785:Environmental Pollutants; D008670:Metals; D003300:Copper