Individual study: Supplementary food can increase great tit Parus major nestling size, weight and colouration, but does not increase fledging success in polluted and unpolluted sites in Finland
Eeva T., Sillanpaa S. & Salminen J.P. (2009) The effects of diet quality and quantity on plumage colour and growth of great tit Parus major nestlings: a food manipulation experiment along a pollution gradient. Journal of Avian Biology, 40, 491-499
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Provide supplementary food for songbirds to increase reproductive success
A replicated and controlled study in open pine Pinus sylvestris forests in southwest Finland in 2005 (Eeva et al. 2009) provided 87 great tit Parus major nestlings with three supplementary diets: autumnal moth Epirrita autumnata larvae (high in carotenoids – chemicals needed for coloured feathers) and mealworms (diet 1); mealworms and water-dispersed lutein (an important carotenoid, diet 2); mealworms and distilled water (diet 3). Nestlings fed on diets 1 and 2 were larger and heavier than control (unfed) nestlings and nestlings fed on diet 3, but only in areas with high levels of heavy metal pollution (polluted areas: average wing length of approximately 46 mm and body mass of 16.5 g for diet 1 nestlings vs. 46 mm and 15.8 g for diet 2 vs. 44 mm and 15.0 g for diet 3 and 43 mm and 15.0 g for controls; unpolluted areas: 48 mm and 16.5 g for diet 1 vs. 46 mm and 16 g for diet 2 vs. 46 mm and 16.5 g for diet 3 vs. 47 mm and 17 g for controls). In addition, diet 2 nestlings had higher blood lutein levels and correspondingly higher carotenoid chroma (a measure of colour intensity) in breast feathers than other diets and control chicks across both pollution levels (7.5-15.0 µg/ml blood lutein and 0.30-0.35 carotenoid chroma for diet 1 vs. 24.0-28.0 µg/ml and 0.41-0.45 for diet 2 vs. 7.5-16.0 µg/ml and 0.30-0.36 for diet 3 vs. 5.5-17.5 µg/ml and 0.30-0.36 for controls). Supplementary food did not have an effect on fledgling probability. One gram of food was provided every other day from the third day after hatching to the 13th, making approximately 20% of the required food in this time.