Individual study: Supplementary feeding appears to increase reproductive success but reduce adult survival in song sparrows Melospiza melodia on an island in British Colombia
Arcese P. & Smith J.N.M. (1988) Effects of population density and supplemental food on reproduction in song sparrows. Journal of Animal Ecology, 57, 119-136
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Provide supplementary food for songbirds to increase adult survival
A replicated and controlled study on Mandarte Island, British Colombia, Canada (Arcese & Smith 1988), found that song sparrows Melospiza melodia provided with supplementary food in 1985 were less likely to survive until the breeding season of 1986 (40-47% survival for fed adults, n = 15 vs. 66-79% for controls, n = 42). The authors note that 1985 was a year of peak song sparrow density and suggest lower adult survival could be due to increased costs of defending feeders from other song sparrows. This study also described the impact of feeding on reproduction, discussed in ‘Provide supplementary food to increase reproductive success’.
Provide supplementary food for songbirds to increase reproductive success
A replicated and controlled study on Mandarte Island, British Colombia, Canada (Arcese & Smith 1988), found that song sparrows Melospiza melodia provided with supplementary food in 1985 laid earlier, had larger clutches than control (unfed) birds, were more likely to re-nest following breeding failures and were less likely to be parasitized by brown-headed cowbirds Molothrus ater (average laying date of 10th April, 3.3 eggs/clutch, 2.8 breeding attempts and 18% of nests parasitized for 15 fed pairs vs. 28th April, 2.8 eggs/clutch, 2.2 breeding attempts and 45% for 34 controls). This led to fed females raising approximately 3.8 young/female to independence compared to 1.0 young/female for controls. However, eggs and nestlings from fed birds were no larger than those from controls nor more likely to hatch or survive to independence (averages of 3.1 g/egg, 16.8 g/nestling at six days old, 78% hatching success and 83% survival to independence vs. 3.0 g/egg, 15.6g, 73% and 70%) and young from fed territories did not have enhanced reproduction (8.6% of 58 fed young reproducing vs. 12.5% for 40 controls). Supplementary food consisted of dog food, vitamins, mealworms Tenerbrio sp. and millet seed provided continuously in feeders in the centre of each territory from five weeks before laying started (28th February) until the last young had left the nest (24th July). The authors note that 1985 was a year of peak song sparrow density. This study also described the impact of feeding on adult survival, discussed in ‘Provide supplementary food to increase adult survival’.