Feeders and crows bad news for robins
Bird feeders that attract crows could spell bad news for the red breasted robin, a new study found.
In areas of lots of feeders and crows less than one-per-cent of robin nests survive the 28 days to fledging.
But in areas with fewer feeders and crows, up to 34 per cent of robin nests survive.
Tables and feeders attract not only favourite garden visitors but predators that eat eggs and nestlings.
But birds of prey may also feed on the abundance of seeds and nuts so are less likely to target nests.
A four-year-long study looked at whether putting up artificial feed stations was harmful to songbirds in urban Ohio.
Researchers at The Ohio State University said while robins suffered on balance putting out feeders was a good thing for other bird species.
The study tracked the "complex" relationships between the success of American Robin and Northern Cardinal nests, the presence of potential nest predators like squirrels, domestic cats, and other birds, and the presence of bird feeders in the area.
Associate wildlife biologist Dr Jennifer Malpass said: "We found evidence that supplementary food has the potential to increase the relative abundance of certain predators, but not necessarily in a way that raises the risk of nest predation.
"Although the relative abundance of two nest predators, crows and cowbirds, was greater in areas with bird feeders, there was no consistent relationship between the number of bird feeders and predation of either robin or cardinal nests.
"Rather, we found that the number of bird feeders interacted with the relative abundance of nest predators, such that nest survival rates decreased only for robins in neighbourhoods with many feeders and many crows.
"Thus, our results show that supplementary food does not necessarily increase the risk of predation for breeding birds, and instead likely has nuanced and species-specific consequences."
She added results suggested: "The nest survival of robins declined with higher numbers of bird feeders only where the relative abundance of crows was highest, which suggests that crows may have been attracted to areas with high numbers of bird feeders, but that birdseed did not replace robin nest contents as a food source."
But she concluded: "Bird feeding is an immensely popular activity and, although its ecological effects are only beginning to be explored, the social effects of bird feeding are usually positive.
"Residential neighbourhoods provide a key venue for reconnecting city dwellers to wildlife, and urban birds are generally perceived favourably and provide a likeable link to nature.
"Bird feeders allow residents to more closely engage with wildlife and may help to foster environmental awareness.
"In addition, the development of best management practices can help to limit any potential negative ecological effects of bird feeders on birds, such as disease transmission and risk of window strikes
"Although results from our research suggest that providing supplementary food may not enhance nest survival for two species that frequently breed in residential yards in our system, the cultural benefits of bird feeding may outweigh the potential negative effects of bird feeders for common backyard birds."
The study was published in The Condor: Ornithological Applications.