In the cities, male sparrows do it all

Male song sparrows take their father position very seriously when they’re living in the city—they defend their nests and take care of their chicks at the same time.

That was surprising to researchers, who thought they might have to spend more time aggressively maintaining their territories and would have to trade off parental care with females.

“Urban sparrows are more bold and aggressive than their rural counterparts,” said Samuel Lane, a National Science Foundation postdoctoral research fellow in biology at North Dakota State University. “But we didn’t really understand the consequences of this increased aggression.”

Lane led a study in Kendra Sewall’s lab at Virginia Tech that was published in Frontiers in Ecology and Evolution testing out how aggressive and paternal male urban and rural song sparrows (Melospiza melodia) were and comparing how successful they were at raising young.

To conduct the research, Lane and his team first had to catch some birds. They caught them in mist nets and fitted them with PIT tags—coils of magnetic wire encoded with a unique ID. Whenever the tag got close to an antenna at the nest, it would record the unique ID.

At the beginning of the breeding season, Lane and his colleagues played sounds of another male in the center of song sparrow territories in both urban and rural areas in southwestern Virginia. They also placed 3D-printed song sparrow mounts to represent another bird. They recorded how close each bird got to the mount and how many wing waves and vocal displays the males performed over 6 minutes, as a way to determine how aggressively they were defending their territories. The researchers also recorded parental care and nest success.

They found that for urban birds, there wasn’t a tradeoff between parenting and aggression. “Essentially, if you’re going to look for the most aggressive and the most paternal dads, they were all in urban habitats, which was super surprising,” Lane said.

Lane said this is likely because the urban males are freed from some of the constraints that exist in rural habitats, especially predation.

Nesting success was also higher in urban locations. In some years, 80% of the nests were predated in rural areas, but predators were probably fewer in urban areas, and urban predators like raccoons (Procyon lotor) and opossums (Didelphis marsupialis) are more likely to eat trash than birds.

The findings suggest that song sparrows do better in urban areas. “Song sparrows are very hardy, and they seem to readily acclimate to these urban environments,” he said. They may also benefit from consistent food and water in urban habitats from things like agriculture and from other resources like shrubs.

Lane hopes this research adds to the body of knowledge of how different species perform in urban environments. “In general, you see decreases in biodiversity as you move into urban habitats,” he said. “But there’s some species that do really well in urban habitats. What we hope is that by continuing to do research like this in urban ecology, you can better understand what these animals are benefiting from in urban environments and hopefully design these urban environments to better support wildlife.”