Why tropical songbirds have fewer chicks?

Life history trade-offs: why tropical songbirds have fewer chicks

Tropical songbirds produce fewer, high-quality nestlings per breeding effort than do songbirds that breed in temperate zones, according to a study published today. This study reports that tropical songbirds’ nestlings grow longer wings, and faster, which means they spend less time in the nest where they are vulnerable to predators

red-faced warbler Thomas Martin/Science 2015
An adult red-faced warbler, Cardellina rubrifrons, feeds its hungry nestlings. The red-faced warbler is a small bird that lives in montane forests of mixed conifer and oak at elevations from 2,000 to 3,000 metres (6,600 to 9,800 ft) above sea level. It is migratory; breeding in New Mexico and Arizona, and wintering in El Salvador, Guatemala and Honduras. Photograph: Thomas Martin/Science 2015