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
Thursday 27 August 2015 19.00 BSTLast modified on Monday 31 August 201513.32 BST
It has been a long-standing ornithological mystery as to why tropical songbirds have smaller clutches of eggs and raise fewer chicks per breeding effort than do temperate songbirds. But today, a study published in the journal Science argues that life history strategies lie at the heart of this conundrum. In this study, evolutionary ecologist Thomas Martin, an Assistant Unit Leader and Senior Scientist at the Montana Cooperative Wildlife Research Unit at the University of Montana, compares nestling growth rates between closely-related species of tropical and temperate songbirds. He documents that nestlings of tropical songbirds grow longer wings, and grow them faster, than do nestlings of temperate songbirds. Further, they achieve longer wings without increasing their time in the nest, which reduces their risk of predation. Further, because tropical songbirds have more resources available to invest into their offspring, they produce fewer chicks per breeding effort and invest more resources into each individual, thereby giving their offspring a higher survival rate after they fledge (leave the nest). In contrast, temperate songbirds have fewer resources available to nurture their chicks and their offspring suffer a higher mortality rate after they leave the nest, so temperate songbirds compensate by producing a greater number of lower-quality offspring.