Tropical songbirds get their growth spurt late

Delayed development helps fledglings survive after leaving the nest

whitehead's broadbill and hermit thrush

MOUTHS TO FEED  Tropical birds like the Whitehead's broadbill (left) tend to raise fewer nestlings at a time than birds in temperate regions, like the hermit thrush (right). The reason may lie in how those babies grow, a new study suggests.

Both: T. Martin 

Scientists have long puzzled over why tropical songbirds lay fewer eggs than their temperate-zone counterparts.