This news release is available in Japanese.
Why tropical songbirds have fewer offspring than temperate songbirds, a long-standing puzzle, may lie in their distinct life history strategies, including the increased attention tropical songbirds show to their young. To identify an explanation for the small clutch size phenomenon in tropical songbirds, Thomas Martin analyzed the growth rates of tropical and temperate nestlings in the U.S., Malaysia and Venezuela. Tropical birds achieved longer wing growth sooner, meaning they spent less time in the nest, vulnerable to predation. Martin suggests that similarly rapid, advantageous, and resource-intensive wing growth is not seen in temperate species due to fewer resources available to them to nurture high-quality young. Temperate species focus on having more, lower-quality offspring because their offspring tend to die as young adults at higher rates, Martin says. By contrast, tropical songbirds, which have fewer offspring but are able to invest more resources into them, provide their young with a better chance of adult survival (as reflected in the rapidly developed, longer wings).
Article #12: "Age-related mortality explains life history strategies of tropical and temperate songbirds," by T.E. Martin at U.S. Geological Survey in Missoula, MT; T.E. Martin at University of Montana in Missoula, MT.