Tropical Songbirds Care More for Their Young Than Temperate Cousins

It turns out that where a songbird lives may impact its reproduction and, ultimately, its survival as a species. Scientists have found how parents care for the young and how well young survive is based on where the songbirds live.

"A bird species' risk of death among life stages, together with growth strategies of young, is a pivotal basis for a major leap forward in understanding latitudinal variation in life history strategies of songbirds," said Thomas Martin, one of the researchers, in a news release.

In this latest study, the scientists studied growth and nest predation of 20 to 30 co-existing songbird species in Venezuela from 2002 to 2008 and Malaysia from 2009 to 2014. The researchers also studied songbird nests in Arizona the past 28 years.

The researchers found that tropical songbirds typically only raised two young while temperate species raised four or more. However, the tropical offspring were more likely to survive.

Offspring of tropical species were thought to grow slower than those living in the Northern Hemisphere. That slower growth suggests that they spend more time in the nest and are at greater risk of being killed by predators. Since tropical songbirds' nest predation risks are equal to, if not higher than, temperature birds, researchers expected them to grow as fast as temperature birds rather than slower.

However, that's not what researchers found. Instead, the tropical birds rely on the greater parent-to-offspring ratio so that the tropical nestlings wind up with more nutrition to aid growth. Even so, they don't grow faster than their northern cousins.

"Provisioning, parental investment and mortality are all related," said Martin. "A later, faster growth spurt of tropical songbirds, together with higher parental effort invested per offspring, aids wing growth and flight capabilities after the young birds leave the nest. That previously unrecognized faster growth of wings among tropical species aids in escape from predators after young leave the nest."

The findings reveal that when it comes to survival, parental care is key for tropical birds. This is important to note when it comes to understanding how these species evolved.

The findings are published in the journal Science.

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