Nature bird study reveals how parents choose who goes hungry

Humans have long known that the early bird gets the worm, but new research just gave us a fresh aphorism: it turns out the scrawny chick often goes hungry. 

Speaking on CBC's Mainstreet, "Turf Guy" Andrew Hebda said a new study looked at how mother birds split their worms among their young. 

"If all things are equal and food is available, there's no issue," said Hebda, a biologist at the Museum of Natural History in Halifax. 

Raising a brood successfully puts a metabolic demand on breeding birds that is the equivalent to a human cycling the Tour de France.- Nature study

"But if food becomes scarce, they [mother birds] look for other signals. In other words, they look and see who has the better chance of surviving in these conditions."

The study, recently published in Nature, found that mother birds may choose to neglect begging chicks in favour of larger, healthier chicks.

"Surprisingly ... in a quarter of species studied, parents ignore begging chicks. Furthermore, parents in some species even neglect smaller chicks that beg more and preferentially feed the biggest chicks that beg less," the study authors write. 

It's brutally pragmatic: by sacrificing the weak so that the strongest are fed, the mother bird increases its chance of passing along its genes.

Mother birds decide whom to feed based on health-indicating factors such as size and beak colouration.

Nova Scotian birds spared brutal calculation

The study included data from 306 studies that looked at over 140 species of birds. A few common species from Nova Scotia were included in the study, including swallows and starlings.

Hebda says Nova Scotia's climate means mother birds rarely have to make such difficult choices. 

"The supply of food here is quite consistent, so most of the species that we have will produce large broods," Hebda says. 

So rest easy this spring, knowing that those chirping chicks are probably going to be fed soon. The study found that in good times, parents feed the scrawny, hungry chicks first. 

"In many species, including our own, the production of offspring represents the most energetically demanding stage of an animal's life," the study says.

"Raising a brood successfully puts a metabolic demand on breeding birds that is the equivalent to a human cycling the Tour de France. Success or failure often depends on parents' ability to determine which offspring to invest in, when to invest in them and how much to invest."