Brood Parasites Birds Exercise While Inside Their Eggs Before Hatching To Kill Nestmates

According to a new study, newly hatched birds exercise while in their eggs before hatching to develop the strength they need to mutilate and eventually kill their nestmates.

A Live Science report specified that these tiny creatures might appear "delicate and feeble," but some chicks are bursting out of their eggshells, all set for brawling.

Essentially, the birds are part of a group of species identified as "brood parasites" whose mothers are laying their eggs in other nests of birds, leaving them for other bird parents to breed.

Instead of exerting time and energy to raise their own offspring, brood parasite parents are using both clever tricks and physical strength to provide their babies with a combatting chance with their so-called foster family.

For instance, the Molothrus later, a brown-headed cowbird lays an egg that's similar to those of its various hosts, while the Indicator species called greater honeyguide moms are taking the more aggressive style of puncturing many of the eggs of their hosts, therefore, killing the chicks of the hosts and leaving their brood with less competition.

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Egg Exercise

Even though these bird mothers are setting their offspring up for success, the chicks are taking matters into their own wings once they're hatched.

Now, the new research published in the Proceedings of the Royal Society B: Biological Sciences journal has proposed that the "so-called embryonic movement" also called "egg exercise," may provide the chicks with a competitive advantage over their foster siblings.

According to a doctoral candidate and the study's first author Stephanie McClelland, from the Royal Holloway, the University of London in Egham, previous research in domestic birds such as chickens, among others, has shown that embryonic movements are key to the development of growing chicks.

Researchers have also suggested that hyperactivity in the egg leads to a beefy muscular chick, while other studies like the one published in the Journal of Morphology, have presented that paralysis in an embryo leads to stunted bone growth, deformed joints, and reduced muscle tone.

Therefore, all birds benefit from embryonic movement as it readies them for the world outside their eggshells. However, the early lives of avid offspring parasites are inclined to be distinctly strenuous.

Honeyguides

McClelland explained, birds have quite a difficult task when they hatch in a nest filled with big, lumpy barbet nestmates that they need to bite using their hook.

This may explain the reason fewer honeyguides, as described in the Beauty of Birds site, are doing more egg exercise before hatching compared to the greater honeyguides, which don't have trouble shaking their weak nestmates to death.

The embryonic movement or egg exercise of greater honeyguides is very akin to that of their hosts, suggesting that birds don't require much muscular training to take out the tiny eaters of bees.

Looking ahead, McClelland continued explaining she's planning to investigate what factors are actually triggering embryonic movement in the different bird species.

Hormonal and Genetic Factors Suspected as Main Drivers

Environmental factors like temperature may have played a vital role in when and how vigorously the developing chicks are moving. Since the parasites and hosts share nest, McClelland suspects that hormonal and genetic factors may be the main drivers behind egg exercise.

The team is looking into the energy use of birds, as well, during this critical period of development, provided that they are limited to using their yolk within their eggs.

The first author explained that it is quite mysterious what's going on inside the eggs. This new research is undoubtedly a starting step. McClelland added that a lot more work will be needed to link how such a movement shapes these birds.

Related information about bird behavior is shown on Cambridge University's YouTube video below: