Why are parasitic birds stronger than the host's offspring?

These particular birds belong to a group of parasitic (also known as egg-laying) species.

Parasitic bird parents use clever tricks to give their offspring a chance to thrive in the host family.

The brown-headed cowbird (Molothrus ater) lays eggs that look similar to the eggs of its various hosts for camouflage, while the mother birds take a more brutal approach of piercing many of the host's eggs, thereby eliminating their children's competitors.

Exercising in the eggs gives the parasitic birds an advantage over the host's offspring.

Although these mother birds have paved the way for the chicks, after hatching, the chicks will have to fend for themselves.

A new study published in the journal Proceedings of the Royal Society B: Biological Sciences shows that so-called embryonic movement - or exercise in the egg - can give competitive advantage to those parasitic bird relative to the host's offspring.

'Previous studies in domesticated birds, such as chickens, have demonstrated that embryonic movement is key to chick development,' said Stephanie McClelland, PhD, Royal Holloway, University of London in Egham. .

Some studies have shown that the more active the egg, the more muscular and muscular the chicks are born, while other studies show that in the opposite case, paralysis in the embryo causes stunted bone growth. .

So all birds benefit from 'exercise' from within the egg, as it helps them get ready for the outside world. 'Within a day or two after birth, they were able to lift an egg roughly their own weight on their back and push it out of the nest,' Stephanie McClelland said.

Stephanie McClelland and her team wondered how newly hatched birds had such magical powers. They hypothesized that the 'exercise' in the eggs had something to do with this. To test the hypothesis, the team analyzed 437 eggs from 14 bird species, including five foster parasites, their hosts, and several closely related non-parasitic species for comparison.

In general , parasitic birds have a very short incubation period . The brooding period of brown-headed cowbirds lasts only about 10 days, according to McClelland. This is supposed to be another survival strategy. With earlier hatching, the host has less time to detect and remove parasitic eggs.

In addition, pre-hatching also gives violent parasitic birds the opportunity to destroy eggs or kill young birds of the host. And the more gentle species, like the brown-headed cowbird, use their muscles to engage in 'intense feeding' behavior towards the adoptive parents, monopolizing the food supply provided before the host's eggs are available. bloom.

During their brief incubation period, parasitic species showed a higher percentage of motile embryos compared with host and non-parasitic species. Parasites' movements also increased at a higher rate during their incubation period than in other birds.