Image source: Photo by Geoffrey B. Hoover
Champaign, Illinois. Bird brood parasites lay their eggs in the nests of other bird species, forcing the families to do the hard work of raising unattached youngsters. A team of scientists wanted to simulate the task of puncturing the egg – a tactic that only a minority of host birds would use to help catch and expel the alien eggs. Their study provides insight into some of the physical challenges facing this characteristic host birds.
The new findings appear in the Journal of Experimental Biology.
Take cowbirds, for example. Study co-author Mark Huber, professor of evolution, ecology and behavior at the University of the United States, said that their eggs do not resemble those of host birds, “however, most of their hosts do not reject parasite eggs.” Hug a snooping expert. “One explanation is that the cow’s egg shell is so thick and sturdy that a small host’s beak cannot penetrate it.”
To determine whether the difficulty of penetrating the brood parasite egg played a role in whether the host bird was trying to eject it, Daniel Clark, an undergraduate working in Huber’s lab, teamed up with another professor in the same department, Philip Anderson, an expert in the biomechanics of piercing, slicing and stabbing. Anderson has previously studied the properties that contribute to the cutting and crushing ability of teeth and the extraordinary power of snake tusks and aloe vera spines.
The team used chicken eggs in the experiments because collecting and destroying wild bird eggs would be an ethical problem and difficult to standardize. The researchers wanted to determine what influences the egg’s ability to withstand the hole.
“The factors that we looked at specifically in the paper were the presence of a nest, the sharpness of the bird’s beak and the speed with which it collided with the egg,” Clark said.
The team measured the energy required to penetrate the eggs in different conditions: with or without a nest supporting the egg, with a supernatural object approaching the eggs at high or low speeds, and with faint or sharp objects. The researchers used the sharp end of the nail to simulate a sharp beak, and the nail tip as a substitute for a dull beak. Experiments included either a fast-swinging nail attached to a pendulum or a material tester that slowly pushed the nail into the egg.
The researchers said they were surprised to find that the dull end of the nail did a better job of puncturing the egg than the sharp end, especially when hitting the egg at a higher speed.
“My lab has done a lot of research on the mechanics of puncture and cutting, but we’ve always been looking at soft materials like skin or muscles,” Anderson said. “Eggshell is fragile – more like ceramic than leather. If you are trying to break something brittle, like glass, it makes more sense to use a hammer than using a knife, so this result was not as surprising as it seemed at first.”
Experiments have also revealed that the nests absorb some of the nail striking energy, especially when the nail is moving at slower speeds.
“In the slow motion experiment, the nest was of great importance, but the sharpness or dullness of the nail was less important,” Clark said. “In the fast-moving experiment, the nest was less important, but the sharpness of the nail matters a lot.”
The team also discovered that the act of repeatedly hitting eggs weakens the sharp end of the steel nails.
“This indicates that biological surfaces are much stiffer and more durable than we think,” said Clark.
If clicking a strange egg quickly at the bottom of the nest damages its beak, the host bird may reduce its ability to prepare, weave its nest, or feed itself and its young. These findings, the researchers said, provide clues to factors that influence how – and whether – a host bird responds to the arrival of a strange egg in its nest.
“Our experiments are helping us understand the long-standing mystery of why most bovine hosts and their clear eggs did not develop to remove the parasitic egg from the nest,” Hopper said.
The National Science Foundation and Joseph B. Hooks Research from USA this research.
To reach Daniel Clark, send an email [email protected]
To reach Philip Anderson, send an email [email protected]
To contact Mark Hopper, send an email [email protected]
The paper, “The nest substrate and tool shape greatly influence the mechanics and power requirements of boring bird eggshell”, is available online and from the US News Bureau.