Some birds even look after younglings that aren’t theirs. Others abandon even their own. Robins reject natural impostor eggs less than they do plastic impostors.
For their study, published earlier this week, on Tuesday, May 26, 2015, in the PeeJ Journal, researchers at the Hunter College of the City University of New York used 3D printing technology to print a number of eggs that sometimes naturally get dropped by brood parasites into the nests of other birds.
Brood parasites are birds that don’t take care of their own hatchlings. They don’t even build nests. Instead, they move their eggs into the nests of other bird species that are qualified to look after them and leave it to these host birds to raise the baby birds believing that they’re their own. It is an unfortunate habit that has often affected how the host bird raises her own hatchlings.
Their goal of the researchers was to study the behavior that American robins and their brood parasites, the brown-headed cowbirds, typically exhibit when encountering an alien egg in their nest. They were wondering about how important the shape, color, pattern and size of an impostor egg is to its own survival in the robin’s nest in particular.
It is important to note that the two (2) species have very different looking eggs. Robins have blue eggs, while brown-headed cowbirds have beige eggs, though natural cowbird eggs often manage to fool robins.
Egg-rejection studies and experiments have been done before. Scientists usually use materials such as wood or plaster to create the fake eggs. But now, the Hunter College scientists have used a new alternative – plastic printed 3D models. This allowed the scientist to leave these eggs hollow and fill them with gel in order to give them a more realistic feel.
They then painted them blue and green in order to make them resemble real American robin eggs, or painted them using beige in order to make them resemble real brown-headed cowbirds eggs.
They sneaked the eggs in various robin nests and surveyed the parent birds for the next six (6) days.
The results were similar those of previous studies, there was no significant change in egg rejection rates. When finding a fake egg made to look like one of their own, the robins accepted it 100 percent (100%) of the time.
When finding a fake egg made to look like a brown-headed cowbirds egg, the robins only accepted it 21 percent (21%) of the time. That’s a rejection rate of 79 percent (79%).
Don Dearborn, chair of the biology department and brood parasitism expert at Bates College, is an expert who was not involved in the study.
He gave a statement in a press release saying that “Hosts of brood parasites vary widely in how they respond to parasitic eggs, and this raises lots of cool questions about egg mimicry, the visual system of birds, the ability to count, cognitive rules about similarity, and the biomechanics of picking things up”.
He went on to add that for decades, if researchers wanted to tackle these questions, they had to make their own fake eggs, which is something that they all find to be slow, inexact and frustrating. Since this study uses 3D printing for a more nuanced and repeatable egg-making process, the technology in turn will allow more refined experiments on host-parasite co-evolution.
Image Source: deviantart.net