Lovell et al., Current Biology
Eggs come in a multitude of colors and patterns, from subtle pastels to vivid bright hues. Now a new study, published in Current Biology, supports a centuries-old theory that shell variation, at least for some birds, helps to camouflage eggs.
The masters of egg disguise turn out to be Japanese quail. This photo amazingly features eggs just from this one species. Mother quails somehow learn the patterning of their own eggs and choose laying spots to hide them best.
“We currently do not know the mechanisms by which the (mother) bird learns its own egg patterns,” lead author P. George Lovell of Abertay University and the University of St. Andrews, told Discovery News.
Nevertheless, the ground-nesting birds often perfectly match the eggs to substrate, helping to prevent the precious contents from being some hungry predator’s dinner.
Lovell et al., Current Biology
Close-ups of the individual Japanese quail eggs really show how well the bird moms can match their eggs to the environment.
One of the first scientists to theorize that coloration and speckles evolved for camouflage against predators was Alfred Russel Wallace, who gained fame as Charles Darwin’s co-discoverer of the principle of natural selection.
Lovell et al., Current Biology
Yet another Japanese quail egg matches its environment, but the egg is not invisible to us. “Some have asked why they can still see the eggs if they are camouflaged,” Lovell said. “It’s important to remember that the eggs are less visible, not invisible…The photographs are taken quite close up to the egg, and a predator wouldn’t necessarily be that close. It would be scanning an area, rather than staring straight at the egg.”
Japanese quail themselves are brown and speckled, like their eggs. The bodies of many birds appear to match their eggs. A parent bird could then likely better shield the egg when resting upon it.
Speckles appear to be key to camouflage, at least for eggs.
Avian expert Innes Cuthill of the University of Bristol’s School of Biological Sciences, told Discovery News, “Alfred Russel Wallace concluded that the brown and speckled colors of many eggs had evolved as camouflage against nest predators and that the ancestral color of white only persisted in species whose eggs were laid in well-protected cavities, were covered by nest material or, in birds such as ostriches, could be defended by their parents.”
Brown with speckles is just one egg color/pattern combo, as these reed warbler eggs reveal. Their greenish hue, set off by the green leaves surrounding the nest, would make them less visible to predators scanning the area from a distance.
This nest also includes a, slightly larger, common cuckoo egg. Demonstrating another bit of bird trickery, common cuckoo mothers frequently match the appearance of their eggs to those of reed warblers, which wind up caring for the hatchlings.
Sometimes avian parents enjoy the best of both worlds: camouflage for their eggs as well as fooling other birds. Cuckoo finches can be deadbeat parents, matching their eggs (seen in the inner circle) to those of the tawny-flanked prinia (outer circle). The prinia parents are sometimes fooled into caring for the cuckoo finch eggs and later hatchlings.
A mother cowbird must have worked hard to find this perfect spot for her eggs. “Interestingly, all birds seem more concerned in minimizing the mismatch between nest and the darker speckles on their eggs than the mismatch between nest and the underlying, predominant egg color, but particularly so for birds with more dark speckling,” Cuthill said.
Lovell and his team speculate that the dark and light markings serve as a disruptive camouflage, breaking up the outline of the otherwise revealing oval shape. That shape, for humans and countless other predators, serves as a visual signal for good eats.
This cockatiel, with its proud expression, has a right to boast. Its egg not only matches the mother bird’s coloration, but it also matches the environment. In the wild, a hunter would have a hard time finding such an egg.
By itself, the egg of a swan is just as visible as a bright white egg on a breakfast plate. Under the mother swan, however, the egg disappears.
Robert Ricker, NOAA/NOS/ORR
This Adelie penguin laid a speckled egg that matches its environment. The matching phenomenon could lead to a twist to the old riddle: Which came first, the chicken or the egg? In this case, the teaser could be: Which came first, the egg color and pattern, or the choice of nesting site?
An even more compelling mystery concerns a common sight in springtime—bright blue eggs in a robin’s nest. To human eyes, they are beautifully unmistakable. They stand out from both the nest and the parent birds, so why are they bright blue?
No one yet knows for sure. Biologists do know that pigment glands in the mother bird’s body deposit the blue coloration onto the eggs, so it must have a critical function. Perhaps the dark color camouflages the eggs when the eggs are at the bottom of a dark nest, or the blue might blend in with the sky for some viewers. Some researchers have even speculated that the striking color helps mother birds to find their own eggs.
For now, however, the case of the mysteriously blue robin’s egg has yet to be cracked.
Wild finches in the Galapagos Islands "self-fumigate" by using a human-made pesticide to kill parasitic fly maggots, a study in the latest issue of Current Biology reports.
Birds, like the rest of us, like to be the boss. Instead of treating maggot-infested nests directly, biologists are setting out pesticide-treated cotton balls, which finches are grabbing as material for building nests.
It's helping to rid nests of maggots, which may feed on the blood of baby birds, sometimes leading to their deaths.
The pesticide, permethrin, is safe for the birds, according to senior author Dale Clayton, a University of Utah biology professor.
"It might kill a few other insects in the nest," Clayton said in a press release. "This is the same stuff in head-lice shampoo you put on your kid. Permethrin is safe. No toxicologist is going to argue with that. The more interesting question is whether the flies will evolve resistance, as human head lice have done."
A colleague of Clayton's, Sarah Knutie, came up with the clever idea while studying animals in the Galapagos Islands. The finches here are related to Charles Darwin’s famous finches, which helped the renowned British naturalist to formulate the theory of evolution after he observed incredible diversity among the birds.
Knutie noticed that the finches "were coming to my laundry line, grabbing frayed fibers from the line and taking it away, presumably back to their nests." (The industrious birds were also collecting toilet paper, as well as string and fibers from towels.)
Knutie and her team built wire-mesh dispensers, filling them with cotton balls treated with 1 percent permethrin solution. At least four species of Darwin’s finches grabbed the balls and incorporated them into their nests.
All of the nests with the treated balls showed a significant reduction of the parasitic maggots. Effectiveness depended upon the number of cotton balls. Just a thimbleful of treated cotton can kill 100 percent of the destructive fly larvae.
"We are trying to help birds help themselves," Clayton explained. "Self-fumigation is important because there currently are no other methods to control this parasite."
The researchers think that other species might benefit from self-fumigation too. They mention that Hawaiian honeycreepers are suffering now from feather lice, while flies terrorize birds in Puerto Rico. The endangered Florida scrub jay is fighting back fleas.
Self-fumigation isn't just for the birds either. In the future, the same method might be used on the black-tailed prairie dog, whose populations have been declining in the Great Plains due to fleas infected with plague bacteria.
Photo: A finch in Ecuador's Galapagos Islands pulls a cotton ball from a dispenser set out by scientists. Credit: Sarah Knutie, University of Utah.