A good disguise could mean the difference between narrowly escaping a predator or winding up as a meal. But for birds that nest on different sorts of microhabitats, achieving successful camouflage might be trickier. What works on one surface would make them stand out on another nearby. Blue-footed boobies (Sula nebouxii) may have figured out a nice solution: Cover the eggs with whatever’s on the ground. And according to new findings published in The American Naturalist, the strategy works.
Over the course of decades, a team led by Fernando Mayani-Parás from National Autonomous University of Mexico observed 3,668 single-egg clutches on Isla Isabel in Mexico. Soil from the ground sticks to the boobies’ pale eggs, which moms and dads can manipulate using the webs of their feet.
Using digital images, the researchers confirmed that the pale eggs did become gradually dirtier during the first 16 days of their 41-day incubation period. And week one was the most treacherous, Science News reported: 47% of the eggs were lost to predation in the first five days. But over time, the eggs started to blend in with the nest substrate, and the probability of egg loss declined progressively – and then remained low for the rest of the incubation period.
Then to see if booby parents were doing something else to ward off predators besides slowly dirtying their eggs, the team conducted an experiment using chicken eggs. After soiling the eggs, the researchers exposed them in artificial booby nests. Dirty chicken eggs were less likely to be picked up by Heermann’s gulls (Larus heermanni) than clean eggs. “By darkening egg color behaviorally, boobies can potentially exploit a greater range of nest substrates than might otherwise be possible because the extent of egg camouflage can be flexibly manipulated to suit the local nest environment,” the authors write.
Image in the text: rebvt/shutterstock
[H/T: Science News]
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