Black-headed Grosbeak are big, robin-sized birds that are a gorgeous combination of Black, yellow and orange. They are so striking that people often confuse them with Orioles. They also have a long and loud song, like a whistling Robin, that they will sing over and over. So, how is it that they can hide so well? You can hear the bird and know it is “just right there!” But, then you can look for ages, initially intrigued, then more and more annoyed as they continue to evade detection.
This relatively common phenomenon brings up a couple of interesting topics. Natural selection has caused these brightly colored birds to evolve adaptations to avoid detection by predators. Only the males that successfully avoid being eaten end up passing their genes on to the next generation. So, they tend to sit still while singing, making sighting them more difficult. Their songs also are difficult to localize. They often sound much closer and higher up then they actually are – they throw their voices.
This then brings up the question of how can evolution cause these birds to avoid detection on the one hand and yet be brightly colored and loud on the other. The simple answer is that natural selection is not the only mechanism of evolution. Survival doesn’t automatically cause your genes to make it into the next generation. You also have to reproduce. So, behaviors and characteristics that help females find you and recognize you as a particularly studly male (e.g. bright coloration and long, loud song) will be passed on in greater abundance to the next generation.
Just because they are brightly colored doesn’t mean they are easy to see.
Top of page photo by Randy Patrick
David Benson Ph.D.
White-tailed Ptarmigan researcher and National Park Service Ranger Naturalist in GNP since 1995. "The Bird Ranger"