I saw the most adorable thing the other day while working in the yard. Inside the nest above our garage light were four baby robins, blindly bobbing up and down in eager anticipation of a meal. After a few moments, a robin landed in the nest and began feeding the brood. Once the worm had been devoured, the robin flew away for more grub, and still the babies bounced up and down. It amused me so much – the birdie siblings with their open beaks just barely visible above the well built nest.
I’ve kept my eye on the nest since, and I’ve discovered that the mom and dad work in pairs pretty equally to feed their tots. That can only mean one thing; the eggs must have been a bright, bright shade of blue. More passionate about spying on robins than I am, Professor Bob Montgomerie at Queen’s University recently published findings that male robins contribute more to the nest-hold when the eggs are a vivid shade.
Eggs get their coloring from pigments they absorb while inside the female bird. The beautiful color of robin’s eggs comes from a pigment called biliverdin. Healthier eggs seem to have higher amounts of biliverdin, and thus a richer color. In his experiment, Montgomerie replaced real eggs with fake eggs of varying hues. When the incubation period for the real eggs drew near, Montgomerie placed newly hatched robins in the nests. The babies from the brighter “eggs” received twice as much food from fathers as the ones from the less brilliant “eggs.”
And here I thought that only mom robins attended their nest’s nursery.
I read up a little more on eggs in an artsy book by Maryjo Koch called Bird Egg Feather Nest. Amongst her beautiful artwork she included some interesting trivia about eggs. She explained that the blue of the robin’s egg keeps out dangerous sun rays, kind of like built-in sunglasses. Another fun tidbit, birds know intuitively how many eggs to lay based on how many they can feel under them. In one somewhat cruel experiment, scientists removed a laid egg from a northern flicker’s nest every day, prompting the poor bird to lay 71 eggs in a period of 73 days!
After much pondering, I have to agree with Koch who writes, “Propagation is work. Real work. How a bird manages to charm a mate, design and construct a nest, incubate eggs, feed hatchlings incessantly, and defend its territory, seems an exhaustive, if not impossible, feat!”
I’m glad the baby robins above the garage hatched from bright blue eggs, though. The task of raising the nest-full of greedy, bobbing youngsters seems to be a slightly easier one with both parents hunting for worms!