Speaking of Nature: Baby birds
Go outside and listen carefully and you will hear the begging of hungry baby birds from almost every quarter. Summer is upon us and we will soon be up to our eyeballs in baby birds. In my own yard, I have baby bluebirds, tree swallows and house wrens that are all about to fledge in the next few days. But what governs the reproductive lives of our local birds? Timing is obviously important and huge numbers of birds migrate to our area for the specific purpose of breeding, but how do they decide “how” to breed?
Well, it turns out that size and lifestyle play huge roles in the reproductive strategies of our local birds. There are basically two different approaches that birds employ in their efforts to reproduce: you can either be “precocial,” or you can be “altricial.” That clears up everything, right? No? Well, I didn’t really think so. You’d better grab a cup of coffee and get ready for Bird Breeding 101: How they do it!
The first group has what are called “precocial” young. These species typically nest on the ground and the babies need to be able to follow their parent(s) to food and safety almost immediately after hatching. When the babies hatch, they are fully covered with down, their eyes are open, they have strong legs, they can hear and they are ready to go within hours of hatching Examples of precocial species are wild turkeys, ruffed grouse, ring-necked pheasants, ducks, geese, woodcock, killdeer and the various species of rails that nest in our area.
Precocial birds tend to lay large clutches of eggs, which can present a bit of a problem right off the bat. Typically, an egg can sit in a nest without being incubated for about seven days, but that time can be extended by cold weather. The embryo inside the egg is alive, but in a state of suspended animation. As soon as incubation starts, however, it cannot be interrupted without killing the growing chick.
But sometimes females can lay well more than seven eggs in a clutch. A hooded merganser hen can lay up to 12 eggs and wood duck hens can routinely lay up to 15 eggs in a clutch. Both are well beyond the seven-day limit, so what’s going on? Well, this is where the advanced development of the chicks comes into play.
Young precocial birds can hear before they hatch and it turns out that they can also “talk” while still in the egg. Their hearing allows them to learn the sound of their mother’s voice before they hatch, but it also allows the babies to talk amongst themselves. Precocial birds almost always hatch from their eggs in unison, as if they have discussed it beforehand. This probably allows all of the chicks to be old enough to get around before the group hatches.
Once they hatch, they need a short time to dry off, get a look at mom and then head out into the world, never to return to the nest again. In some species, the babies imprint on the first moving object they see and they will follow it wherever they go. This makes sense, because as long as everything is going as planned, the parent should be the first thing a baby bird sees.
Research has shown, however, that young precocial birds do not know what their parents look like, or even should look like. In a famous experiment, Konrad Lorenz (a rock star in animal behavior) showed that it was possible to get a family of young geese to imprint on a human; namely himself. Other researchers imprinted young ducks and geese on cows, people and even an outboard motor on the stern of a small boat. In the natural world, however, newly-hatched ducklings and goslings follow their mothers.
The other strategy produces ‘’altricial’’ young and they represent the majority of bird species from kingfishers to robins. Altricial birds are completely undeveloped and totally helpless when they are born, almost like a human baby that is born prematurely. They are blind, deaf, almost completely naked and they have only the beginnings of legs and wings.
Young altricial birds grow very quickly, however, and they undergo some amazing changes. Their skin darkens when the feathers start to grow, their eyes develop and then open, their legs and wings get stronger and longer and they begin to hear things about half way through their 12- to 14-day infancy. That’s right, in just two weeks they are ready to leave the nest and in six weeks they are probably self sufficient.
This process may take longer for larger birds — such as the large hawks, eagles, owls, herons and egrets — but for anything like a blue jay or a scarlet tanager, five to six weeks is all they need. By the time a robin is two months old, it has no need for a parent. At only four months of age, a robin born in Franklin County can start to fly to Mexico. How many parents out their are secretly wishing that their own children would take a trip to Mexico?
The key to all of this is the female bird’s access to nutrition prior to laying her eggs. If a female has a reliable food source and can amass a great deal of energy in her own tissues, then the yolks in her eggs can be big. In precocial species, the yolk is generally large, accounting for 25 to 50 percent of the egg’s weight. A larger yolk will mean that the baby bird in question will be better fed when it is inside the egg and therefore more developed, which is exactly what precocial chicks need to be.
Migratory species, like robins and warblers, use so much energy during their long trip to the breeding grounds that they cannot invest as much energy in producing big yolks. In altricial species the yolk can account for as little as 15 percent of the weight of the egg, which, in turn, will produce much smaller chicks. Instead, altricial species depend upon the bountiful explosion of insect life to feed their chicks with.
Then of course, there are those species that have figured out how to exploit humans for their own gains. I have a feeder on my porch that is specifically designed to hold peanuts. Made of hardware cloth in the form of a hollow tube, this feeder can hold several cups of peanuts in the shell, which you would think would last a while, right?
Well, the “insect-eating” woodpeckers in my neighborhood have learned that I will keep filling this feeder as quickly as they empty it. It also appears that I cannot resist the sounds of hungry baby woodpeckers begging for food. So all of the young woodpeckers are getting to be little butterballs on this unusually rich diet, while I am going through peanuts like they’re going out of style … and I love it. The more baby woodpeckers, the better!
Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. To contact Bill, or to learn more about his writing, visit