& Learned Behavior
|In another section we see
that young pigeons don't need to learn how to fly, that their knowledge of flying is innate.
In this section some facts are stated that cause some to begin thinking that birds are
nothing but mindless little machines. To keep that idea from taking root, take a look at
the photo at the left. Cindy Mead in Michigan took that picture of a Cedar Waxwing during
a heavy snow and sent it to us. She said that the bird was catching snowflakes. I replied
that surely it was disgorging fruit "pits," or seeds, after having a big meal of
something like Hackberry fruits. I've seen them eat several such fruits, then fly to a
perch and as their stomachs removed the fruits' fleshy parts the birds would "cough
up" the hard pits. However, Cindy replied, "they were definitely catching snow
because some were 'pecking' at the air. No pits were spit."
So, as Cindy said, "Just when you think you've seen it all..." birds do something really unpredictable. I felt the same way when I first saw White-throated Sparrows taking "dew baths" -- flying into dew-wet leaves of mesquite trees in Mexico to wet their bodies as a form of bathing..
Anyway, let's think about innate behavior a little more. Here's another observation about White-crowned Sparrows:
Even when newly hatched White-crowned Sparrows are kept where they can't hear any kind of bird songs, when they're about a month old they begin singing simple notes. This bird babble, known technically as subsong, continues for about two months. When the birds are about 100 days old, their subsong "crystallizes" into a form that thereafter doesn't change much. The singing of White-crowned Sparrows of this age who have never heard other birds of their species sing is not nearly as rich and pleasant to hear as that produced by birds who have grown up hearing their own species' songs. Nonetheless, experienced birders can definitely hear the White-crowned Sparrow element in their song.
Think about it: The particular melody a bird sings is at least partly innate. Birds are actually born with the melodies of their species' song implanted in them!
If recordings of fully developed bird songs from a number of different bird species are played to young White-crowned Sparrows during their babbling stage, somehow the young sparrows pick out the song of their own species from all the rest -- even though they've never heard a well developed White-crowned Sparrow song before -- and begin imitating it.
Moreover, if the young birds are ever to sing their own species' song perfectly, it's absolutely necessary that they hear properly sung songs before they reach about seven weeks of age. In other words, there's a window of time when the song must be heard. This "window" is known as the sensitive period. If birds hear their song only before or after the sensitive period, they'll never produce fully developed, beautiful White-crowned Sparrow songs.
Innate behavior is hardly evident only in pigeons and White-crowned Sparrows. One of the most striking cases of innate behavior in birds has been documented by placing a "window" in an incubating chicken egg, and watching the unhatched chick as it develops. Unhatched chicks move their heads, open and close their beaks, and even make pecking movements. Clearly, nothing has taught the unhatched chicks to peck. They are simply created with the pecking urge, or instinct.
The same is true when a Canvasback duckling has just hatched, and immediately after drying off can walk, swim, and, if necessary, dive below the water's surface -- even if the duckling has been hatched in an incubator, and couldn't have possibly learned walking, swimming, and diving from any other creature.
Some innate behavior doesn't appear until the bird is an adult. When a female Canvasback duck is about a year old and builds her first nest, she builds a nest exactly like all other Canvasbacks, even if she has been kept in isolation, and couldn't have learned Canvasback nest-building technique from another duck.
An important point about the pecking chicks inside incubating, unhatched eggs is that they begin pecking movements at a predictable time in their development -- about seventeen days after the egg is laid. It's as if incubating chicks were computers loading a program, and at a particular point in the program the command goes out, "Begin pecking movements." The same kind of thing happens with humans. We learn languages incredibly fast at a certain young age, but it's much harder both before and after that age.
It's fun to think about this subject. For example, in you, what's learned, and what's innate... ?