When I began studying bird nests I wanted to know how
birds could make something so complicated. Like many scientists, I now
realize I was asking the wrong question.
In fact, most bird nests are simple, made of just a few materials. A bird mostly uses only its beak to build a nest. Thatās like you trying to build a nest using only a finger and thumb on one hand. Nests need to be simple. But I discovered that even something that seems simple can be quite amazing when you take a closer look.
A bird Iāve been studying, called the long-tailed tit, uses more than 600 spider egg cocoons and probably 200 beak loads of moss to make its nest. To keep the chicks warm, there are about 1,600 feathers inside the nest. Thatās a lot of feathers! I figured a bird would have to fly a very long way to find so many feathers. I did an experiment to test this.
During nest-building season, I put out patches of feathers in the woods. Each week, I set out 20 patches, and each patch had 50 feathers. Each feather was marked with a two-color code. To color-code the feathers, I threaded a tiny piece of cotton through the shaft of the feather and sealed it with a small paint spot. The color of the thread told me which week the feather was used. The color of the paint told me from which patch it came. Altogether we color-coded 48,000 feathers!
After the baby birds were grown and gone, I collected
all the empty nests. Then I counted how many of our marked feathers were
in each nest. I was amazed by the findings: Of all the feathers in each
empty nest, only a very small number were marked feathers that came from
one of my patches. Remember that each nest has about 1,600 feathers. That
must mean thousands of feathers are available in the woods each week for
these birds to pick up. In fact, judging from where the birds picked up
my marked feathers, I estimate that these birds find all the feathers they
need for building within about 110 meters (about 120 yards) of their nests!
A red-billed weaver bird tying a knot about its perch.
The outside of the long-tailed tit nest surprised me as well. Dozens of white spider cocoons and more than 2,000 small pieces of lichen covered the nest. Lichen÷which often grow on trees--are made of both algae and fungus. People usually say that the lichen help hide the nest by making the nest look like lichen-covered branches. But my observations showed that these lichen-covered nests are not normally built on lichen-covered branches. Instead, they are built on plain, brown twigs that look nothing like the nest.
The lichen does make the nest look pale or ghostly. I can think of two ways of explaining this:
1. A pale-colored nest seems to fade into the light beyond
the branches, becoming almost invisible. Perhaps this makes it hard for
predators to find the nest.
2. Sunlight bounces off a light-colored nest and keeps the nest from heating up.
Now I need to do some investigations to find out which
explanation is true, or possibly both are wrong! One of the exciting things
about science is that you are always finding new things you want to understand.
Scanning Electron Micrograph of moss and spider silk.
Did you know birds "invented" Velcro before humans did? When I first started studying spider silk in nests, most people, including me, believed spider webs helped "stick" the nest together, kind of like Scotch tape. But as I looked at hundreds of nests, I noticed that birds do not use the sticky silk from webs but the fluffy, "loopy" silk from spider egg cocoons. When I looked under a microscope, I saw how the tiny leaves of moss slip into the silky loops of silk, binding the two together (see above). Just like Velcro! How wonderful. This natural Velcro makes it easier to build a nest and easier to change the shape and size of the nest as it fills up with growing, wiggling chicks.
Mike Hansell teaches in the department of zoology at the
University of Glasgow in Scotland, United Kingdom.
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