[Illustration]
To use a bunch of flowers or a spray of leaves in decorating a room
in a house is a refinement of civilization. As the flowers fade, or
the leaves wilt, they are replaced with fresh ones. Sometimes a winter
bouquet is used that will serve for months.
There are several birds that habitually deck their nests with green
vegetation, and when it is wilted, it is renewed with fresh. The reason
is not clear. It has been suggested it is to supply humidity and, by
evaporation, coolness; it has also been suggested that its use serves a
sanitary purpose. But whatever the reason in birds' eyes, it looks like
decoration to human eyes.
This habit is common with a number of different hawks: for example,
the red-tailed hawk is reported sometimes to have its nest, a bulky
flat, basin-shaped structure in the crotch of a tree, "profusely and
beautifully lined with fresh green sprigs of white pine, which are
frequently renewed during incubation and during the earlier stages in
the growth of the young." The golden eagle is said to add green grass,
or green leaves often attached to the twigs from time to time to the
lining of the nest, especially after the young are hatched; and the
broad-winged hawk is said to add green leaves to the lining of its
nest. In quite another group of birds the same thing also occurs. A
carrion crow's nest in England was visited periodically from March to
August. Strangely no eggs were laid during this whole period, but the
birds remained in attendance. When found, fresh sprigs of oak leaves
were interwoven around the rim of the nest. On subsequent visits the
oak leaves were found to have been replaced with fresh ones, and the
leaves were kept fresh until late August.
The purple martin supplies another example. The nest boxes we put up
for them supply their main breeding places in some areas. "The parents
have a habit of collecting many green leaves and placing them in the
nest, a practice which may tend by evaporation to reduce the heat" in
the next box. "Where large colonies are breeding they sometimes injure
pear trees by stripping certain branches of their leaves," according to
E. H. Forbush.
A Madagascar weaverbird provides an example of decorating the nest
entrance of a quite different type of nest; in this case the nest is in
the shape of an inverted retort, with the entrance through the spout.
The entrance is decorated with green grass heads or with green leaves,
and the males keep adding fresh green decorations even when the eggs
are being incubated by the female.
It seems hard to believe that this is really decoration, that it is not
for some purpose--either connected with the raising of the young, or
more probably a leisure or substitute activity--something to keep the
bird busy and strengthen the bond between bird and nest when it is not
otherwise directly occupied with nesting activities.