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Symbiosis, a term from the Greek, is what the biologist uses for the
living together of two dissimilar organisms. In a broad sense it
includes such diverse relations as the lice living on man and rats in
his house, the union of an alga and a fungus to form a lichen, and the
cross-pollination of flowers by hummingbirds.
The story of the burrowing owls of our Western plains living in amity
with prairie dogs and rattlesnakes as one happy family comes to mind
as an example. But "foolish nonsense" is how the noted biographer of
North American birds, A. C. Bent, characterizes such stories. He then
goes on to quote evidence as to what actually happens, and one can see
how the story originated. The prairie dogs, which are really plump,
dumpy, ground squirrels and not dogs at all, dig their burrows close
to each other on the prairie in colonies which have come to be called
prairie-dog towns, or dog towns or simply "towns." Burrowing owls also
take up their residence in these towns, probably because they find
burrows ready made and do not have to dig their own as they are quite
able to do.
MODERATELY PREDATORY The owls may make an occasional meal of a young
prairie dog, and a prairie dog may perhaps dine occasionally on owl
eggs, but on the whole owls and dogs get along on terms of easy
familiarity. Sometimes when alarmed, both may scuttle into the same
burrow for safety, but each has its own burrow. With the rattlesnake
it is different. The rattlesnake may live in burrows in the dog town,
but when it is hungry it eats owl or dog as occasion offers. While
the picture of a happy family of owl, dog, and snake is a myth, the
symbiosis of owl and dog, at least in the same colony, is striking.
In Africa there is a tiny falcon only about eight inches long which is
called a pygmy falcon because of its small size. When Dr. Friedmann was
studying the social weavers in South Africa, birds which nest in large
colonies under a common roof they make in a savanna tree, he found
these falcons occupying nest chambers in thriving weaver colonies.
There was no friction between the weaverbirds and the falcons, and they
were sometimes seen to sit side by side. When Friedmann collected three
of these falcons he found bird remains in their stomachs but they were
not remains of the social weavers. Apparently the falcons were feeding
largely on small birds, but they did not molest the weaverbirds which
had made the nests the falcons were using.
PARROT-DUCK-OPOSSUM MÉNAGE We occasionally find a mallard nesting in a
tree, on an old crow or hawk nest, and there are ducks like the wood
duck and the golden-eye, which usually nest in holes in trees, but a
South American duck called the tree teal habitually nests in a parrot's
nest. The parrots, called monk parakeets, make their nests in compact
colonies in the branches of trees, so close together that they form
a single mass. The tree teal's usual manner of nesting is to lay its
eggs in one of the chambers in this apartment-house colony. At first
the eggs are laid on the rough twig floor of the nest, but as the eggs
increase in number a lining of down, plucked from the breast of the
bird, is added until it may even extend out the entrance of the nest.
Apparently parrot and duck both get along amicably in their pendant
treetop cradles. An opossum sometimes also finds these parrot nests
to its liking, though one wonders if it may not have a meal of young
parrot or duck in mind. But be that as it may, in different chambers
of a single communal nest of these parrots, parrots, a duck, and an
opossum have been found.
On islets off the New Zealand coast lives a rather large-sized lizard
called _Sphenodon_. It's rather well known by name, at least, for it
is one of those relics of a formerly more widespread group which are
called living fossils. It is also noted for its remarkable development
of a pineal eye, the remnant of an important sense organ in ancestral
forms, and formerly an organ some philosophers supposed to be the seat
of the soul. But here we are interested in the fact that petrels swarm
to these same islands to dig their burrows and lay their eggs in them,
and it is in these same burrows that _Sphenodon_ spends its daylight
hours. Apparently the insect-eating _Sphenodon_ and the oceanic-feeding
petrels share the burrows amicably, adding still another example of a
rather long list of dissimilar organisms whose lives are associated.