M. stellatarum drinks nectar from flowers. Experienced moths feed on
flowers of almost any size, colour and pattern. But Almut Kelber of the
University of TĂĽbingen wanted to know how a newly hatched moth finds its
first meal.

To find out, she presented day-old hawkmoths with artificial flowers made
from card or Plexiglas discs of different sizes, colours and patterns, and
counted the number of times the moths visited each one. From this she learnt
that size is the most important factor in determining a flower’s appeal, and
that 32 millimetres was the favoured diameter (Journal of Experimental
Biology, vol 200, p 827).

Ian Kitching, a hawkmoth expert at the Natural History Museum in London, says
that he has observed similar preferences among related moths living in Thailand.
“Kelber has found something real,” he says.

But why is size so important? Kelber, who is now at the Australian National
University in Canberra, believes it is to do with the way hawkmoths judge where
they are. Hummingbird hawkmoths use vision to find their way around, and judge
the distance to objects in front of them by noting how large they loom. If a
flower is too big, Kelber suggests, it may completely fill an approaching moth’s
field of vision, disorienting it and putting it at risk of flying into the
flower.

Kelber also found that the newly hatched hawkmoths preferred flowers giving
off blue light with a wavelength of 440 nanometres. Through the eyes of insects,
leaves and the ground are thought to look similar. Blue should contrast strongly
with this background, so a liking for blue provides an effective way of finding
flowers. As hawkmoths mature, they presumably become more skilled at recognising
flowers from the background, and so learn to feed on a wide range of flower
types.

Kelber notes that newly hatched honeybees show similar colour preferences.
She suspects that this may be an innate preference, hard-wired into most insects
by evolution. As they mature, however, insects will learn to choose flower types
specific to their ecological needs.

Birds reproduce through a “cloacal kiss” in which the male deposits sperm
from his cloaca at the opening of his partner’s. The female must then actively
draw the sperm up into storage tubules where they wait until she is ready to
release eggs. Only then are the eggs fertilised. Even then, a female can dump
the fertilised eggs if she does not want them.

Because the sperm are actively drawn in rather than passively received, the
female has complete control over whose sperm reaches her eggs. James Briskie at
the University of Oxford and Robert Montgomerie of Queen’s University in
Kingston, Ontario, compared species that have lost the penis—or, to be
more precise, the intromittent organ—and those that have retained it (
Journal of Avian Biology, vol 27, p 1).

In order to maximise her reproductive fitness, a female wants to choose the
best sperm. Although she can reject fertilised eggs, it is wasteful and costly.
Males that waste sperm by having it rejected will also fail, say Briskie and
Montgomerie, so the best strategy for them is to be actively chosen.

Females have most control over males without an organ. So, the researchers
reason, they would be chosen more frequently and would eventually have had
greater success than those who wasted their sperm.

Most of the birds that still have an intromittent organ are large, including
the ostrich and large aquatic birds such as geese. In these species the female
can afford to be less choosy: her eggs are small in relation to her body size
and therefore dumping her fertilised eggs is less costly.